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The ASTIS database cites the following 94 publication(s) by Garry Clarke. Publications are listed from newest to oldest. Please tell us about publications that are not yet cited in ASTIS.


Spring and summer monthly MODIS LST is inherently biased compared to air temperature in snow covered sub-Arctic mountains   /   Williamson, S.N.   Hik, D.S.   Gamon, J.A.   Jarosch, A.H.   Anslow, F.S.   Clarke, G.K.C.   Rupp, T.S.
(Remote sensing of environment, v.189, Feb. 2017, p. 14-24, ill., maps)
References.
ASTIS record 83075.
Languages: English
Web: doi:10.1016/j.rse.2016.11.009
Libraries: ACU

Satellite-derived land surface temperature (skin temperature) provides invaluable information for data-sparse high elevation and Arctic regions. However, the relationship between satellite-derived clear-sky skin temperature and various downscaled air temperature products for snow covered sub-Arctic alpine regions remain poorly understood, such that trend analysis or air temperature product integration is difficult. We compared monthly average air temperatures from two independent downscaled temperature products to MODIS Land Surface Temperature (LST) and air temperature at nine meteorological stations situated above tree-line in the southwest Yukon, Canada, between May and August 2008 for a full range of snow cover fractions. We found that both downscaled products generally agreed with LST for the low elevation, snow-free, vegetation classes. However, a systematic cold bias in Average LST emerged for snow fractions greater than approximately 40%, and this bias increased in magnitude as snow cover increased. In these situations the downscaled air temperatures were 5-7 °C warmer than Average LST for snow fractions of > 90%, and this pattern was largely independent of the number of measurements of LST within a month. Maximum LST was similar to average air temperatures for high snow fractions, but Minimum LST was colder by 10 °C or more for all snow fractions. Consequently, the average of Maximum and Minimum LST produces the cold bias, compared to air temperature, for high snow cover fractions. Air temperature measured at nine meteorological monitoring stations located between elevations of 1408-2690 m, on land cover classes Barren, Sparsely Vegetated or Permanent Snow and Ice, confirmed the cold bias results when incorporating Minimum LST in monthly averages. For snow fractions of < 40% the RMSE for all of the temperature products was < 2.5 °C when compared to station air temperature and all biases were positive and < 2.0 °C. For snow fractions of > 40%, the average LST bias became strongly negative at 4.5 °C, and the RMSE increased to 6.1 °C, whereas the downscaled products bias and RMSE were similar to those from snow fractions of < 40%. A weak warm bias for all the temperature products occurred for small snow fractions over non-forested land cover classes. Downscaled air temperature fields show physically real differences from Average LST in spring and summer, caused by snow cover and the interplay of Maximum and Minimum LST. These findings indicate that the integration of MODIS LST with downscaled air temperature products or local air temperature requires the incorporation of snow cover. (Au)

E, A, H, F, J
Alpine tundra ecology; Atmospheric temperature; Climate change; Clouds; Diurnal variations; Glaciers; Infrared remote sensing; Mountains; Plant cover; Satellites; Seasonal variations; Snow cover; Spatial distribution; Surface properties; Surface temperature; Weather stations

G0811
Burwash Landing, Yukon; Haines Junction, Yukon; Kluane Lake region, Yukon; Logan, Mount, Yukon; Yukon


A short and somewhat personal history of Yukon glacier studies in the twentieth century   /   Clarke, G.K.C.
(The Kluane Lake Research Station : 50 years of northern science. Arctic, v. 67, suppl. 1, 2014, p. 1-21, ill., map)
Open access available on the Web.
References.
ASTIS record 79575.
Languages: English
Web: http://pubs.aina.ucalgary.ca/arctic/Arctic67-S-1.pdf
Web: doi:10.14430/arctic4355
Libraries: ACU

Glaciological exploration of the Yukon for scientific purposes began in 1935, with the National Geographic Society’s Yukon Expedition led by Bradford Washburn and the Wood Yukon Expedition led by Walter Wood. However, Project “Snow Cornice,” launched by Wood in 1948, was the first expedition to have glacier science as its principal focus. Wood’s conception of the “Icefield Ranges Research Project” led the Arctic Institute of North America (AINA) to establish the Kluane Lake Research Station on the south shore of Kluane Lake in 1961. Virtually all subsequent field studies of Yukon glaciers were launched from this base. This short history attempts to document the trajectory of Yukon glacier studies from their beginnings in 1935 to the end of the 20th century. It describes glaciological programs conducted from AINA camps at the divide between Hubbard Glacier and the north arm of Kaskawulsh Glacier and at the confluence of the north and central arms of Kaskawulsh Glacier, as well as the galvanizing influence of the 1965 - 67 Steele Glacier surge and the inception and completion of the long-term Trapridge Glacier study. Excluded or minimized in this account are scientific studies that were conducted on or near glaciers, but did not have glaciers or glacier processes as their primary focus. (Au)

F
Aerial surveys; Arctic Institute of North America. Icefield Ranges Research Project; Drainage; Drilling; Equipment and supplies; Expeditions; Firn; Flow; Glacier lakes; Glacier surges; Glaciers; Glaciology; Instruments; Kluane Lake Research Station; Laser remote sensing; Mathematical models; Measurement; Radar; Research; Research stations; Temperature; Temporal variations; Wood, Walter Abbott, 1907-1993

G0811
Donjek Glacier, Yukon; Hazard Glacier, Yukon; Hubbard Glacier, Alaska/Yukon; Kaskawulsh Glacier, Yukon; Kluane Lake region, Yukon; Logan, Mount, Yukon; Rusty Glacier, Yukon; Seward Glacier, Alaska/Yukon; St. Elias Mountains, Alaska/British Columbia/Yukon; Steele Glacier, Yukon; Trapridge Glacier, Yukon


New insights into Late Pleistocene glacial and postglacial history of northernmost Ungava (Canada) from Pingualuit Crater Lake sediments   /   Guyard, H.   St-Onge, G.   Pienitz, R.   Francus, P.   Zolitschka, B.   Clarke, G.K.C.   Hausmann, S.   Salonen, V.-P.   Lajeunesse, P.   Ledoux, G.   Lamothe, M.
(Quaternary science reviews, v. 30, no. 27-28, Dec. 2011, p.3892-3907, ill., maps)
References.
ASTIS record 75476.
Languages: English
Web: doi:10.1016/j.quascirev.2011.10.002
Libraries: ACU

The Pingualuit Crater was formed by a meteoritic impact ca. 1.4 million years ago in northernmost Ungava (Canada). Due to its geographical position near the center of successive North American ice sheets and its favorable morphometry, the Pingualuit Crater Lake (water depth = 246 m) promises to yield a unique continuous sedimentary sequence covering several glacial/interglacial cycles in the terrestrial Canadian Arctic. In this paper, we suggest the existence of a subglacial lake at least during the Last Glacial Maximum (LGM) by hydraulic potential modeling using LGM ice-surface elevation and bed topography derived from a digital elevation model. These results support the hypothesis that the bottom sediments of the Crater Lake escaped glacial erosion and may contain a long-term continental sedimentary sequence. We also present the stratigraphy of a 9 m-long core retrieved from the deep basin of the lake as well as a multiproxy reconstruction of its deglacial and postglacial history. The base of the core is formed by very dense diamicton reflecting basal melt-out environments marking the end of subglacial conditions at the coring site. The overlying finely laminated silt are related to the onset of proglacial conditions characterized by extremely low lacustrine productivity. Infra Red Stimulated Luminescence and AMS 14C dating, as well as biostratigraphic data indicate sediment mixing between recent (e.g. Holocene) and much older (pre- to mid-Wisconsinan) material reworked by glacier activity. This process prevents the precise dating of these sediments that we interpret as being deposited just before the final deglaciation of the lake. Two finer grained and organic-rich intervals reflect the inception of lacustrine productivity resulting from the cessation of glacial meltwater inputs and ice-free periods. The lower organic interval corresponds to the early postglacial period (6850-5750 cal BP) and marks the transition between proglacial and postglacial conditions during the Holocene Thermal Maximum, while the uppermost organic-rich core section represents late Holocene sediments (~4200-600 cal BP). The organic intervals are separated by a basin-scale erosive slide occurring around 4200 cal BP and likely related to 1) a seismic event due to the glacio-isostatic rebound following the last deglaciation or 2) slope instabilities associated with rapid discharge events of the lake. (Au)

A, B, F, E, J, H
Bottom sediments; Climate change; Cores; Craters; Deglaciation; Flow; Geochemistry; Glacial epoch; Glacial geology; Glaciation; Glacier lakes; Ice sheets; Lakes; Laurentide Ice Sheet; Mass wasting; Meteorites; Palaeoclimatology; Palaeoecology; Palaeogeography; Palynology; Pleistocene epoch; Primary production (Biology); Radiocarbon dating; Recent epoch; Sedimentation; Shorelines; Sonar; Stratigraphy; Water level

G0826
Laflamme, Lac, Québec; Laflamme, Lac, region, Québec; Pingualuk, Lac, Québec; Pingualuk, Lac, region, Québec


Slow surge of Trapridge Glacier, Yukon Territory, Canada   /   Frappé, T.-P.   Clarke, G.K.C.
(Journal of geophysical research, v.112, no. 3, F03S32, July 2007, 17 p., ill., maps)
Appendix.
References.
ASTIS record 66434.
Languages: English
Web: doi:10.1029/2006JF000607
Libraries: ACU

Trapridge Glacier, a polythermal surge-type glacier located in the St. Elias Mountains, Yukon Territory, Canada, passed through a complete surge cycle between 1951 and 2005. Air photos (1951-1981) and ground-based optical surveys (1969-2005) are used to quantify the modifications in flow and geometry that occurred over this period. Yearly averaged flow records suggest that the active phase began ~1980, and lasted until ~2000. The average velocity in the central area of the glacier went from 16 m/yr in 1974 to 39 m/yr in 1980; it peaked at 42 m/yr in 1984, and remained above 25 m/yr until 2001. Over that interval, the flow decelerated by steps, in 4-year pulses. After a particularly vigorous acceleration in 1997-1999, the glacier gradually slowed to presurge velocities. In 2005, the flow was less than 9 m/yr. Digital elevation models are generated by stereographic analysis of air photos for 1951, 1970, 1972, 1977, and 1981. These models are updated annually using ground-based survey data and a novel implementation of Bayesian kriging. Over the course of the surge, the front of active ice advanced 450 m and the glacier area increased by 10%, with an associated thinning of the ice. The previous surge of Trapridge Glacier, starting before 1939 and ending before 1951, led to a terminus advance of ~1 km. Comparison of the two surges suggests that the 1930s surge started with a slow progression similar to what we observed in the 1980s and 1990s, and switched to a faster flow mode after 1941. This second phase was never attained in the recent surge, probably owing to a lack of mass. (Au)

F
Aerial photography; Flow; Glacier surges; Glacier variations; Glaciers; Instruments; Mass balance; Mathematical models; Measurement; Temporal variations; Thermal regimes; Thickness; Topography; Velocity

G0811, G06
Trapridge Glacier, Yukon; Variegated Glacier, Alaska


Discrimination of the flow law for subglacial sediment using in situ measurements and an interpretation model   /   Kavanaugh, J.L.   Clarke, G.K.C.
(Journal of geophysical research, v.111, no. F1, F01002, Jan. 2006, ill., maps)
Appendix.
References.
ASTIS record 62178.
Languages: English
Web: doi:10.1029/2005JF000346
Libraries: ACU

Subglacial hydrological and mechanical processes play a critical role in determining the flow characteristics and stability of glaciers and ice sheets. To study these processes, we have measured simultaneously basal water pressure, pore water pressure, sediment deformation, glacier sliding, and sediment strength beneath Trapridge Glacier, Yukon Territory, Canada. To interpret these data, we have developed a simple hydromechanical model of processes beneath a soft-bedded alpine glacier. The glacier bed is divided into soft-bedded regions that are hydraulically connected to the subglacial drainage system, soft-bedded but hydraulically unconnected regions, and hard-bedded regions. Each region is represented as a one-dimensional column. The columns are coupled by a simple ice dynamics model that accounts for water-pressure-driven changes in basal shear stress distribution. Synthetic responses for subglacial instruments are calculated from the modeled basal conditions, providing a framework for improving interpretation of field records. The model is used to determine which of several till flow laws best represents conditions beneath Trapridge Glacier. Investigated are linear-viscous, nonlinear-viscous, nonlinear-Bingham, and Coulomb-plastic tills. Pore water pressures, sediment deformation profiles, and sliding rates are calculated for each flow law. Comparison of synthetic and field instrument responses suggests that till behavior is best represented as Coulomb-plastic. Model results also suggest that the ploughmeter is the most diagnostic in situ indicator of till behavior currently available and that using long-term observations of sediment deformation profiles in regions of varying pore water pressure can result in an underestimation of flow law nonlinearity. (Au)

F, B
Deformation; Diurnal variations; Drainage; Flow; Glacial deposits; Glaciers; Glaciology; Hydrology; Instruments; Interstitial water; Mathematical models; Measurement; Mechanical properties; Neutral stress; Plasticity; Sediments (Geology); Spatial distribution; Strain; Strength; Stress; Temporal variations; Viscosity

G0811
Trapridge Glacier, Yukon


Subglacial processes   /   Clarke, G.K.C.
(Annual review of earth and planetary sciences, v. 33, Jan. 2005, p. 247-276, ill., maps)
References.
ASTIS record 62176.
Languages: English
Web: doi:10.1146/annurev.earth.33.092203.122621
Libraries: ACU

Processes operating beneath glaciers can have a greater influence on flow dynamics than those operating within them. The variety and complexity of these processes, which involve interactions among ice, water, and geological solids, resist efforts to establish simple truths and can lead to surprising outcomes. Thermal conditions at the ice-bed interface (melting or nonmelting) and the mechanical properties of the glacier substrate (soft or hard) determine which processes can be activated. The warm-soft case supports the greatest variety of processes and is the most important for fast-flow dynamics and for the mobilization of subglacial sediment. Process interactions can lead to oscillations and spatio-temporal switching behavior in glaciers and ice sheets as well as to the generation of subglacial landforms. (Au)

F, A, B, C
Boreholes; Cores; Creep; Deformation; Drainage; Drumlins; Flow; Friction; Frost heaving; Glacial deposits; Glacial geology; Glacial landforms; Glacial melt waters; Glacier surges; Glaciers; Glaciology; Hydrology; Instruments; Interstitial water; Measurement; Melting; Moraines; Physical properties; Plasticity; Sediments (Geology); Slopes; Soil consolidation; Soil mechanics; Soils; Spatial distribution; Strain; Strength; Stress; Temperature; Temporal variations; Thermal properties; Thermal regimes; Thickness; Velocity; Viscosity; Water

G15, G13, G0811, G06
Alaska; Antarctic Peninsula; Sweden; Trapridge Glacier, Yukon


Hydraulics of subglacial outburst floods : new insights from the Spring-Hutter formulation   /   Clarke, G.K.C.
(Journal of glaciology, v. 49, no.165, 2003, p. 299-313, ill.)
References.
Appendices.
ASTIS record 69999.
Languages: English
Web: doi:10.3189/172756503781830728
Libraries: ACU

Using a slightly modified form of the Spring-Hutter equations, glacial outburst floods are simulated from three classic sites, "Hazard Lake", Yukon, Canada; Summit Lake, British Columbia, Canada; and Grimsvötn, Iceland, in order to calibrate the hydraulic roughness associated with subglacial conduits. Previous work has suggested that the Manning roughness of the conduits is remarkably high, hut the new calibration yields substantially lower values that are representative of those for natural streams and rivers. The discrepancy can be traced to a poor assumption about the effectiveness of heat transfer at the conduit walls. The simulations reveal behaviour that cannot lie inferred from simplified theories: (1) During flood onset, water pressure over much of the conduit can exceed the confining pressure of surrounding ice. (2) Local values of fluid potential gradient can differ substantially from the value averaged over the length of the conduit, contradicting an assumption of simple theories. (3) As the flood progresses, the location of flow constrictions that effectively control the flood magnitude can jump rapidly over large distances. (4) Predicted water temperature at the conduit outlet exceeds that suggested by measurements of exit water temperature. (Au)

F
Flood forecasting; Floods; Flow; Fluid mechanics; Friction; Glacier lake outbursts; Glacier lakes; Glaciers; Groundwater; Heat transmission; Hydrology; Mathematical models; Melting; Physical properties; River discharges; Stress; Surface properties; Temperature; Temporal variations; Topography; Velocity; Water

G0811, G0821, G13
Grimsvötn, Iceland; Hazard Lake, Yukon; Summit Lake (58 39 N, 124 38 W), British Columbia


Glacial control of water resource and related environmental responses to climatic warming : empirical analysis using historical streamflow data from northwestern Canada   /   Fleming, S.W.   Clarke, G.K.C.
(Canadian water resources journal, v. 28, no. 1, Mar. 2003, p. 69-86, ill., maps)
References.
ASTIS record 69992.
Languages: English
Web: doi:10.4296/cwrj2801069
Libraries: ACU

We applied nonparametric statistical techniques to historical streamflow data from five glacierized and four nonglacierized watersheds in southwest Yukon and northwestern British Columbia, Canada, to determine whether rivers with and without catchment glacial cover respond in significantly different ways to a warming climate. The analysis was posed in terms of contrasts between the two groups with respect to long-term trends in annual time series of total river flow volume. We found that glacier-fed rivers grew larger and nival streams progressively smaller over the historical record under an observed regional warming trend. Although some of these trend effects are subtle, the overall result was statistically significant at restrictive confidence levels. Combined consideration of hydrological, meteorological and glaciological trends suggests that the streamflow consequences of increasing temperature exceed those from a concurrent rise in precipitation in the study area, causing increases in both glacial meltwater production and evapotranspiration; the former appears to have the dominant net hydrologic effect in glacierized catchments, and the latter in glacier-free watersheds. By empirically demonstrating that catchment glacial cover can result in opposite trends in total annual flow volume from river to river within an otherwise hydroclimatologically uniform area, the analysis presents strong evidence that climatic warming can materially affect downstream water resources specifically via glaciological pathways, and also implies that regional generalizations of interpreted or projected hydrologic trends may not be tenable in variably-glacierized regions. (Au)

F, E, J, V, N
Climate change; Diurnal variations; Drainage; Effects of climate on ice; Environmental impacts; Flow; Glacial melt waters; Glaciers; Glaciology; Groundwater; Hydrological stations; Hydrology; Mass balance; Mathematical models; Meteorology; Numeric databases; River discharges; Rivers; Runoff; Seasonal variations; Snow hydrology; Storms; Stream flow; Temporal variations; Water resources; Watersheds

G0811, G0821
Alsek River, Alaska/British Columbia/Yukon; Big Creek (62 37 N, 137 00 W), Yukon; British Columbia, Northern; Dezadeash River, Yukon; Kluane River, Yukon; M'Clintock River, Yukon; Takhini River, Yukon; Wann River, British Columbia; Wheaton River, Yukon; White River, Alaska/Yukon; Yukon


Superlakes, megafloods, and abrupt climate change   /   Clarke, G.K.C.   Leverington, D.   Teller, J.   Dyke, A.
(Science, v.301, no.5635, 15 Aug. 2003, p. 922-923, ill., 1 map)
References.
ASTIS record 53653.
Languages: English
Web: doi:10.1126/science.1085921
Libraries: ACU

As concern about the magnitude and rate of future climate change looms, it becomes increasingly important to understand the mechanisms underlying past abrupt climate change events. A cold event that occurred 8200 years ago, although much less extreme than some events during the Ice Ages, is probably most amenable to detailed examination because it is the most recent such event. According to the ice-core record from Greenland, the abrupt cooling 8200 years ago was the largest climate excursion of the past 10,000 years ...: The mean temperature dropped by about 5°C for about 200 years ..., snow accumulation decreased sharply, precipitation of chemical impurities increased, and forest fires became more frequent. The event, which affected much of the Northern Hemisphere ..., appears to have been triggered by the sudden release of fresh water from a huge, glacier-dammed lake that had formed during the deglaciation of North America. ... To explain the 8200-year cold event, a search for large sources of fresh water is thus a good starting point. ... Shortly before the Laurentide Ice Sheet finally disintegrated, the glacial lake- Lake Agassiz- had become a superlake (see the figure, B). ... The ultimate release of Lake Agassiz waters to Hudson Bay was unavoidable. On the basis of radiocarbon dating, the outburst occurred 8450 years ago .... The 8200-year cold event was thus most likely triggered by a flood of fresh water from super-lake Agassiz that flowed northward through Hudson Bay into the North Atlantic. ... Marine sediments provide clear evidence for the 8200-year cold event ... but are equivocal about changes in ocean circulation that may have accompanied it. The response of the North Atlantic circulation to injection of fresh water into the Labrador Sea has been explored with a coupled ocean-atmosphere-sea ice model ... in which a fixed volume of fresh water was released to the Labrador Sea at a steady rate over intervals of 10 to 50 years. All simulations show a weakening of the thermohaline circulation in the Nordic Seas in response to freshwater input. For some simulations, the recovery time is greater than 200 years. However, the released water volume in the model exceeds a recent estimate ... of maximum lake volume by a factor of ~3, and the rate of release differs from the sharp pulse of less than 1 year duration suggested by flood modeling .... Much remains unknown about the 8200-year cold event. Further studies of how ice sheet margins, oceans, and vegetation zones were affected will help us to understand the cascade of responses that followed the initial outburst. Geological and geophysical studies in the Hudson Bay region and Labrador Sea could determine where the water release occurred and whether it took place as one or multiple events. ... (Au)

B, F, E, G
Bottom sediments; Climate change; Cores; Deglaciation; Floods; Geophysics; Glacial geology; Glacial melt waters; Glacier lake outbursts; Glacier lakes; Ice sheets; Mathematical models; Melting; Ocean currents; Ocean-atmosphere interaction; Palaeoclimatology; Radiocarbon dating; Runoff; Sea ice; Sea level

G11, G10, G0814, G09, G0813, G0826
Greenland; Hudson Bay; Hudson Bay region; Labrador Sea; North Atlantic Ocean; Nunatsiavut, Labrador; Ungava, Baie d', region, Québec


Autoregressive noise, deserialization, and trend detection and quantification in annual river discharge time series   /   Fleming, S.W.   Clarke, G.K.C.
(Canadian water resources journal, v. 27, no. 3, Sept. 2002, p. 335-354, ill.)
References.
ASTIS record 69990.
Languages: English
Web: doi:10.4296/cwrj2703335
Libraries: ACU

The evaluation of long-term trends in yearly discharge records, such as annual peak daily flow or total annual runoff, is important to a variety of issues including water resource planning, flood hazard studies, and the assessment of historical data for evidence of anthropogenic climate change effects. Prewhitening or deserialization procedures have recently been developed and applied to adjust statistical tests of monotonic trend, and the nonparametric Mann-Kendall test in particular, for sensitivity to serial dependence. Deserialization attributes much or all of the observed serial correlation in a time series to an autoregressive process; however, deterministic processes can also lead to a large lag-1 serial correlation coefficient, and the physical basis for autoregressive noise may be weaker for annual rather than more finely-discretized (e.g., daily) streamflow records. In this paper, the potential consequences of using such procedures are investigated through a suite of Monte Carlo simulations. We find that prewhitening can substantially and inappropriately reduce the power of trend significance tests and increase slope estimate errors. The choice of whether deserialization is applied is to some degree left to the judgement and conservatism of the individual practitioner. We suggest that such procedures not be applied to a given annual hydrologic time series unless there is a strong site-specific physical basis for the assumption of AR(1) noise and that if deserialization is performed, very recently-developed multi-stage techniques appear preferable. We also present a number of useful ancillary results regarding trend identification in streamflow-derived data. (Au)

F, E, J, V
Climate change; Diurnal variations; Drainage; Environmental impacts; Flow; Groundwater; Hydrography; Hydrological stations; Hydrology; Mass balance; Mathematical models; Numeric databases; River discharges; Rivers; Runoff; Seasonal variations; Storms; Stream flow; Temporal variations

G0811
Yukon River, Alaska/Yukon


A multicomponent coupled model of glacier hydrology : 2. application to Trapridge Glacier, Yukon, Canada   /   Flowers, G.E.   Clarke, G.K.C.
(Journal of geophysical research, v.107, no. B11, 2288, Nov. 2002, p.ECV 10-1 - ECV 10-16, ill., map)
References.
ASTIS record 69986.
Languages: English
Web: doi:10.1029/2001JB001124
Libraries: ACU

A new glaciohydraulic model is tailored to Trapridge Glacier, Yukon, Canada, where long-term measurements of subglacial water pressure provide parameter constraints and a platform for model evaluation. Using digital elevation models and meteorological data as input, we investigate hydrology on diurnal and seasonal timescales. Quantitative comparisons of simulated and observed pressure records allow us to select a reference model objectively, from which we gain first insights into the gross spatial characteristics of the drainage system. Equilibrium simulations highlight target areas for water storage and potential sticky spots, both of which have established relevance to glacier dynamics. Seasonal simulations capture the key signatures of spring and autumn transitions and corroborate our understanding of the processes involved. Successfully modeled features of the spring transition include increased hydraulic coupling between the surface and bed with time, temporary augmentation of subglacial storage, and rapid subglacial transitions from a hydraulically unconnected to connected state. Autumn transitions are characterized by deterioration of the basal drainage network, drawdown of subglacial storage reservoirs, and heightened sensitivity to precipitation and surface refreezing. Finally, we draw attention to the important role of groundwater transport in cold glacial environments where permafrost can impede drainage from the ice margin. (Au)

F, E, C
Ablation; Aquifers; Crevasses; Diurnal variations; Drainage; Energy budgets; Flow; Glacial melt waters; Glacier surges; Glaciers; Groundwater; Hydrology; Mass balance; Mathematical models; Measurement; Meteorology; Permafrost; Physical properties; River discharges; Runoff; Seasonal variations; Slopes; Snow; Solar radiation; Topography

G0811
Trapridge Glacier, Yukon


A multicomponent coupled model of glacier hydrology : 1. theory and synthetic examples   /   Flowers, G.E.   Clarke, G.K.C.
(Journal of geophysical research, v.107, no. B11, 2287, Nov. 2002, p.ECV 9-1 - ECV 9-17, ill.)
References.
ASTIS record 69985.
Languages: English
Web: doi:10.1029/2001JB001122
Libraries: ACU

[1] Basal hydrology is acknowledged as a fundamental control on glacier dynamics, especially in cases where surface meltwater reaches the bed. For many glaciers at midlatitudes, basal drainage is influenced by subaerial, englacial, and subsurface water flow. One of the major shortcomings of existing basal hydrology models is the treatment of the glacier bed as an isolated system. We present theoretical and computational models that couple glacier surface runoff, englacial water storage and transport, subglacial drainage, and subsurface groundwater flow. Each of the four model components is represented as a two-dimensional, vertically integrated layer that communicates with its neighbors through water exchange. Governing equations are derived from the law of mass conservation and are expressed as a balance between the internal distribution of water and external sources. The numerical exposition of this theory is a time-dependent finite difference model that can be used to simulate glacier drainage. In this paper we outline the theory and conduct simple tests using an idealized glacier geometry. In the companion paper, the model is tailored to Trapridge Glacier, Yukon Territory, Canada, where results are compared with measurements of subglacial water pressure. (Au)

F
Ablation; Aquifers; Crevasses; Diurnal variations; Drainage; Flow; Glacial melt waters; Glaciers; Groundwater; Hydrology; Mass balance; Mathematical models; Measurement; Physical properties; River discharges; Runoff; Topography

G0811
Trapridge Glacier, Yukon


Glaciers of the St. Elias Mountains   /   Clarke, G.K.C.   Holdsworth, G.
(Glaciers of North America / Edited by Richard S. Williams and Jane G. Ferrigno. U.S. Geological Survey professional paper, 1386-J-1, 2002, p.J301-J312, ill., 1 map)
References.
With a section on Quantitative Measurements of Tweedsmuir Glacier and Lowell Glacier Imagery by Gerald Holdsworth, Philip J. Howarth, and C. Simon L. Ommanney, ASTIS record 53253.
ASTIS record 53252.
Languages: English
Libraries: ACU

The St. Elias Mountains region of Canada is made up of a series of mountain ranges that contain a particularly wide variety of glacier types, defined both morphologically and thermally. This variety is a result of the extreme topography, which has a maximum relief of 4,200 meters within a few kilometers, coupled with the large gradients recorded in precipitation and temperature throughout the ranges. Glacier types seen here are valley glaciers, high-elevation plateau glaciers, ice fields and associated outlet glaciers, and piedmont glaciers of different shapes and sizes. Glacier lengths range from about a kilometer to more than 70 kilometers (Hubbard Glacier, which ends in Alaska, has a length of 72 kilometers in Canada and a total length of 112 kilometers); their areas range from a few square kilometers to more than 1,200 square kilometers for Seward Glacier. Temperate glaciers are common at low elevations, particularly on the Pacific Ocean side of the axis (drainage divide). Subpolar glaciers are present on the north (continental) side of the axis even at low elevations. Cold glaciers, at "polar" temperatures, exist on high-elevation plateaus such as on Mount Logan (5,956 meters). The presence of a large concentration of generally subpolar surging glaciers in the region is particularly noteworthy. This topic receives the most attention here because features diagnostic of surges are easily detected on satellite images, from which time-series measurements, related to the dynamics of the glacier, may be made, as shown for Tweedsmuir Glacier and Lowell Glacier. (Au)

F, A
Aerial photography; Arctic Institute of North America. Icefield Ranges Research Project; Drainage; Glacial melt waters; Glacier lake outbursts; Glacier lakes; Glacier surges; Glaciers; Hydrology; Mountains; Remote sensing; Research; River discharges; Rivers; Satellite photography; Valleys

G0811, G0821, G06
Alsek River region, Alaska/British Columbia/Yukon; Chitina River region, Alaska; Donjek River region, Yukon; Lowell Glacier, Yukon; Slims River region, Yukon; St. Elias Mountains, Alaska/British Columbia/Yukon; Tweedsmuir Glacier, British Columbia/Yukon; White River region, Alaska/Yukon


Glaciers of the Coast Mountains   /   Clarke, G.K.C.   Holdsworth, G.
(Glaciers of North America / Edited by Richard S. Williams and Jane G. Ferrigno. U.S. Geological Survey professional paper, 1386-J-1, 2002, p.J291-J300, ill., 1 map)
References.
ASTIS record 53251.
Languages: English
Libraries: ACU

The Coast Mountains follow the Pacific coast of Canada and extend from southwestern British Columbia to southwestern Yukon Territory. The predominantly granitic bedrock forms elevated blocks that have been deeply dissected by erosion, yielding a distinctive pattern of disjointed highland ice fields that are drained by radiating outlet glaciers. Popular interest in the glaciers of the Coast Mountains centers on the hazards and problems that they engender and on their attractions as a recreational resource. Scientific interest has largely focused on their status as climate indicators. We touch on these various themes by discussing the glacier-associated problems of the Granduc mining operation near Leduc Glacier in northwestern British Columbia, the outburst floods of glacier-dammed Flood Lake, and the recreational and scientific roles of small glaciers in Garibaldi Provincial Park near Vancouver, British Columbia. (Au)

F, P, L, S, E
Climate change; Drainage; Effects of climate on ice; Environmental impacts; Glacier lake outbursts; Glacier lakes; Glaciers; Glaciology; Location; Mapping; Mass balance; Measurement; Mining; Ores; Outdoor recreation; Parks; Remote sensing; Research; SAR; Satellite photography; Tunnels

G0811, G0821
British Columbia; Leduc Glacier, British Columbia; Yukon


Hydrochemical coupling of a glacial borehole-aquifer system   /   Oldenborger, G.A.   Clarke, G.K.C.   Hildes, D.H.D.
(Journal of glaciology, v. 48, no.162, 2002, p. 357-368, ill.)
Appendix.
References.
ASTIS record 51951.
Languages: English
Web: doi:10.3189/172756502781831232
Libraries: ACU

Measurements of the electrical conductivity of subglacial water provide a useful complement to measurements of pressure and turbidity. In the summer season, fluctuations of conductivity can be attributed to changes in water transport, water provenance and subglacial residence time. These explanations are unlikely to apply during the winter season because surface melt sources are not active and the subglacial water system is predominantly unconnected. Thus, fluctuations in water conductivity during the winter months seem paradoxical. To introduce a quantitative basis for comprehending such phenomena, we develop an interpretative model of the hydrochemical interaction between a water-filled borehole and a subglacial aquifer. The electrical conductivity of water near the borehole-aquifer contact is affected not only by diffusion but also by advective transport of solute between the two reservoirs in response to pressure forcing of the system. Using records of ice strain, water pressure and electrical conductivity from unconnected boreholes in Trapridge Glacier, we demonstrate that changes in borehole geometry caused by ice-strain events provide a plausible mechanism for at least some of the observed fluctuations of electrical conductivity. Conductivity records provide information regarding advective coupling of the borehole-aquifer system that is not available from pressure records alone. (Au)

F
Aquifers; Boreholes; Boundary layers; Chemical properties; Electrical properties; Glacial melt waters; Glaciers; Heat transmission; Hydrology; Instruments; Mathematical models; Measurement; Permeability; Physical properties; Seasonal variations; Snow; Spatial distribution

G0811
Trapridge Glacier, Yukon


Origin and fate of Lake Vostok water frozen to the base of the East Antarctic ice sheet   /   Bell, R.E.   Studinger, M.   Tikku, A.A.   Clarke, G.K.C.   Gutner, M.M.   Meertens, C.
(Nature, v.416, no.6878, 21 Mar. 2002, p. 307-310, ill., maps)
References.
ASTIS record 51864.
Languages: English
Web: doi:10.1038/416307a
Libraries: ACU

The subglacial Lake Vostok may be a unique reservoir of genetic material and it may contain organisms with distinct adaptations, but it has yet to be explored directly. The lake and the overlying ice sheet are closely linked, as the ice sheet thickness drives the lake circulation, while melting and freezing at the ice sheet base will control the flux of water, biota and sediment through the lake. Here we present a reconstruction of the ice flow trajectories for the Vostok core site, using ice-penetrating radar data and Global Positioning System (GPS) measurements of surface ice velocity. We find that the ice sheet has a significant along-lake flow component, persistent since the Last Glacial Maximum. The rates at which ice is frozen (accreted) to the base of the ice sheet are greatest at the shorelines, and the accreted ice layer is subsequently transported out of the lake. Using these new flow field and velocity measurements, we estimate the time for ice to traverse Lake Vostok to be 16,000 - 20,000 years. We infer that most Vostok ice analysed to date was accreted to the ice sheet close to the western shoreline, and is therefore not representative of open lake conditions. From the amount of accreted lake water we estimate to be exported along the southern shoreline, the lake water residence time is about 13,300 years. (Au)

F, A, B
Accumulation; Aerial surveys; Chemical properties; Composition; Electrical properties; Flow; Geographical positioning systems; Geological time; Glacial epoch; Glacial melt waters; Glacial stratigraphy; Glacial transport; Glacier lakes; Ice sheets; Impurities; Physical properties; Radar; Recent epoch; Shorelines; Thickness; Topography; Velocity

G15
East Antarctica; Vostok, Lake, Antarctic regions


Modelling subglacial erosion and englacial sediment transport of the North American ice sheets   /   Hildes, D.H.D.   Clarke, G.K.C. [Supervisor]
Vancouver, B.C. : University of British Columbia, 2001.
xviii, 149 p. : ill., maps ; 28 cm.
(ProQuest Dissertations & Theses publication, no. NQ73179)
ISBN 0-612-73179-0
Thesis (Ph.D.) - University of British Columbia, Vancouver, B.C., 2001.
Indexed from a PDF file acquired from ProQuest Dissertations & Theses.
Appendices.
References.
ASTIS record 57012.
Languages: English
Libraries: OONL

The glacial geology of North America is a rich resource upon which reconstructions of ice sheets are made. Numerical modelling of ice sheets based on ice physics is an alternate avenue for cryospheric reconstruction. However, such algorithms are unable to draw from the full wealth of geomorphic data because a large-scale forward model of basal processes, necessary to link the ice and the bed, is not available. I develop a process-based model of sediment production, entrainment, deposition and transport to fill this conspicuous gap. Subglacial abrasion is modelled following Hallet [1979, 1981] and a quarrying model, dependent on subcritical crack growth, is constructed. Entrainment proceeds predominantly by intrusion into the sediment [Iverson and Semmens, 1995] and when basal melt exceeds the rate of entrainment, englacial sediment is deposited. Both vertical redistribution of englacial sediment within an ice column and lateral transport of debris is considered. Ice entrains loose debris from the bed, transports it downstream and deposits an allochthonous debris train, observable on the modern landscape. This can be modelled when an accurate geologic representation of the bed is used, allowing the exploitation of distinct lithologies as natural tracers of ice motion. Also, incorporation of the differences in physical properties between various lithologies is possible with such a lithologically realistic description of the bed. Several processes are functions of bed topography and a description of small-scale topography within a large-scale grid is required; a downscaling method is therefore developed. Basal-ice processes must be coupled to both ice sheet conditions and subglacial hydrology. The Marshall-Clarke thermo-mechanical ice sheet model [Marshall, 1996; Marshall and Clarke, 1997a,b; Marshall et al., 2000] gives the necessary ice sheet fields and provides the forcing for the hydrology model of Flowers [2000] which in turn delivers subglacial water pressure, used for both the quarrying and entrainment simulations. Comparisons of model results with the documented large-scale debris trains of Hudson Bay Paleozoic sedimentary rocks and Dubawnt Group detritus are used to test the veracity of the transport model while estimates of paleo-erosion are used to assess the erosion model. (Au)

B, A, F, E
Carbonates; Climate change; Cores; Glacial deposits; Glacial epoch; Glacial erosion; Glacial geology; Glacial landforms; Glacial melt waters; Hydrology; Ice sheets; Intrusions (Geology); Mapping; Mathematical models; Moraines; Oxygen-18; Palaeoclimatology; Palaeogeography; Pleistocene epoch; Sediment transport; Sedimentation; Sediments (Geology); Theses; Topography

G081
Canadian Arctic; Hudson Bay region; Kaskawulsh Glacier, Yukon; Nunavik, Québec; Trapridge Glacier, Yukon


Review of subglacial hydro-mechanical coupling : Trapridge Glacier, Yukon Territory, Canada   /   Fischer, U.H.   Clarke, G.K.C.
(Quaternary international, v. 86, no. 1, Dec. 2001, p. 29-43, ill., map)
References.
ASTIS record 53356.
Languages: English
Web: doi:10.1016/S1040-6182(01)00049-0
Libraries: ACU

The interaction of basal processes with the subglacial drainage system is a critical issue in understanding glacier dynamics. Since the recognition that many glaciers and ice masses overlie soft sediments rather than hard bedrock, much research has been undertaken to investigate how mechanical and hydrological conditions of a deformable substrate control the coupling at the ice-bed interface and thus affect fast ice flow and glacier surging. In research undertaken on Trapridge Glacier, a small surge-type glacier in the St. Elias Mountains, Yukon Territory, Canada, we have combined extensive field investigations using novel measurement techniques and theoretical modelling to study hydro-mechanical coupling processes. Measurements of subglacial water pressure indicate that the basal water system can be dramatically inhomogeneous, both spatially and temporally. Since ice-bed coupling is strongly influenced by subglacial water pressure, the stresses at the bed are also markedly heterogeneous and are expected to form a patchwork distribution which mimics the pressure distribution of the basal water system. This heterogeneity in the stress field at the ice-bed interface introduces a pronounced variability to the basal motion mechanics. As such, basal sliding and subglacial sediment deformation are not steady and continuous processes. Instead, the variability of the subglacial water system leads to a spatial and temporal interplay of increased ice-bed coupling at low water pressures at one site or time with ice-bed decoupling during rising water pressures at other sites or times. Thus, on the one hand there is downglacier shear deformation of the bed and accumulation of elastic strain in ice and sediment, while on the other hand there is enhanced slip-sliding of the glacier and upglacier shear motion of the bed due to an elastic relaxation of the sediment. (Au)

F, B
Ablation; Deformation; Drainage; Flow; Glacier surges; Glaciers; Instruments; Mathematical models; Measurement; Mechanical properties; Neutral stress; Sediments (Geology); Strain; Temporal variations; Velocity; Viscosity

G0811
Trapridge Glacier, Yukon


Abrupt glacier motion and reorganization of basal shear stress following the establishment of a connected drainage system   /   Kavanaugh, J.L.   Clarke, G.K.C.
(Journal of glaciology, v. 47, no.158, 2001, p. 472-480, ill., 1 map)
References.
ASTIS record 50643.
Languages: English
Web: doi:10.3189/172756501781831972
Libraries: ACU

Three episodes of strong basal motion occurred at Trapridge Glacier, Yukon Territory, Canada, on 11 June 1995 following the establishment of a connected subglacial drainage system. Responses to these "spring events" are noted in the records for 42 instruments and were recorded throughout the ~60 000 m² study area. Strong basal motion during the events is indicated by ploughmeter load-bolt and vertical-strain records, and abrupt pressure changes in several transducer records denote damage caused by extreme pressure pulses. These pressure pulses, generated by the abrupt basal motion, also resulted in the failure of seven pressure sensors. Records for pressure, turbidity and conductivity sensors indicate that basal drainage patterns did not change significantly during the events. Geophone records suggest that the episodes of basal motion were precipitated by the gradual failure of a "sticky spot" following hydraulic connection of part of the study area. This failure resulted in the transfer of basal stress to the unconnected region of the bed during the course of the events. No evidence for strong basal motion is seen in the instrument records for several weeks following the events, suggesting that the mechanical adjustments resulted in a stable configuration of basal stresses. This event illustrates how unstable situations can be quickly accommodated by mechanical adjustments at the glacier bed. (Au)

F, B
Boreholes; Deformation; Drainage; Flow; Glacial melt waters; Glacier surges; Glaciers; Instruments; Measurement; Melting; Movement; Neutral stress; Sediments (Geology); Stress

G0811
Trapridge Glacier, Yukon


Hydromechanical behaviour of a surge-type glacier : Trapridge Glacier, Yukon Territory, Canada   /   Kavanaugh, J.L.   Clarke, G.K.C. [Supervisor]
Vancouver, B.C. : University of British Columbia, 2000.
xvi, 157 p. : ill., maps ; 28 cm.
(ProQuest Dissertations & Theses publication, no. NQ61125)
ISBN 0-612-61125-6
References.
Thesis (Ph.D.) - University of British Columbia, Vancouver, B.C., 2000.
Indexed from a PDF file acquired from ProQuest Dissertations & Theses.
ASTIS record 55329.
Languages: English
Libraries: OONL

Subglacial hydrological and mechanical processes play a critical role in determining the flow characteristics and stability of glaciers and ice sheets, but our understanding of these processes remains incomplete. Instrument and modelling studies of conditions beneath Trapridge Glacier, a small surge-type glacier in the St. Elias Mountains, Yukon Territory, Canada, yield additional insight into subglacial hydromechanical behaviour. High-pressure pulses in the subglacial drainage system are indicated by sudden offsets in measured pressure and result from damage to the pressure sensor measurement diaphragm. Laboratory and modelling studies confirm that pressures significantly above the transducer rating produce offsets comparable to those observed in field records. Instrument records suggest that high-pressure pulses are generated by abrupt glacier motion that compresses or dilates the subglacial hydraulic system. Analysis of instrument records taken during summer 1995 reveals that a series of hydromechanical events occurred following the establishment of a subglacial drainage system. Pressure fluctuations in this drainage system weakened a basal region that was acting as a pinning point, resulting in three episodes of strong basal motion. I develop a simple hydromechanical model of basal processes acting beneath a soft-bedded alpine glacier. In this model, I classify the glacier bed into three regions: soft-bedded and hydraulically-connected to the subglacial drainage system, soft-bedded and unconnected and hard-bedded. Each basal region is modelled as a one-dimensional column. The time evolution of pore-water pressure, till dilatancy, sediment deformation and glacier sliding is calculated in soft-bedded regions; hard-bedded regions are considered rigid and impermeable. The regions are coupled by a simple ice-dynamics model. Sediment deformation is calculated for four till flow laws: linear-viscous, nonlinear-viscous, nonlinear-Bingham and Coulomb-plastic. I develop relations describing instrument responses to modelled subglacial basal conditions. I apply the hydromechanical model to simulate typical summer conditions beneath Trapridge Glacier. Modelled pore-water pressure profiles, deformation profiles, basal shear stress and instrument responses are presented for the four flow laws. Comparison of synthetic and field instrument responses suggests that till behaviour is best represented as Coulomb-plastic. (Au)

F, B, E, C
Atmospheric temperature; Boreholes; Deformation; Density; Diurnal variations; Drainage; Elasticity; Electrical properties; Flow; Glacial deposits; Glacial melt waters; Glacier surges; Glaciers; Hydrology; Ice sheets; Instruments; Interstitial water; Logistics; Mathematical models; Measurement; Mechanical properties; Melting; Movement; Neutral stress; Permeability; Plasticity; Seasonal variations; Size; Soils; Strain; Stress; Suspended solids; Theses; Thickness

G0811
Trapridge Glacier, Yukon


A multicomponent coupled model of glacier hydrology   /   Flowers, G.E.   Clarke, G.K.C. [Supervisor]
Vancouver, B.C. : University of British Columbia, 2000.
xiii, 265 p. : ill., maps ; 28 cm.
(ProQuest Dissertations & Theses publication, no. NQ61088)
ISBN 0-612-61088-8
Appendices.
References.
Thesis (Ph.D.) - University of British Columbia, Vancouver, B.C., 2000.
Indexed from a PDF file acquired from ProQuest Dissertations & Theses.
ASTIS record 55250.
Languages: English
Libraries: OONL

Multiple lines of evidence suggest a causal link between subglacial hydrology and phenomena such as fast-flowing ice. This evidence includes a measured correlation between water under alpine glaciers and their motion, the presence of saturated sediment beneath Antarctic ice streams, and geologic signatures of enhanced paleo-ice flow over deformable substrates. The complexity of the glacier bed as a three-component mixture presents an obstacle to unraveling these conundra. Inadequate representations of hydrology, in part, prevent us from closing the gap between empirical descriptions and a comprehensive consistent framework for understanding the dynamics of glacierized systems. I have developed a distributed numerical model that solves equations governing glacier surface runoff, englacial water transport, subglacial drainage, and subsurface groundwater flow. Ablation and precipitation drive the surface model through a temperature-index parameterization. Water is permitted to flow over and off the glacier, or to the bed through a system of crevasses, pipes, and fractures. A macroporous sediment horizon transports subglacial water to the ice margin or to an underlying aquifer. Governing equations are derived from the law of mass conservation and are expressed as a balance between the internal redistribution of water and external sources. Each of the four model components is represented as a two-dimensional, vertically-integrated layer that communicates with its neighbors through water exchange. Stacked together, these layers approximate a three-dimensional system. I tailor the model to Trapridge Glacier, where digital maps of the surface and bed have been derived from ice-penetrating radar data. Observations of subglacial water pressure provide additional constraints on model parameters and a basis for comparison of simulations with real data. Three classical idealizations of glacier geometry are used for simple model experiments. Equilibrium tests emphasize geometric controls on hydrology, while time-dependent simulations disclose where and how the input forcing is manipulated by the system. Results of sensitivity tests show good qualitative agreement with the glaciological lore. Using Trapridge Glacier geometry and meteorological observations, I investigate hydrology on sub-hourly, diurnal, and seasonal timescales. Examples from 1990, 1995, and 1997 collectively substantiate the merit of the model in a variety of situations. (Au)

F, E, A
Ablation; Aquifers; Aspect; Atmospheric pressure; Atmospheric temperature; Boreholes; Crevasses; Deformation; Density; Diurnal variations; Drainage; Electronic data processing; Energy budgets; Flow; Fracturing; Glacial deposits; Glacial melt waters; Glacier surges; Glaciers; Groundwater; Heat transmission; Hydrology; Logistics; Mass balance; Mathematical models; Measurement; Melting; Movement; Precipitation (Meteorology); Radar; Runoff; Seasonal variations; Size; Slopes; Snow; Solar radiation; Spatial distribution; Temporal variations; Thermal regimes; Theses; Thickness; Topography; Velocity

G0811
Trapridge Glacier, Yukon


An integrated modelling approach to understanding subglacial hydraulic release events   /   Flowers, G.E.   Clarke, G.K.C.
(Papers from the International Symposium on the Verification of Cryospheric Models, held in Zürich, Switzerland, 16-20 August 1999 / Edited by K. Steffen. Annals of glaciology, v. 31, 2000, p. 222-228, ill.)
References.
ASTIS record 48577.
Languages: English
Web: doi:10.3189/172756400781820471
Libraries: ACU

Outbursts of subglacial water from numerous alpine glaciers have been observed and documented. Such events tend to occur in spring and are thus attributed to an inability of the winter subglacial drainage system (characterized by high water pressure and low capacity) to accommodate a sudden and profuse influx of surface meltwater. Prior to a release event, bursts of glacier motion are common, and the release then precipitates the restoration of summer plumbing that damps or terminates surface acceleration. The events bear witness to the importance of interactions between surface melt, runoff, englacial water storage and internal routing, in addition to subglacial drainage morphology. Using a distributed numerical model to simultaneously solve surficial, englacial and subglacial water-transport equations, we investigate the role of these components in a hydro-mechanical event observed at Trapridge Glacier, Yukon Territory, Canada, in July 1990. (Au)

F, A
Glacial landforms; Glacial melt waters; Glacier lake outbursts; Glaciers; Mathematical models; Runoff

G0811
Trapridge Glacier, Yukon


Evidence for extreme pressure pulses in the subglacial water system   /   Kavanaugh, J.L.   Clarke, G.K.C.
(Journal of glaciology, v. 46, no.153, 2000, p. 206-212, ill., 1 map)
References.
ASTIS record 48534.
Languages: English
Web: doi:10.3189/172756500781832963
Libraries: ACU

A suite of subglacial water-pressure records from the 1996 summer field season at Trapridge Glacier, Yukon Territory, Canada, discloses a hydraulic event that cannot readily be explained by known forcings. We suggest that these records indicate covert failure of the pressure sensors caused by at least one large water-pressure pulse. The sign and magnitude of the pulse appears to have varied spatially and the pulse duration was less than the 2 min sampling interval of our data loggers. Laboratory experiments support this interpretation and indicate that the pulse magnitude exceeded 900 m of hydraulic head, roughly 15 times the ice-overburden pressure. Within glaciers, large water-pressure pulses can be generated when abrupt ice motion changes the volume of the subglacial hydraulic system. (Au)

F
Drainage; Flow; Glacier surges; Glaciers; Glaciology; Hydrology; Instruments; Measurement; Stress

G0811
Trapridge Glacier, Yukon


Glaciological reconstruction of the Laurentide Ice Sheet : physical processes and modelling challenges   /   Marshall, S.J.   Tarasov, L.   Clarke, G.K.C.   Peltier, W.R.
(Canadian journal of earth sciences, v. 37, no. 5, May 2000, p. 769-793, ill., maps)
References.
ASTIS record 48496.
Languages: English
Web: doi:10.1139/cjes-37-5-769
Libraries: ACU

Current understanding of Pleistocene ice-sheet history is based on collective inferences from three separate avenues of study: (1) the geologic and paleoceanographic records, (2) the isostatic record, and (3) the behaviour of contemporary glaciers and ice sheets. The geologic record provides good constraint on the areal extent of former ice sheets, while isostatic deflection patterns provide important information about late-glacial ice-sheet thickness. The picture emerging from geologic and isostatic deductions is suggestive of a thin and mobile Laurentide Ice Sheet relative to present-day Greenland and Antarctica. We model Laurentide Ice Sheet evolution through a glacial cycle to explore the glaciological mechanisms that are required to replicate the geologic and isostatic evidence. A number of glaciological processes important to the ice-sheet evolution are not fully understood, including marine-based ice dynamics, iceberg calving, rheologic properties of ice, and basal flow dynamics. We present a spectrum of glacial cycle simulations with different treatments of poorly constrained physical processes. We conclude that glaciological model reconstructions can only be reconciled with the late-glacial geologic record of a thin, low-sloping Laurentide Ice Sheet by invoking (1) extremely deformable ice, (2) widespread basal flow, or (3) paleoclimate-ice-sheet fluctuations which give last glacial maximum ice sheets that are far from equilibrium. (Au)

B, F, A, J, E, G
Atmospheric temperature; Calving (Ice); Deglaciation; Effects of climate on ice; Effects of ice on climate; Geology; Glaciation; Glaciology; Ice sheets; Icebergs; Laurentide Ice Sheet; Mathematical models; Palaeoclimatology; Palaeogeography; Pleistocene epoch; Precipitation (Meteorology); Sea ice; Sea level; Temperature

G10, G08, G15, G081
Antarctic regions; Canada; Canadian Arctic; Greenland; Hudson Bay region; Hunker Creek region, Yukon; North American Arctic; Nunavik, Québec


Modeling North American freshwater runoff through the last glacial cycle   /   Marshall, S.J.   Clarke, G.K.C.
(Quaternary research, v. 52, no. 3, Nov. 1999, p. 300-315, ill., maps)
References.
ASTIS record 48770.
Languages: English
Web: doi:10.1006/qres.1999.2079
Libraries: ACU

The Northern Hemisphere ice sheets decayed rapidly during deglacial phases of the ice-age cycle, producing meltwater fluxes that may have been of sufficient magnitude to perturb oceanic circulation. The continental record of ice-sheet history is more obscured during the growth and advance of the last great ice sheets, ca. 120,000-20,000 yr B.P., but ice cores tell of high-amplitude, millennial-scale climate fluctuations that prevailed throughout this period. These climatic excursions would have provoked significant fluctuation of ice-sheet margins and runoff variability whenever ice sheets extended to mid-latitudes, giving a complex pattern of freshwater delivery to the oceans. A model of continental surface hydrology is coupled with an ice-dynamics model simulating the last glacial cycle in North America. Meltwater discharged from ice sheets is either channeled down continental drainage pathways or stored temporarily in large systems of proglacial lakes that border the retreating ice-sheet margin. The coupled treatment provides quantitative estimates of the spatial and temporal patterns of freshwater flux to the continental margins. Results imply an intensified surface hydrological environment when ice sheets are present, despite a net decrease in precipitation during glacial periods. Diminished continental evaporation and high levels of meltwater production combine to give mid-latitude runoff values that are highly variable through the glacial cycle, but are two to three times in excess of modern river fluxes; drainage to the North Atlantic via the St. Lawrence, Hudson, and Mississippi River catchments averages 0.356 Sv for the period 60,000-10,000 yr B.P., compared to 0.122 Sv for the past 10,000 yr. High-amplitude meltwater pulses to the Gulf of Mexico, North Atlantic, and North Pacific occur throughout the glacial period, with ice-sheet geometry controlling intricate patterns of freshwater routing variability. Runoff from North America is staged in the final deglaciation, with a stepped sequence of pulses through the Mississippi, St. Lawrence, Arctic, and Hudson Strait drainages. (Au)

A, F, D, E, B
Deglaciation; Drainage; Glacial epoch; Glacial melt waters; Glacier lakes; Hydrology; Ice sheets; Laurentide Ice Sheet; Mass balance; Mathematical models; Ocean currents; Palaeoclimatology; Palaeohydrology; Rivers; Runoff; Spatial distribution; Thickness; Topography

G0812, G081, G0815, G0826, G0825
Baffin Bay-Davis Strait; Canada; Canadian Arctic; Columbia River, Washington; Hudson Strait, Nunavut/Québec; Mackenzie River, N.W.T.; Mississippi River, United States; North America; St. Lawrence River, Canada/United States


Subglacial electrical phenomena   /   Blake, E.W.   Clarke, G.K.C.
(Journal of geophysical research, v.104, no. B 4, Apr. 10, 1999, p.7481-7495, ill.)
References.
ASTIS record 47546.
Languages: English
Web: doi:10.1029/98JB02466
Libraries: ACU

The subglacial electrical environment is surprisingly complex owing to the variety of processes that promote spatial and temporal variability. Possible sources of variability are the chemical evolution of subglacial water and the structural and morphological evolution of the drainage configuration. Such changes contribute to changes in the apparent resistivity of the glacier bed. Less obvious, but possibly more interesting, are those electrical phenomena associated with the natural transport of water and charge in the subglacial drainage system. Streaming potentials are generated by water flow through subglacial sediment, and these potentials are closely associated with the subglaclal water pressure field. To explore these effects, we have monitored induced and natural electrical responses in the deforming material beneath Trapridge Glacier, Yukon, Canada. Several arrays of electrodes were placed at the ice-bed interface, and data were recorded over a period of several years. Data from these experiments indicate that natural potentials can be used to monitor water pressure gradients and that the bulk resistivity of the glacier bed can be altered by changing the hydraulic regime. We present evidence that temporal variations in streaming potentials can indicate fluctuations in subglacial water flow rate and that spatial variations can be related to variations in bed elevation, water pressure, and hydraulic connectivity. (Au)

F, B
Boreholes; Chemical properties; Drainage; Electrical properties; Geology; Geomorphology; Glacial melt waters; Hydrology; Measurement; Sediment transport; Thickness; Topography

G0811
Trapridge Glacier, Yukon


Evidence for temporally varying "sticky spots" at the base of Trapridge Glacier, Yukon Territory, Canada   /   Fischer, U.H.   Clarke, G.K.C.   Blatter, H.
(Journal of glaciology, v. 45, no.150, 1999, p. 352-360, ill.)
References.
ASTIS record 47439.
Languages: English
Libraries: ACU

During the 1992 summer field season we installed arrays of "plough-meters" and water-pressure transducers beneath Trapridge Glacier, Yukon Territory, Canada, to study hydromechanical coupling at the ice-bed interface. Diurnal signals recorded with two of these ploughmeters appear to correlate with fluctuations in subglacial water pressure. These diurnal variations can be explained by changes in basal resistance to sliding as mechanical conditions at the bed vary temporally in response to changes in the subglacial hydrological system. We propose that a lubricating water film, associated with high water pressures, promotes glacier sliding, whereas low pressures cause increased basal drag resulting in "sticky" areas. Using a theoretical model, we analyze the sliding motion of glacier ice over a f1at surface having variable basal drag and show that a consistent explanation can be developed. Results from our model calculations provide strong support for the existence of time-varying sticky spots which are associated with fluctuations in subglacial water pressure. (Au)

F
Diurnal variations; Drainage; Flow; Friction; Glacial melt waters; Glaciers; Glaciology; Instruments; Mathematical models; Measurement; Stress

G0811
Trapridge Glacier, Yukon


Surface and bed topography of Trapridge Glacier, Yukon Territory, Canada : digital elevation models and derived hydraulic geometry   /   Flowers, G.E.   Clarke, G.K.C.
(Journal of glaciology, v. 45, no.149, 1999, p. 165-174, ill.)
References.
ASTIS record 47438.
Languages: English
Libraries: ACU

Measurements of ice thickness and surface elevation are prerequisite to many glaciological investigations. A variety of techniques has been developed for interpretation of these data, including means of constructing regularly gridded digital elevation models (DEMs) for use in numerical studies. Here we present a simple yet statistically sound method for processing ice-penetrating radar data and describe a technique for interpolating these data onto a regular grid. DEMs generated for Trapridge Glacier, Yukon Territory, Canada, are used to derive geometric quantities that give preliminary insights into the underlying basin-scale hydrological system. This simple geometric analysis suggests that at low water pressures a dendritic drainage network exists that evolves into a uniaxial morphology as water pressure approaches flotation. These predictions are compared to hydraulic connection probabilities based on borehole drilling. (Au)

F
Boreholes; Drainage; Glacial melt waters; Glaciers; Glaciology; Instruments; Mathematical models; Radar; Thickness; Topography

G0811
Trapridge Glacier, Yukon


Stress and velocity fields in glaciers : part II. Sliding and basal stress distribution   /   Blatter, H.   Clarke, G.K.C.   Colinge, J.
(Journal of glaciology, v. 44, no.148, 1998, p. 457-466, ill.)
References.
ASTIS record 47437.
Languages: English
Libraries: ACU

Numerical methods are used to examine the interaction between the spatial distribution of the basal shear traction and the corresponding basal velocity for an inclined slab geometry. In our improved treatment, we reject the common assumption that basal velocity is a simple function of local variables in favour of a non-local treatment that includes normal deviatoric stress and takes basal velocity to be an integrated response to spatially varying influences. Computationally, one must either iterate the basal velocity with a friction parameterization that relates basal shear traction to basal velocity or, alternatively, prescribe the basal shear traction that results from bed decoupling and substrate deformation. The average of basal shear traction over the entire bed of the ice mass is invariant under changes in sliding distribution and thus constitutes a useful reference; any local relative reduction of traction leads to basal movement, either sliding over the bed or moving with a deforming subglacial layer. The local stress reduction is accompanied by a concentration of traction up- and down-glacier of the moving base. Growth, decay and possible migration of basal stress concentrations may be closely related to short-lived sliding events and to surges. (Au)

F
Flow; Glacier surges; Glacier variations; Glaciers; Mathematical models; Stress; Velocity

G0811
Trapridge Glacier, Yukon


Stick-slip sliding behaviour at the base of a glacier   /   Fischer, U.H.   Clarke, G.K.C.
(Papers from the International Symposium on Changing Glaciers, held at Fjærland, Norway, 24-27 June 1996 / Edited by I.M. Whillans. Annals of glaciology, v. 24, 1997, p. 390-396, ill.)
References.
ASTIS record 70003.
Languages: English
Libraries: ACU

Measurement of basal sliding is an important component in studying the mechanical and hydrological coupling between a glacier and its bed. During the 1992 summer field season we used a "drag spool" to measure sliding at the ice/bed interface of Trapridge Glacier, a small surge-type glacier in the St Elias Mountains, Yukon Territory, Canada. Measured diurnal variations in sliding appear to be correlated to subglacial water pressure fluctuations. In contrast to other observations where peak subglacial water pressure and glacier motion appear to coincide, our data imply that maximum sliding rates coincide with rises in water pressure. If the growth of water-filled cavities at the glacier bed is associated with these pressure increases, then our observations may correspond to numerical results by Iken (1981) which indicate that the largest sliding velocity occurs during cavity growth and not when the steady-state size of cavitation is attained. However, our data suggest the idea that a localized stick-slip relaxation process is at work. As the water pressure rises, a local strain build-up in the ice is released, resulting in a momentary increase in sliding rate; once the finite relaxation has occurred, further rises in water pressure do not produce additional enhancement of basal sliding, and the stick slip cycle begins again by accumulation of elastic strain. We have developed a theoretical model for the sliding motion of ice over a surface having a basal drag that varies temporally in response to changes in subglacial water pressure. Our model results support the proposed stick-slip sliding process at the glacier base, whereby accumulated elastic strain in the ice is released as the rising water pressure decouples the ice from the bed. (Au)

F, B
Boreholes; Deformation; Diurnal variations; Drainage; Drilling; Elasticity; Flow; Friction; Glacial deposits; Glacial melt waters; Glacier surges; Glaciers; Groundwater; Hydrology; Ice; Instruments; Interstitial water; Mathematical models; Strain; Velocity

G0811
Trapridge Glacier, Yukon


Clast collision frequency as an indicator of glacier sliding rate   /   Fischer, U.H.   Clarke, G.K.C.
(Journal of glaciology, v. 43, no.145, 1997, p. 460-466, ill.)
References.
ASTIS record 53263.
Languages: English
Libraries: ACU

The mechanical interaction between a glacier and subglacial sediment can be observed using an instrumented rod that we refer to as the UBC ploughmeter. For clast-rich sediments, the rate of collision between clasts and a rod dragged through these sediments should be related to the glacier sliding rate. By assuming that proglacial measurements of sediment granulometry represent the subglacial granulometry of Trapridge Glacier, Yukon Territory, Canada, we have used ploughmeter results to obtain an estimated sliding rate of ~45 mm/d, in good agreement with known rates. In addition, for a subglacial material treated as a solid-liquid dispersion having a linear viscous rheology, the force of collision experienced by the rod should be proportional to the effective sediment viscosity. Our estimate of ~2.0 x 10**10 Pa·s agrees well with previously derived values. (Au)

F, B
Creep; Deformation; Elasticity; Flow; Friction; Glacial deposits; Glaciers; Glaciology; Instruments; Mathematical models; Measurement; Mechanical properties; Sediments (Geology); Size; Spatial distribution; Strain; Stress; Temporal variations; Velocity; Viscosity

G0811
Trapridge Glacier, Yukon


Inversion of borehole-response test data for estimation of subglacial hydraulic properties   /   Stone, D.B.   Clarke, G.K.C.   Ellis, R.G.
(Journal of glaciology, v. 43, no.143, 1997, p. 103-113, ill.)
References.
ASTIS record 53262.
Languages: English
Libraries: ACU

Response tests are widely used in ground-water studies to assess the hydraulic properties of sub-surface water-flow systems. The simplicity of such tests also makes them attractive for investigation of subglacial hydraulic conditions. This paper describes a systematic, quantitative approach to the analysis of borehole-response test data. The approach uses the theoretical model of Stone and Clarke (1993), which describes water motion in a coupled borehole-subglacial flow system; this framework provides the basis for an inversion scheme that is focused on quantifying physical properties of the basal-flow system, as it is characterized in the theoretical model. The inversion procedure was applied to response-test data from Trapridge Glacier, Yukon Territory, Canada. Results of the inversions suggest that the subglacial drainage network can be described as a confined layer comprising coarse-sand- to fine-gravel-sized sediments, having a thickness of 0.1-0.3 m, and a hydraulic conductivity of about 5 x 10**-4m/s. Based on the water-drainage rates from boreholes, as they connect with the subglacial water-flow system, specific storage of the sediment layer was estimated to be approximately 1 x 10**-4/m. Further consideration of subglacial water-flow conditions suggests that connection-drainage test results may tend to underestimate specific storage of the overall glacier substrate. (Au)

F, B
Boreholes; Compressive properties; Density; Diurnal variations; Drainage; Flow; Friction; Glacial deposits; Glacial melt waters; Glaciers; Groundwater; Hydrology; Instruments; Mathematical models; Movement; Physical properties; Sediments (Geology); Temporal variations; Thickness; Viscosity

G0811
Trapridge Glacier, Yukon


In situ measurements of basal water quality and pressure as an indicator of the character of subglacial drainage systems   /   Stone, D.B.   Clarke, G.K.C.
(Hydrological processes, v. 10, no. 4, Apr. 1996, p. 615-629, ill.)
References.
ASTIS record 69996.
Languages: English
Web: doi:10.1002/(SICI)1099-1085(199604)10:4<615::AID-HYP395>3.0.CO;2-M
Libraries: ACU

Continuous subglacial measurements of turbidity and electrical conductivity - two indicators of basal water quality - can be used to help characterize subglacial drainage systems. These indicators of water quality yield information that complements that provided by water pressure measurements. Quantitative attributes of subglacial drainage systems, such as water velocity and subglacial residence time, as well as qualitative behaviour - for example, spatial and temporal variations in system morphology - can be deduced using water quality measurements. Interpretation is complicated by the many potential influences on turbidity and electrical conductivity, but when these complications are appreciated a richer interpretation results. To demonstrate the utility of basal water quality measurements, observations from Trapridge Glacier, Yukon Territory, Canada were examined. The data reveal complex behaviour of the drainage system, but constraints imposed by basal water quality measurements help to clarify the nature of the subglacial flow system. The measurement and interpretation methods described and demonstrated are applicable to other glaciers. As such, they should prove useful for characterizing different subglacial drainage configurations and behaviours, thereby improving our general understanding of the hydrology and dynamics of wet-based glaciers. (Au)

F
Boreholes; Diurnal variations; Drainage; Effects monitoring; Electrical properties; Flow; Glacial melt waters; Glacier ice; Glacier surges; Glaciers; Glaciology; Instruments; Mathematical models; Measurement; Melting; Physical properties; Sediment transport; Sediments (Geology); Size; Spatial distribution; Suspended solids; Temporal variations; Testing; Thermal regimes; Velocity

G0811
Trapridge Glacier, Yukon


Lumped-element analysis of subglacial hydraulic circuits   /   Clarke, G.K.C.
(Journal of geophysical research, v.101, no. B 8, Aug. 10, 1996, p.17,547-17,559, ill.)
References.
ASTIS record 69984.
Languages: English
Web: doi:10.1029/96JB01508
Libraries: ACU

Observations of the subglacial hydrological system reveal a richness of responses that axe thought to reflect variations in the water supply, morphology, and connectivity of the system. To contribute insight into the physical controls that result in qualitative variations in system response, a lumped-element formalism is developed and used to simulate the behavior of simple hydraulic circuits. The circuit elements for an idealized subglacial water system differ from those used to analyze conventional hydraulic flows, but the motivation is similar: lumped systems are governed by ordinary differential equations, whereas continuous systems are governed by partial differential equations. The accompanying examples illustrate the capture property of Rothlisberger channels, the concept of morphological switching, the role of water storage geometry in contributing to system nonlinearity, and the effects of seasonal variations in storage capacity and hydraulic resistance. (Au)

F
Crevasses; Drainage; Flow; Glacial melt waters; Glacier surges; Glaciers; Glaciology; Hydrology; Mathematical models; Physical properties; Seasonal variations; Temporal variations; Velocity

G0811
Trapridge Glacier, Yukon


Lumped-element model for subglacial transport of solute and suspended sediment   /   Clarke, G.K.C.
(Proceedings of the International Symposium on Glacial Erosion and Sedimentation, held at Reykjavik, Iceland, 20-25 August 1995 / Edited by D.N. Collins. Annals of glaciology, v. 22, 1996, p. 152-159, ill.)
References.
ASTIS record 53303.
Languages: English
Libraries: ACU

Present understanding of the subglacial water system and its role in transporting solute and sediment is largely based on subglacial observations of water pressure, turbidity and electrical conductivity and on portal measurements. Such data reveal a wealth of intriguing phenomena, but convincing interpretations can be elusive. Although a proper mathematical description of the subglacial water system would unquestionably lead to a coupled system of non-linear partial differential equations, it is not fruitful to introduce this level of complexity until the important physical processes have been identified and quantified. Lumped-element models offer an efficient approach to examining the complex but dimly perceived physics of the subglacial water system. Water volume, hydraulic head, discharge and low resistance have the respective electrical analogues of charge, voltage, current and ohmic resistance. Thus, subglacial hydraulic circuits can be approximated by electrical circuits. Mathematically, this circuit description commonly leads to a coupled system of algebraic and differential equations which can he solved numerically. It is straightforward to enrich this representation by adding sources and sinks of solute and sediment. To demonstrate the method, model results are compared to records of subglacial pressure, electrical conductivity and turbidity measured beneath Trapridge Glacier, Yukon Territory, Canada. (Au)

F, B, A
Chemistry; Electrical properties; Erosion; Glacial melt waters; Glacial transport; Glaciers; Hydrology; Mathematical models; Physics; River discharges; Runoff; Sediment transport; Sedimentation; Sediments (Geology); Size; Stream flow; Suspended solids

G0811
Trapridge Glacier, Yukon


Geologic and topographic controls on fast flow in the Laurentide and Cordilleran Ice Sheets   /   Marshall, S.J.   Clarke, G.K.C.   Dyke, A.S.   Fisher, D.A.
(Journal of geophysical research, v.101, no. B 8, Aug. 10, 1996, p.17,827-17,839, ill., maps)
References.
ASTIS record 52540.
Languages: English
Web: doi:10.1029/96JB01180
Libraries: ACU

Ice streams are fast flowing arteries which play a vital role in the dynamics and mass balance of present-day ice sheets. Although not fully understood, fast flow dynamics are intimately coupled with geologic, topographic, thermal, and hydrologic conditions of the underlying bed. These are difficult observables beneath contemporary ice sheets, hindering elucidation of the processes which govern ice stream behavior. For past ice sheets the problem is antithetic. Geologic evidence of former ice streams exists, but spatial and temporal histories are uncertain; however, detailed knowledge of bed geology and topography is available in many places. We take advantage of this information to compile terrain characteristics relevant to fast flow dynamics in the Laurentide and Cordilleran Ice Sheets. Using seed points where fast flowing Wisconsinan ice has been geologically inferred, discriminant analysis of a suite of North American geologic and topographic properties yields a concise measure of ice-bed coupling strength. Our analysis suggests that the interior plains and continental shelf regions of North America have low basal coupling relative to areas of variable relief or exposed bedrock in the Cordillera and on the Canadian Shield. We conclude that the interior plains and continental shelves are both topographically and geologically predisposed to large-scale basal flows (i.e., ice streams or surge lobes). This result holds independent of whether the mechanism of fast flow is sediment deformation or decoupled sliding over the bed. (Au)

F, B, A
Continental shelves; Deformation; Flow; Geology; Geomorphology; Glacial deposits; Glacial epoch; Glacial landforms; Glacier surges; Glacier variations; Hydrology; Ice sheets; Laurentide Ice Sheet; Mass balance; Mathematical models; Mechanical properties; Melting; Physical geography; Sediments (Geology); Spatial distribution; Temporal variations; Thermal regimes; Thickness; Topography; Velocity

G08, G081, G10
Canada; Canadian Arctic; Greenland; United States


Black-box modeling of the subglacial water system   /   Murray, T.   Clarke, G.K.C.
(Journal of geophysical research, v.100, no. B 7, June 10, 1995, p.10,231-10,245, ill., maps)
References.
ASTIS record 70005.
Languages: English
Web: doi:10.1029/95JB00671
Libraries: ACU

Measurements of water pressure beneath Trapridge Glacier, Yukon Territory, Canada, yield the following generalizations about subglacial conditions in the studied region: (1) Even over short distances the subglacial water system is highly heterogeneous. (2) The subglacial water system consists of at least two distinct components which we refer to as the "connected" and "unconnected" water systems. (3) Regions of the glacier bed can switch back and forth from being part of the connected or part of the unconnected water system. (4) Large spatial pressure gradients can exist within the unconnected water system, and between the connected and unconnected systems. (5) Rapid pressure variations can occur in the unconnected water system. (6) Pressure variations in the unconnected water system do not match those in the connected system and can, in fact, be strongly anticorrelated with pressure variations in the connected system. If the water pressure variations in the connected system are viewed as a forcing and those in the unconnected system as a response to this forcing, the input-output relation between forcing and response can be efficiently represented as a low-order nonlinear ordinary differential equation. The response of the unconnected system to forcing from the connected system is governed by time constants having approximate magnitudes of ~1.7 hours and ~7.4 hours that we believe are associated with process rates for substrate compression and pore water diffusion, respectively. (Au)

F
Boreholes; Diurnal variations; Drainage; Electrical properties; Flow; Glacial deposits; Glacial melt waters; Glacier surges; Glaciers; Groundwater; Hydrology; Ice; Instruments; Mathematical models; Measurement; Mechanical properties; Neutral stress; Physical properties; Seasonal variations; Water level

G0811
Trapridge Glacier, Yukon


Hydraulic properties of subglacial sediment determined from the mechanical response of water-filled boreholes   /   Waddington, B.S.   Clarke, G.K.C.
(Journal of glaciology, v. 41, no.137, 1995, p. 112-124, ill.)
References.
ASTIS record 69976.
Languages: English
Libraries: ACU

Freezing of water-filled boreholes drives water into the subglacial bed and the associated pressure effects yield information about subglacial hydraulic properties. A numerical model describing the mechanical response of an unconnected borehole and the bed beneath it to this freezing forcing was developed, using a nonlinear transient visco-elastic ice-flow law and an approximate model of top-down freezing. The resulting system of equations was solved using the method of lines. Results agreed well with analytic solutions, when parameters were correctly chosen. Forward modelling of pressure records from three 1992 boreholes and three from other years indicated that the till underlying Trapridge Glacier has a hydraulic conductivity of 1.35-7.0 × 10**-9 m/s. The model was also used to investigate the response of a borehole to sudden pressure changes. The response is very fast compared to pressure-sensor sampling rates; thus, the true basal signal is essentially unaffected by the presence of the borehole, except during the initial freeze-in. (Au)

F
Boreholes; Deformation; Drilling; Equipment and supplies; Flow; Glacial deposits; Glacial melt waters; Glacier ice; Glacier surges; Glaciers; Glaciology; Instruments; Mathematical models; Measurement; Mechanical properties; Melting; Physical properties; Strain; Temporal variations; Testing; Velocity

G0811
Trapridge Glacier, Yukon


Direct measurement of sliding at the glacier bed   /   Blake, E.W.   Fischer, U.H.   Clarke, G.K.C.
(Journal of glaciology, v. 40, no.136, 1994, p. 595-599, ill.)
References.
ASTIS record 69991.
Languages: English
Libraries: ACU

Sliding at the base of Trapridge Glacier, Yukon Territory, Canada, was measured using a “drag spool”. We describe this simple and inexpensive instrument as well as its installation and operation. From 1990 to 1992 seven sites were instrumented with drag spools. At six of the sites basal sliding, during the period of observation, accounted for 50-70% of the total flow observed at the glacier surface. The contribution from ice creep is known to be small, so most of the remaining surface motion must be attributed to subglacial sediment deformation. For the seventh site the observed sliding rate was 90% of the total flow, an indication that the sliding contribution varies spatially across the bed. Diurnal variations in the response of one of our instruments appear to be correlated to subglacial water-pressure fluctuations and are interpreted in terms of changes in sliding velocity rather than the opening and closing of basal cavities. (Au)

F
Boreholes; Creep; Deformation; Diurnal variations; Equipment and supplies; Flow; Glacial melt waters; Glacier ice; Glaciers; Instruments; Measurement; Mechanical properties; Models; Sediments (Geology); Temporal variations; Testing; Velocity

G0811
Trapridge Glacier, Yukon


Miniature high-power impulse transmitter for radio-echo sounding   /   Narod, B.B.   Clarke, G.K.C.
(Journal of glaciology, v. 40, no.134, 1994, p. 190-194, ill.)
References.
ASTIS record 69987.
Languages: English
Libraries: ACU

We have developed a miniature high-power impulse transmitter for radio-echo sounding of glaciers. It features two synchronous second break-down pulse generators operating in a differential configuration. Specifications include bipolar 550 V pulses having rise times less than 2 ns, 512 Hz repetition rate, 180 mA at 10-14 V d.c. operating power, 5 mA standby current and maximum dimension of 12 cm. Because of its small size and low power consumption, the transmitter is suitable for back-portable systems and for towed arrays. The transmitter first saw service in 1990 on Trapridge Glacier, Yukon Territory. Subsequent copies have been used on Agassiz Ice Cap, Northwest Territories, Bering Glacier, Alaska and elsewhere. To date, the maximum ice thickness measured using this transmitter is 825 m, on temperate Bering Glacier. (Au)

F
Antennae; Design and construction; Glaciers; Instruments; Measurement; Physical properties; Radar; Specifications; Testing; Thickness

G0811, G0813, G06
Agassiz Ice Cap, Nunavut; Bering Glacier, Alaska; Trapridge Glacier, Yukon


Ploughing of subglacial sediment   /   Fischer, U.H.   Clarke, G.K.C.
(Journal of glaciology, v. 40, no.134, 1994, p. 97-106, ill.)
Appendix: Forces on an elongated body in strokes flow.
References.
ASTIS record 69983.
Languages: English
Libraries: ACU

Mechanical conditions at the base of Trapridge Glacier, Yukon Territory, were investigated using a “ploughmeter”. We describe the physical characteristics and the theory of this new instrument as well as its operation. Observational results reveal variations in ploughmeter response that might be attributed to spatial variability in subglacial processes or spatial variation in sediment granulometry. Quantitative analysis of the interaction of the ploughmeter with the basal layer yields estimates of rheological parameters. If the sediment is assumed to behave as a Newtonian viscous fluid, the estimated effective viscosity is 3.0 × l0**9 - 3.1 × 10**10 Pa s; if it is assumed to behave as an ideal plastic solid, the estimated yield strength is 48-57 kPa. In both cases, the estimated shear resistance of subglacial material is comparable to but somewhat less than that required to balance fully the applied basal shear stress. (Au)

F
Boreholes; Boundary layers; Deformation; Design and construction; Drainage; Flow; Glacial deposits; Glacial melt waters; Glacier ice; Glaciers; Glaciology; Instruments; Mathematical models; Measurement; Mechanical properties; Melting; Physical properties; Sediments (Geology); Spatial distribution; Strain; Temperature; Temporal variations; Testing; Velocity; Viscosity

G0811
Trapridge Glacier, Yukon


Ice age cycles : questions and answers under the glacier = Les cycles glaciaires : les questions et réponses trouvés sous le glacier   /   Marshall, S.J.   Clarke, G.K.C.
In: Fourth National Student Conference on Northern Studies : Conference programme and abstracts, Government Conference Centre, Ottawa, November 26-27, 1994 = Quatrième conférence nationale des étudiants en études nordiques : Calendrier des événements et sommaires, Centre de Conférence du Gouvernement, Ottawa, du 26 au 27 novembre 1994. - Ottawa : ACUNS, 1994, p. [72]
Abstract only.
ASTIS record 36664.
Languages: English and French
Libraries: ACU

The traditional view of Ice Age cycles invokes stately accumulation of ice masses in response to climatic forcing. Ice sheets creep steadily southward from northern highland source regions, followed by rapid meltback and retreat at glacial terminations. Mounting geomorphic, palynologic, paleoceanographic, and ice core evidence suggests that ice sheets were much more dynamic, with rapid and episodic fluctuations dictated by internal and subglacial flow instabilities. Fast glacier flow results from decoupled sliding over the ice sheet bed or from failure and deformation of subglacial sediments. Each flow mechanism is driven at the bed and is governed by geology, topography, and by thermal and hydrologic conditions beneath the ice. Improved understanding of ice sheet evolution requires better understanding of these processes and controls. We are undertaking a three-pronged attack to this end: (1) Field study of subglacial processes beneath a surge-type glacier in the St. Elias Mountains, Yukon Territory. (2) Geological reconstructions of basal environment and processes formerly active beneath the Laurentide Ice Sheet which covered Canada. The Laurentide bed is accessible and preserves many hints to hydrologic and ice-dynamic histories. (3) Numerical modelling of the Laurentide Ice Sheet to test subglacial process models. We have developed a comprehensive model which includes ice sheet dynamics, ice sheet and ground thermodynamics, and detailed bed geology and topography. The model is constrained by reconstructions and observational insights. This integrated approach promises to improve our understanding of basal process physics and past behaviour of the Laurentide Ice Sheet. (Au)

A, F
Deglaciation; Flow; Glacial epoch; Glacier surges; Glacier variations; Glaciology; Ice sheets; Laurentide Ice Sheet; Mathematical models; Thermodynamics

G0811
St. Elias Mountains, Alaska/British Columbia/Yukon


Subglacial measurement of turbidity and electrical conductivity   /   Stone, D.B.   Clarke, G.K.C.   Blake, E.W.
(Journal of glaciology, v. 39, no.132, 1993, p. 415-420, ill.)
References.
ASTIS record 69982.
Languages: English
Libraries: ACU

Direct measurements of the properties of subglacial water are necessary for understanding water flow beneath glaciers. In this paper we describe the construction, calibration and field usage of two instruments - one that measures turbidity and the other that measures electrical conductivity of subglacial water. The sensors are inexpensive and reliable. To demonstrate the potential usefulness of these devices, we present samples of data obtained from beneath Trapridge Glacier, Yukon Territory, Canada. (Au)

F
Boreholes; Design and construction; Drainage; Electrical properties; Flow; Glacial melt waters; Glacier ice; Glaciers; Glaciology; Instruments; Measurement; Melting; Suspended solids; Temperature; Temporal variations; Testing; Velocity

G0811
Trapridge Glacier, Yukon


Estimation of subglacial hydraulic properties from induced changes in basal water pressure : a theoretical framework for borehole-response tests   /   Stone, D.B.   Clarke, G.K.C.
(Journal of glaciology, v. 39, no.132, 1993, p. 327-340, ill.)
References.
ASTIS record 69978.
Languages: English
Libraries: ACU

In this paper we develop a theoretical model describing water motion in a coupled borehole-subglacial flow system. The theory applies to basal drainage systems having multiple and extensive interconnected flow paths. Within this domain it encompasses a broad range of flow regimes, from laminar Darcian flow in a thick permeable unit to turbulent sheet flow in a very thin layer. Important terms in the model are highlighted by recasting the problem in dimensionless form. The non-dimensional formulation indicates that there are four free parameters in the coupled system. These parameters characterize skin friction in the borehole, and diffusion, transmissivity and turbulent transport in the subglacial flow layer. Dimensionless results show that, under most circumstances, the effects of skin friction in the borehole are negligible. Diffusion, transmissivity and especially turbulent transport in the basal layer are found to influence subglacial water flow strongly. We use our model to predict fluctuations of borehole-water levels that result from different types of disturbances. We show how this framework can be used to estimate subglacial hydraulic properties by comparing model results with data collected during field experiments on Trapridge Glacier, Yukon Territory, Canada, in 1989 and 1990. (Au)

F
Aquifers; Boreholes; Boundary layers; Drainage; Flow; Friction; Glacial melt waters; Glacier ice; Glacier surges; Glaciers; Glaciology; Mathematical models; Measurement; Mechanical properties; Melting; Physical properties; Stress; Temporal variations; Testing; Velocity

G0811
Trapridge Glacier, Yukon


Tools for examining subglacial bed deformation   /   Blake, E.   Clarke, G.K.C.   Gérin, M.C.
(Journal of glaciology, v. 38, no.130, 1992, p. 388-396, ill.)
References.
ASTIS record 69975.
Languages: English
Libraries: ACU

Deformation beneath soft-bedded glaciers may be a physical mechanism that contributes to flow instabilities such as surging. If the role of bed deformation is to be understood, a rheological description is required, but the development of a rheology is hampered by a lack of in situ stress and strain measurements. In this paper, we describe four techniques for measuring subglacial strain. Three of these give continuous strain measurements, a capability that permits calculation of instantaneous strain rates and allows comparison of strain data with other time series. To demonstrate the practicability of the techniques, sample results from three summers of experimentation beneath Trapridge Glacier, Yukon Territory, are presented. The data show that subglacial strain rate can vary in amplitude and polarity on an hourly time-scale, and that the instantaneous strain rate can exceed the mean strain rate by an order of magnitude. Observed negative strain rates suggest extrusive flow within basal sediments. (Au)

F, B
Boreholes; Deformation; Drilling; Equipment and supplies; Flow; Glacier ice; Glacier surges; Glaciers; Glaciology; Instruments; Mathematical models; Measurement; Sediments (Geology); Strain; Temporal variations; Velocity

G0811
Trapridge Glacier, Yukon


Interpretation of borehole-inclinometer data : a general theory applied to a new instrument   /   Blake, E.W.   Clarke, G.K.C.
(Journal of glaciology, v. 38, no.128, 1992, p. 113-124, ill.)
Appendices.
References.
ASTIS record 69972.
Languages: English
Libraries: ACU

Borehole inclinometers are standard equipment for field glaciologists and are commonly used for investigating the flow law of ice and for measuring the spatial position of englacial and sub-surface sensors. The recent development, at the University of British Columbia (UBC), of a prototype inclinometer that employs a three-component fluxgate magnetometer to obtain a compass bearing has stimulated our interest in borehole inclinometry. Following a review of various approaches to glacier inclinometry, we present a unified theory of data interpretation that can be applied to all inclinometers, discuss the application of the theory to the UBC inclinometer, and discuss the sensitivity of the theory to error in the data. (Au)

F, B
Boreholes; Design and construction; Drilling; Equipment and supplies; Flow; Geomagnetism; Glaciers; Glaciology; Instruments; Mapping; Mathematical models; Measurement; Spatial distribution; Temporal variations; Velocity

G0811
Trapridge Glacier, Yukon


Length, width and slope influences on glacier surging   /   Clarke, G.K.C.
(Journal of glaciology, v. 37, no.126, 1991, p. 236-246, ill.)
References.
ASTIS record 69970.
Languages: English
Libraries: ACU

Statistical analysis of 1754 normal and surge-type glaciers of the Yukon Territory, Canada, reveals that the two glacier types have significantly different average geometries. Surge-type glaciers tend to be longer, wider and to have lower overall slope than normal glaciers. Because there are strong intercorrelations involving length, width and slope, it is not immediately clear which relationships are fundamental and which are secondary. Multiple correlation analysis allows these confusions to be resolved and reveals that the correlation between length and surge tendency is the fundamental one. The direct correlation between surge tendency and width and the inverse correlation between surge tendency and slope are entirely a result of the length-width and length-slope correlations. This conclusion may have implications for the glacier-surge mechanism because one prediction of the Kamb theory of surging is that small slopes (as opposed to great lengths) favour surging. Fowler's theory of surging predicts that glaciers for which the product theta w² (where theta is slope and w is width) is small are more likely to be surge-type than those for which the product is large, but analysis of the correlation between this parameter and surge tendency lends no support to this claim. (Au)

F
Glacier surges; Glaciers; Glaciology; Mathematical models; Measurement; Size; Slopes

G0811
Yukon


Geometric and thermal evolution of a surge-type glacier in its quiescent state : Trapridge Glacier, Yukon Territory, Canada, 1969-89   /   Clarke, G.K.C.   Blake, E.W.
(Journal of glaciology, v. 37, no.125, 1991, p. 158-169, ill., maps)
References.
ASTIS record 32327.
Languages: English
Libraries: ACU

Trapridge Glacier, Yukon Territory, Canada is a sub-polar surge-type glacier. It last surged in the 1940s and is now in the late stages of quiescence. Since 1969, when the glacier was first surveyed, a large wave-like bulge has formed near the glacier terminus. Surveys from 1969-89 show the profile evolution that has accompanied the formation and downflow propagation of this feature. Ice-temperature measurements taken in 1980-81 established that the bulge was forming at the boundary between thick warm-based ice lying up-glacier from the bulge, and thin cold-based ice lying down-glacier from it. The bulge is propagating at roughly 30 m/a and thick ice has now completely overridden the region once covered by thin cold-based ice that were instrumented in 1980-81. In 1987, and again in 1988, the geographical positions of the 1980 measurement sites were then re-drilled and instrumented with new thermistor cables. Comparison of the 1980-81 data with that from 1987-88 shows that this region of the glacier has undergone a dramatic change in geometry and thermal regime. Water penetration into surface crevasses has warmed the 15-m ice temperature by roughly 2° C. The zone of transition from warm- to cold-based ice is migrating down-glacier but at a slower rate than that of the bulge feature. The transition from warm-based to cold-based ice appears to cause a discontinuity in the flow that resembles a transition for flow over a sliding boundary to flow over an adhering boundary. The discontinuity in the flow field is associated with anomalies in the temperature field and appears to be the source region for an englacial structure formed from subglacial sediment. This structure was not present in 1980-81 and is thought to have the geometry of a thrust fault of recumbent fold. (Au)

F
Crevasses; Flow; Glacier surges; Glaciers; Thermal regimes

G0811
Trapridge Glacier, Yukon


Subglacial water and sediment samplers   /   Blake, E.W.   Clarke, G.K.C.
(Journal of glaciology, v. 37, no.125, 1991, p. 188-190, ill.)
References.
ASTIS record 32326.
Languages: English
Libraries: ACU

The current focus of glaciological research on basal processes and hydrology makes the acquisition of samples from the subglacial environment a vital enterprise. In this letter, two devices are described for obtaining samples of basal water and sediment within the confines of a narrow borehole. The samplers have been operated at depths ranging from 70 to 300m. They are lightweight and require only a single operator. (Au)

F
Cores; Coring; Equipment and supplies; Glaciers; Glaciology

G0811
Trapridge Glacier, Yukon


Temporal changes in subglacial acoustic properties   /   Clarke, G.K.C.   Blake, E.W.
(Eos (Washington, D.C.), v. 71, no. 43, Oct. 23, 1990, p.1314-1315)
Not seen by ASTIS. Citation from NSTP.
ASTIS record 31009.
Languages: English
Libraries: ACU

Seismic studies of west Antarctic ice stream B reveal that the S-wave velocity in underlying sediments is remarkably low. Drill holes to the base of the ice stream confirm that the subglacial material is deforming water-saturated till. This association of deformation with low S-wave velocity is expected because both are a consequence of low rigidity µ. Following this reasoning, if subglacial sediment deforms at an irregular rate then this may imply that sediment rigidity is temporally variable and that temporal variations in acoustic properties such as the P- and S-wave velocities might occur. In summer 1990 we attempted to observe temporal changes in the acoustic properties of sediment beneath Trapridge Glacier, Yukon Territory, Canada. The glacier is surge-type and is known to have spatially and temporally variable subglacial deformation rates. Our experiment involved placing a controlled seismic source near the bed of Trapridge Glacier and observing seismic arrivals using a subglacial array of five geophones. Suites of seismograms were collected at 20-minute intervals for three weeks. Subglacial water pressure and basal sliding rate near the array were continuously recorded throughout the experiment. We report the results of these seismic measurements. (Au)

F
Acoustic properties; Deformation; Glacial deposits; Glacial melt waters; Glacier surges; Glaciers; Seismic sounding

G0811
Trapridge Glacier, Yukon


Lacustrine sedimentary record of ice-dammed neoglacial Lake Alsek   /   Schmok, J.P.   Clarke, G.K.C.
(Canadian journal of earth sciences, v. 26, no. 10, Oct. 1989, p.2092-2105, ill., 1 map)
References.
Not seen by ASTIS. Citation from NSTP.
ASTIS record 30084.
Languages: English
Web: doi:10.1139/e89-176
Libraries: ACU

Neoglacial Lake Alsek is an ice-dammed lake in the southwest Yukon that forms when Lowell Glacier rapidly advances from a side valley to block the Alsek River. A sedimentary record of past fillings and catastrophic drainages is preserved in small lakes lying within the Lake Alsek basin. Sediment cores from some of these small lakes were retrieved and studied. The cores were subjected to facies analysis involving description, classification, and interpretation of depositional processes, leading to assessment of depositional environment. Despite a relatively sparse set of sedimentary data, five distinctive deposits and associated environments can be recognized: (1) matrix supported diamicton interpreted as a deposit of iceberg-rafted sediment, (2) sand and coarse silt interpreted as tractive current deposits, (3) massive silt and clay interpreted as rapidly deposited, lake margin derived sediment, (4) laminated silt and clay interpreted as glaciolacustrine deposits, and (5) carbonaceous muds interpreted as eutrophic pond deposits. Facies sequence analysis reveals that the sedimentary sequences are non-randomly ordered, but cyclicity of the deposits was not found. Erosional unconformities reflecting gaps in the sediment record and difficulties with basin wide stratigraphic correlations both hamper further definition of the Lake Alsek filling and draining chronology. These problems could be overcome in future studies if either greater exposures could be studied or sufficient chronostratigraphic information could be obtained. (Au)

B, F, A
Bottom sediments; Cores; Drainage; Glacial melt waters; Glacier lake outbursts; Glaciers; Physical geography; Sedimentation

G0811
Alsek River region, Alaska/British Columbia/Yukon; Kluane National Park and Reserve, Yukon


Design and operation of a portable, digital impulse radar   /   Jones, F.H.M.   Narod, B.B.   Clarke, G.K.C.
(Journal of glaciology, v. 35, no.119, 1989, p. 143-148)
Not seen by ASTIS. Citation from NSTP.
ASTIS record 30083.
Languages: English

We have constructed a back-portable, impulse radar instrument that weighs roughly 12 kg, can be powered by dry cells, and records and stores data digitally. The radar is controlled by an on-board, purpose-built microcomputer that ensures simple field operation, facilitates modifications, and allows unattended operation when investigating time-varying targets. The transmitting unit is triggered from the receiver via an optical link and generates an electromagnetic wavelet by discharging two high-voltage capacitors through back-to-back silicon-controlled rectifiers into a resistively loaded dipole antenna. Successful field operations carried out during the summers of 1986 and 1987 include depth profiling, as well as studies of englacial and subglacial targets, on several temperate and sub-polar glaciers. (Au)

F
Antennae; Glaciers; Measurement; Radar; Thickness

G0811
Trapridge Glacier, Yukon


In situ bed strain measurements beneath a surge-type glacier   /   Blake, E.W.   Clarke, G.K.C.
(Eos (Washington, D.C.), v. 70, no. 43, Oct. 24, 1989, p.1084)
Abstract only.
Paper presented at the American Geophysical Union 1989 Fall Meeting in San Francisco, Calif., 4-8 Dec., 1989.
Not seen by ASTIS. Citation from NSTP.
ASTIS record 30082.
Languages: English
Libraries: ACU

Trapridge Glacier is a surge-type glacier and our confirmations that it lies on an unlithified deformable bed points to the viability of a soft-bed surge mechanism. For soft-bedded glaciers, substrate deformation is likely to oppose the establishment of subglacial drainage paths. This could be the process that disables the subglacial water system during surges. Vertical strings of dual-axis tilt sensors were inserted beneath Trapridge Glacier, Yukon Territory, during the 1988 and 1989 summer field seasons. By measuring the tilt variation with time and depth we find that the glacier is underlain by -0.5 m of deforming material, presumably water-saturated till. The effective viscosity of this deforming layer varies temporally from 109 Pa's to infinity (zero strain rate) but this variation has no clear relationship to fluctuations in subglacial water pressure. (Au)

F
Formation; Glacier surges; Glaciers; Measurement; Strain

G0811
Trapridge Glacier, Yukon


Stable-isotope pattern predicted in surge-type glaciers   /   Waddington, E.D.   Clarke, G.K.C.
(Canadian journal of earth sciences, v. 25, no. 5, May 1988, p. 657-668, ill., maps)
References.
ASTIS record 69994.
Languages: English
Web: doi:10.1139/e88-063
Libraries: ACU

The distribution pattern of stable-isotope ratio delta 18O in cold glaciers, ice streams, and ice sheets has the potential to reveal past changes in flow rate, for example those associated with surges. In this study, we use a time-dependent numerical model of ice flow to establish that each surge creates a stratigraphic horizon across which delta 18O is discontinuous. Two plausible relations between glacier geometry and delta 18O in snowfall allow us to bracket the expected magnitude of this isotopic signal. These stratigraphic markers could be located by delta 18O analysis of a longitudinal series of ice cores or by detailed longitudinal sampling of exposed ice. Calculations for a model with characteristics resembling those of Steele Glacier, Yukon Territory, showed that at most three stratigraphic markers could be detected at any one time. The discontinuities in delta 18O were as large as 0.8‰. This is an order of magnitude larger than mass spectrometer precision but comparable to observed background noise at Steele Glacier. (Au)

F, E
Boreholes; Climate change; Cores; Deuterium; Flow; Glacial melt waters; Glacier ice; Glacier surges; Glaciers; Ice sheets; Isotopes; Mass balance; Mathematical models; Oxygen; Precipitation (Meteorology); Seasonal variations; Size; Snow; Temperature; Temporal variations; Thickness; Velocity

G0811, G01
Polar regions; Steele Glacier, Yukon


Geometric and thermal evolution of Trapridge Glacier   /   Clarke, G.K.C.   Blake, E.W.
Paper presented at the American Geophysical Union, Fall Meeting, San Francisco, Calif., 5-9 Dec., 1988.
Not seen by ASTIS. Citation from NSTP.
ASTIS record 29008.
Languages: English

Trapridge Glacier, Yukon, Canada is a sub-polar surge-type glacier. It last surged in the 1940s and is now in the late stages of its quiescent phase. Since 1969, when the glacier was first surveyed, a large wave-like bulge has formed near the glacier terminus. Ice temperature measurements taken in 1980-81 established that the bulge was forming at the boundary between thick warm-based ice lying upglacier from the bulge, and thin cold-based ice lying downglacier from it. The bulge is propagating at roughly 30 m/yr and thick ice has now completely overridden the thin cold-based region that we instrumented in 1980-81. In 1987-88, the 1980 geographical positions of these former measurement sites were redrilled and instrumented with thermistor cables. Comparison of the 1980-81 data with that from 1987-88 shows that the former cold-based zone has undergone a dramatic change in thermal regime and that the boundary between warm- and cold-based ice is migrating downglacier with the bulge. (Au)

F
Drainage; Flow; Glacier surges; Glaciers; Thermal regimes

G0811
St. Elias Mountains, Alaska/British Columbia/Yukon; Trapridge Glacier, Yukon


Subglacial electrical phenomena   /   Blake, E.W.   Clarke, G.K.C.
Paper presented at the American Geophysical Union, Fall Meeting, San Francisco, Calif., 5-9 Dec., 1988.
Not seen by ASTIS. Citation from NSTP.
ASTIS record 29007.
Languages: English

Measurement of subglacial electrical phenomena offers a new approach to observing changes in the subglacial water system. Using hotwater drilling we have installed arrays of electrodes at the bed of Trapridge Glacier, a surge-type glacier in Yukon. Active geoelectric sounding using these arrays yields information about water content, electrical anisotropy, and resistivity structure of the glacier bed, and how these characteristics vary. These may be attributed to geomagnetically-induced telluric currents flowing through the glacier substrate. These may be attributed to geomagnetically-induced telluric currents and to streaming potentials generated by ionic water flow through electrostatically active material, for example matrix clay in glacial till. Variations in streaming potentials can be linked with changes in the morphology and flow rate of the subglacial water system. Both active and passive measurements are sensitive to electrode position, thus borehole inclinometry is an essential prerequisite to quantitative interpretation. (Au)

F
Drainage; Flow; Glacier surges; Glaciers

G0811
St. Elias Mountains, Alaska/British Columbia/Yukon; Trapridge Glacier, Yukon


Fast glacier flow : ice streams, surging, and tidewater glaciers   /   Clarke, G.K.C.
(Journal of geophysical research, v. 92, no. B 9, Aug. 10, 1987, p.8835-8841, ill.)
References.
ASTIS record 71354.
Languages: English
Web: doi:10.1029/JB092iB09p08835
Libraries: ACU

... Ice streams and tidewater glaciers seem able to switch between slow and fast modes of flow. In the case of tidewater glaciers the switchover is externally triggered, either by ice thinning or by rising sea level, whereas for ice streams it is uncertain whether it is internally or externally triggered. Of special interest are glaciers that demonstrate intrinsically unstable flow or "surging" [Meier and Post, 1969]. Unlike normal valley glaciers that can maintain a fairly steady flow rate and adjust stably to external changes, surging glaciers experience extreme flow pulsations (Figure 3). Variegated Glacier in Alaska has become the type example of a surging glacier. Its most recent surge occurred in 1982-1983 and was closely monitored [Karnb et al., 1985; Httmphrey et al., 1986; Raymond et al., this issue]. The maximum velocity measured during the surge exceeded 23,000m/yr and was maintained for about 2 hours [Kamb et al., 1985]. Surges of Variegated Glacier are known to have occurred in 1906, some years before 1933, about 1947, 1964-1965, and in 1982-1983, suggesting an approximate periodicity of 19 years. Between surges the glacier becomes nearly stagnant. Although surge-type glaciers are uncommon (some 200 have been identified in North America), they have unique scientific importance. Their very existence suggests that different physical processes control slow and fast flow. Surging glaciers cross and recross the threshold between processes that dominate slow flow and those that dominate fast flow. By studying surging glaciers it should be possible to identify these processes and learn the causes of flow instability. For this reason, glaciologists assign the highest priority to understanding the mechanics of surging. The paper by Raymond [this issue] is the most recent review of this important subject, and the only one that incorporates recently acquired insights from the study of the Variegated Glacier surge. (Au)

F
Deformation; Flow; Glacial melt waters; Glacier surges; Glaciers; Mass balance; Mathematical models; Velocity

G06, G10, G15, G0811
Antarctic regions; Columbia Glacier, Alaska; Dusty Glacier, Yukon; Jakobshavn Isbræ, Greenland; Variegated Glacier, Alaska; White Mountain, Alaska


Subglacial till : a physical framework for its properties and processes   /   Clarke, G.K.C.
(Journal of geophysical research, v. 92, no. B 9, Aug. 10, 1987, p.9023-9036, ill.)
References.
ASTIS record 70004.
Languages: English
Web: doi:10.1029/JB092iB09p09023
Libraries: ACU

The continuum theory of mixtures provides a framework around which present knowledge of subglacial till can be organized. The proposed framework is provisional in two senses: the constitutive description of till will require improvement, and not all potentially significant processes have been included. Till is treated as a three-component mixture of water, clasts (coarse-grained solids), and fine-grained matrix solids. These components obey mass balance equations, and their behavior is subject to constitutive relations that describe such processes as Darcian water transport, fine-grained sediment transport, consolidation, shear deformation, dilatancy, and comminution. Five state variables uniquely determine the compressibility, permeability, shear strength, and other physical properties. Numerical solutions of the state evolutions equations illustrate that the properties of till are highly responsive to changes in the subglacial environment. (Au)

B, F
Compressive properties; Deformation; Glacial deposits; Mass balance; Mathematical models; Mechanical properties; Neutral stress; Permeability; Physical properties; Sediment transport; Strength; Stress

G0811
Trapridge Glacier, Yukon


Digital impulse radar for glaciology : instrumentation, modelling and field studies   /   Jones, F.H.M.   Clarke, G.K.C. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1987.
1 v.
Thesis (M.Sc.) - University of British Columbia, Vancouver, B.C., 1987.
Not seen by ASTIS. Citation from NSTP.
ASTIS record 28602.
Languages: English

Several aspects of impulse radar echo sounding of small glaciers are investigated. First, the ranges of values expected for conductivity and relative dielectric permittivity of glacier ice, glacier bed materials and mixtures of ice and rock are established. These parameters, and the fundamentals of electromagnetic wave propagation, are employed in a modelling scheme that examines the reflection of pulses from planar reflectors within the glacier. The glacier bed can be modelled as solid rock or unconsolidated debris and as either frozen or wet. A layer of mixed ice and rock between the glacier ice and bed can also be included. Signal enhancement, especially using multi-channel principal component analysis, is discussed. Discussion of practical application of the technique begins with the description of a portable microprocessor-controlled instrument capable of recording digitized echograms. Then results from experiments on Trapridge Glacier, Yukon Territory are presented. Surveys up to half a kilometer long with soundings at 1 to 20 m intervals were conducted. Bed topography is presented and locally anomalous sections are examined. Smaller-scale parameters such as the attenuation constant of ice and reflector properties are also extracted from the data. Subglacial and englacial temporal variations were studied by automatically recording echoes at one location every 20 minutes over a three-day period. Such experiments are to be used in the future in conjunction with other, concurrent, geophysical and hydrological investigations. (Au)

F
Glaciers; Instruments; Measurement; Radar; Theses; Thickness

G0811
St. Elias Mountains, Alaska/British Columbia/Yukon; Trapridge Glacier, Yukon


A short history of scientific investigations on glaciers   /   Clarke, G.K.C.
(Journal of glaciology, special issue, 1987, p. 4-24, ill.)
References.
ASTIS record 28152.
Languages: English
Libraries: ACU

Scientific investigations on valley glaciers engaged some of the greatest natural philosophers of the nineteenth century. Among these, Louis Agassiz has unique importance for he personifies the transition from the proto-scientific period of de Saussure and Scheuchzer to the scientific one of Forbes and his successors. In this brief history I have attempted to connect the achievements of the past 50 years with the aspirations of our predecessors. (Au)

V, F
Drilling; Flow; Glacier surges; Glaciers; Glaciology; History; Mass balance; Measurement; Research; Thermal regimes; Thickness

G01, G08
Canada; Europe; North America; Polar regions; Switzerland; United States


Characteristics of surge-type glaciers   /   Clarke, G.K.C.   Schmok, J.P.   Ommanney, C.S.L.   Collins, S.G.
(Journal of geophysical research, v. 91, no. B 7, June 10, 1986, p.7165-7180, ill., maps)
References.
ASTIS record 70000.
Languages: English
Web: doi:10.1029/JB091iB07p07165
Libraries: ACU

Glaciers can be divided into two classes according to their flow behavior: normal (relatively steady annually averaged flow rate) and surge-type (pronounced cyclic flow variations having a typical periodicity of 10-100 years). We have examined the population statistics of 2356 glaciers in the St. Elias Mountains, Yukon Territory, Canada, and estimate that 151 (6.4%) of these glaciers are surge-type. To explore how various glacier attributes are associated with surging, we compare the probability of surging associated with various subsets of the complete population to appropriate reference values. In this way, potential influences on surge tendency can be examined. For the 55 drainage basins analyzed, there is a pronounced spatial variation in the concentration of surge-type glaciers, but no obvious environmental control can be evinced. Within the study area the greatest concentration lies in the northern St. Elias Mountains, a region of high topographic elevation that is experiencing rapid tectonic uplift. Analysis of the influence of length on surge tendency reveals that long glaciers have a significantly greater probability of being surge-type than short glaciers. The surge probability increases monotonically from 0.61% for very short glaciers (0-1 km) to 65.1% for long glaciers (10-75 km). This result suggests that ice sheets and ice caps, or at least portions of them, should have a high probability of surging. Tributary glaciers have a greater tendency to surge than trunk glaciers, presumably because they may themselves be surge-type and may additionally participate in surges of the trunk glacier. The nonrandom geographical distribution of surge-type glaciers is not simply a consequence of the variation from basin to basin of the glacier length distribution. Surge-type glaciers tend to have a higher overall elevation than normal glaciers: the elevation of the highest point of the accumulation zone, the elevation of the snow line, and the elevation of the lowest point of the ablation zone, on average, exceed the corresponding elevations for normal glaciers. There is no significant difference between the overall slopes of surge-type and normal glaciers, although there is a tendency for surge-type glaciers to have greater slope in the accumulation zone and lesser slope in the ablation zone than normal glaciers. Although the prevalent flow direction for glaciers in the Yukon data set is to the north, surge-type glaciers tend to flow to the east and southeast. This orientation influence is probably explained by the fact that many of the longest glaciers also flow to the east and southeast. (Au)

F
Ablation; Accumulation; Drainage; Flow; Forecasting; Glacial melt waters; Glacier ice; Glacier surges; Glaciers; Mathematical models; Rivers; Size; Slopes; Spatial distribution; Temperature; Thermal regimes; Watersheds

G0811
St. Elias Mountains, Alaska/British Columbia/Yukon; Yukon


Measuring glacier-motion fluctuations using a computer-controlled survey system   /   Clarke, G.K.C.   Meldrum, R.D.   Collins, S.G.
(Canadian journal of earth sciences, v. 23, no. 5, May 1986, p. 727-733, ill.)
References.
ASTIS record 19649.
Languages: English
Web: doi:10.1139/e86-071
Libraries: ACU

We describe a computer-controlled, distance-measuring system designed for glacier-motion surveys. A Sharp PC-1500 pocket computer is used to control an AGA Geodimeter 122 infrared laser ranger. Slope distance and vertical angle are automatically measured and plotted at preselected time intervals and recorded on magnetic tape. As a demonstration, three field experiments were performed on Trapridge Glacier, Yukon Territory. In the first experiment the position of a glacier flow marker was measured at 1 min intervals for 39 h. The average velocity (toward the instrument) was found to be 2.99 mm/h. Subglacial water pressure was simultaneously measured at the flow marker site. For the duration of the survey, water pressure was low, and there is no clear relationship between pressure variations and glacier motion. In the second experiment the distance to a stationary target was measured at 1 min intervals for 9 h. The calculated motion of this target was -0.149 mm/h, giving an indication of the magnitude of uncorrected distance errors. The third experiment lasted 35 h and again involved measurements of glacier flow. The calculated target motion was 1.80 mm/h toward the instrument. (Au)

F
Electronic data processing; Flow; Glaciers; Velocity

G0811
Trapridge Glacier, Yukon


Professor Mathews, outburst floods, and other glaciological disasters   /   Clarke, G.K.C.
(Canadian journal of earth sciences, v. 23, no. 6, June 1986, p. 859-868, ill., maps)
References.
ASTIS record 18850.
Languages: English
Web: doi:10.1139/e86-088
Libraries: ACU

Misfortunes befalling the Granduc mining operation near Stewart, British Columbia, stimulated Professor Mathews' influential scientific contributions on subglacial hydrology. A series of violent floods from glacier-dammed Summit Lake menaced the transportation corridor between the Granduc ore concentrator and a tidewater dock at Hyder, Alaska. This unusual problem motivated the research of Mathews and later of Gilbert, who together laid the foundation for a greater understanding of the physics of outburst floods. The physical model that evolved from their research can be used to predict outburst flood magnitude and to cast light on the hydrology of ancient floods such as those from glacial Lake Missoula. (Au)

F, B
Floods; Forecasting; Glacier lake outbursts; Glacier lakes; Glacier surges; Glaciers; Palaeohydrology

G0811, G0821
British Columbia; Hazard Glacier, Yukon; Leduc Glacier, British Columbia; Missoula, Lake, Washington; Steele Glacier, Yukon; Stewart region, British Columbia; Summit Lake (58 39 N, 124 38 W), British Columbia


The 1981-1982 surge of Hazard Glacier, Yukon Territory   /   Clarke, G.K.C.   Collins, S.G.
(Canadian journal of earth sciences, v. 21, no. 3, Mar. 1984, p. 297-304, figures, tables)
References.
ASTIS record 14067.
Languages: English
Web: doi:10.1139/e84-032
Libraries: ACU

A surge of Hazard Glacier, believed to have started in 1981, displaced ice as much as 0.7 km. Before the surge, ice thickness was measured by radio echo sounding and temperatures were taken in three holes to the glacier bed. The glacier is subpolar with 10 m temperatures near -5.4° C, and temperature versus depth profiles show many anomalous features. We attribute these anomalies to various effects of past surges and to ablation at the upper surface. The interpretations are supported by simple calculations derived from dimensional analysis. Part of the glacier is warm based: at two sites the basal temperature was at the melting point; at the third site, upstream from the others, it was -2.70° C. (Au)

F
Glacier surges

G0811
Hazard Glacier, Yukon


Flow, thermal structure, and subglacial conditions of a surge-type glacier   /   Clarke, G.K.C.   Collins, S.G.   Thompson, D.E.
(Canadian journal of earth sciences, v. 21, no. 2, Feb. 1984, p. 232-240, ill.)
References.
ASTIS record 14049.
Languages: English
Web: doi:10.1139/e84-024
Libraries: ACU

Temperature measurements in a subpolar surge-type glacier reveal a distinctive thermal structure associated with the boundary between the ice reservoir and receiving areas. In the receiving area the glacier is cold based, but bottom temperature has increased as much as 0.5° C between 1981 and 1982, and the basal heat flux is roughly 10 times the expected geothermal flux. Water percolation through permeable subglacial material is the probable energy source. Deformation of the substrate could destroy this drainage system and trigger a surge. (Au)

F
Glacier surges; Glaciers; Temperature; Thermal regimes

G0811
Trapridge Glacier, Yukon; Yukon


UHF radar system for airborne surveys of ice thickness   /   Narod, B.B.   Clarke, G.K.C.
(Canadian journal of earth sciences, v. 20, no. 7, July 1983, p.1073-1086, figures, table)
References.
ASTIS record 12385.
Languages: English
Web: doi:10.1139/e83-096
Libraries: ACU NFSMO

We describe an 840 MHz pulsed radar system developed for airborne sounding of polar glaciers and ice caps. The system performance (ratio of transmitter power to minimum detectable signal) is 126 dB. A sampling time base converts the received signal to audio frequencies, and data are recorded in analogue form on magnetic tape. Computer-enhanced time sections for a glacier and an ice shelf are presented as examples. (Au)

F
Glaciers; Ice sheets; Ice shelf surveys; Ice shelves; Radar

G081
Canadian Arctic


Glacier outburst floods from "Hazard Lake", Yukon Territory, and the problem of flood magnitude prediction   /   Clarke, G.K.C.
(Journal of glaciology, v. 28, no. 98, 1982, p. 3-21, figures)
References.
ASTIS record 9098.
Languages: English
Libraries: ACU NFSMO

In August 1978 "Hazard Lake" released 19,620,000 cubic m of water through a subglacial tunnel beneath Steele Glacier, Yukon Territory, Canada. The discharge during the outburst flood was measured by recording lake level changes with time, and a peak discharge of approximately 640 m³/s was estimated from the data. We have attempted to model the 1978 flood from "Hazard Lake" using an adaptation of Nye's (1976) theoretical model for jokulhlaups from Grimsvotn. Our aim has been to calibrate the Nye model as a first step toward using it as a peak discharge estimator for other glacier-dammed basins. The agreement between out measured and simulated hydrographs is good, and we find that creep closure ... appears to play an insignificant role in limiting the discharge of "Hazard Lake". Release of thermal energy from the relatively warm lake water is the dominant factor contributing to tunnel enlargement. ... (Au)

F
Flood forecasting; Glacier lake outbursts; Mathematical models

G0811
Hazard Lake, Yukon; Steele Glacier, Yukon


Estimates of the magnitude of glacier outburst floods from Lake Donjek, Yukon Territory, Canada   /   Clarke, G.K.C.   Mathews, W.H.
(Canadian journal of earth sciences, v. 18, no. 9, Sept. 1981, p.1452-1463, ill., maps)
References.
ASTIS record 7340.
Languages: English
Web: doi:10.1139/e81-136
Libraries: ACU

Lake Donjek was a large reservoir formed when Donjek Glacier dammed Donjek River. Although the basin is empty at present, a minor advance of Donjek Glacier could again dam the river and impound approximately 234 x 10**6 m³ of water. Ice-dammed lakes are commonly unstable, giving rise to destructive floods called "jökulhlaups," or glacier outburst floods. Our aim in this paper is to estimate the likely magnitude of outburst floods from Lake Donjek so that the danger to downstream installations can be assessed. In attempting to estimate the maximum discharge from Lake Donjek, we use both the empirical formula of Clague and Mathews and a computer simulation model based on theoretical contributions from Nye. The September 1967 outburst flood from Summit Lake, B.C. is taken as a reference event against which predictions of the simulation model are compared. Our estimates for peak discharge from Lake Donjek lie in the range 677-5968 m³/s with values in the range 3968-5968 m³/s being considered most probable. (Au)

F
Drainage; Flood forecasting; Glaciation; Glacier lake outbursts; Hydrology; Lakes; River discharges

G0811
Donjek Glacier, Yukon; Donjek River, Yukon


Proceedings - Symposium on Processes of Glacier Erosion and Sedimentation, Geilo, Norway, 25-30 August 1980   /   Clarke, G.K.C. [Editor]
Cambridge : International Glaciological Society, 1981.
vi, 192 p. : ill. ; 30 cm.
(Annals of glaciology, v. 2, 1981)
ISBN 9502484-3-6
References.
ASTIS record 7252.
Languages: English
Libraries: ACU NFSMO

Papers presented are divided under four topics: erosional processes and features, sedimentation processes at the bed and terminus, marine processes, and, historical evidence of glacier erosion and sedimentation. (ASTIS)

F, A
Glacial erosion; Glacial landforms; Glacial transport; Sedimentation

G02, G13, G15
Antarctic regions; Arctic regions; Scandinavia


An estimate of the magnitude of outburst floods from Lake Donjek, Yukon Territory, Canada   /   Canada. Dept. of Indian Affairs and Northern Development [Sponsor]   Clarke, G.K.C.
Ottawa : DIAND, 1980.
90 p.
Not seen by ASTIS. Citation from NAP.
ASTIS record 27431.
Languages: English

F
Drainage; Floods; Glacier lake outbursts; Glacier lakes

G0811
Donjek, Lake, Yukon


Airborne UHF radio echo-sounding of three Yukon glaciers   /   Narod, B.B.   Clarke, G.K.C.
(Journal of glaciology, v. 25, no. 91, 1980, p. 23-31)
References.
ASTIS record 4803.
Languages: English
Libraries: ACU NFSMO

A high-resolution radio echo-sounder operating at a frequency of 840 MHz has been developed for airborne sounding of small and medium-sized polar glaciers and ice caps. The sounder uses a compact, high-gain antenna which suppresses valley-wall echoes and simplifies operation from light aircraft. Successful field trials were carried out on Rusty, Trapridge, and Hazard Glaciers, Yukon Territory, Canada. Results compare well with ice depths obtained from earlier ground-based soundings on Rusty and Trapridge Glaciers. The maximum ice thickness encountered was 200 m on Hazard Glacier. Owing to the high operating frequency, random scattering from inhomogeneities within the ice is a major cause of signal degradation. For this reason the sounder cannot penetrate great thicknesses of temperate or debris-rich ice. Spatial averaging, an immediate result of operating from a moving platform, reduces the effects of back-scattered "clutter". (Au)

F
Glaciers; Measurement; Radar; Thickness

G0811
St. Elias Mountains, Alaska/British Columbia/Yukon


Airborne radar sounding of Arctic icebergs   /   Rossiter, J.R.   Narod, B.B.   Clarke, G.K.C.
St. John's, Nfld. : C-CORE, 1979.
[24] p. : ill. ; 28 cm.
In: POAC 79 : the Fifth International Conference on Port and Ocean Engineering under Arctic Conditions, at the Norwegian Institute of Technology, August 13-18, 1979, proceedings. - [Trondheim, Norway : Norwegian Institute of Technology], 1979, v. 1, p. 289-305, ill.
(C-CORE publication, no. 79- 10)
Reviewed by ASTIS records 17289 and 17290.
References.
ASTIS record 3179.
Languages: English
Libraries: ACU NFSMO

Airborne radar was used in June 1978 to sound nine small-to-medium sized icebergs of various shapes near the coast of Labrador. Two different radar systems were used: a commercially developed monopulse system with a centre frequency of 80 MHz, and a glacier sounding radar operating at 840 MHz developed at the University of British Columbia. Each system was used from a Bell 206L helicopter, with the antennas mounted on the cargo hook next to the fuselage. Several passes were made over each iceberg at an altitude of 30 to 100 m above sea level. There was general agreement between results from the two radar systems. ... Airborne radar may offer a practical way to estimate quickly subsurface characteristics of icebergs. Simultaneous testing with other iceberg profiling techniques is required to validate its operational utility. (Au)

G, B
Icebergs; Radar

G09
Labrador waters


Ultrahigh frequency radio echo sounding of Yukon glaciers   /   Narod, B.B.   Clarke, G.K.C. [Supervisor]
[Vancouver, B.C. : University of British Columbia, 1979].
xii, 183 leaves : ill. (part. fold.) ; 28 cm.
(ProQuest Dissertations & Theses publication, no. NK46218)
Thesis (Ph.D.) - University of British Columbia, Vancouver, B.C., 1979.
Photocopy of typescript.
Bibliography: leaves 63-66.
ASTIS record 2945.
Languages: English
Libraries: ACU

A high-resolution radio echo sounder operating at a frequency of 840 MHz has been developed for sounding of small and medium-sized polar glaciers and ice caps. The sounder uses a compact, high-gain antenna which improves the system performance, suppresses valley wall echoes and simplifies operation from light aircraft. Successful field trials were carried out on the Rusty, Trapridge and Hazard Glaciers, Yukon Territory, Canada. ... (Au)

F
Glaciers; Physical properties; Radar; Theses

G0811
Hazard Glacier, Yukon; Rusty Glacier, Yukon; Trapridge Glacier, Yukon; Yukon


The dynamics of iceberg drift   /   Napoleoni, J.-G.P.   Clarke, G.K.C. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1979.
vi, 90 leaves : ill. ; 28 cm.
Thesis (M.A.Sc.) - University of British Columbia, Vancouver, B.C., 1979.
Photocopy of typescript.
Bibliography: leaves 59-63.
Appendix: Hot water drilling on a cold glacier / by Jean-Gerard P. Napoleoni and Garry K.C. Clarke. (Canadian journal of earth sciences, v. 15, no. 2, Feb. 1978, p. 316-321). - References.
ASTIS record 2944.
Languages: English
Libraries: ACU NFSMO

This thesis presents numerical models constructed for the prediction of iceberg drift. ... A discussion of the different possible drift models is presented. After commenting on the numerical results obtained with these models, a method is proposed for analyzing the past trajectory of an iceberg in order to determine coefficients necessary for predicting its drift. Hot water drilling on a cold glacier / by Jean-Gerard P. Napoleoni and Garry K.C. Clarke: An open circuit hot water drill using a propane water heater and a gasoline-driven pump is described. The drill is designed to reach depths of 300 m in cold ice for holes of 3 cm in diameter. A maximum drilling rate of 120 m/hr was obtained during field tests, and a 220 m hole was drilled in four hours. (Au)

G, F
Drilling; Glaciers; Icebergs; Mathematical models; Movement; Theses

G01, G0811
St. Elias Mountains, Alaska/British Columbia/Yukon


A creep instability analysis of the Antarctic and Greenland ice sheets   /   Cary, P.W.   Clarke, G.K.C.   Peltier, W.R.
(Canadian journal of earth sciences, v. 16, no. 1, Jan. 1979, p. 182-188, ill.)
References.
ASTIS record 1640.
Languages: English
Web: doi:10.1139/e79-016
Libraries: ACU

... Derived stability maps indicate that for the assumed rheology both ice sheets are completely stable; however, the stability of the coastal region of Wilkes Land in Antarctica is only marginal and cannot be accurately determined because of uncertainties in the data, especially basal shear stress. (Au)

F
Deformation; Ice sheets; Temperature

G01
Antarctic regions; Greenland


Hot water drilling in a cold glacier   /   Napoléoni, J.-G.P.   Clarke, G.K.C.
(Canadian journal of earth sciences, v. 15, no. 2, Feb. 1978, p. 316-321, ill.)
References.
Appendix.
ASTIS record 69964.
Languages: English
Web: doi:10.1139/e78-032
Libraries: ACU

An open circuit hot water drill using a propane water heater and a gasoline-driven pump is described. The drill is designed to reach depths of 300 m in cold ice for holes with a minimum diameter of 3 cm. A maximum drilling rate of 120 m/h was obtained during field tests, and a 220 m hole was drilled in 4 h. (Au)

F
Boreholes; Design and construction; Drilling; Equipment and supplies; Glaciers; Heat budgets; Instruments; Measurement; Radar; Specifications; Temperature; Thermal properties

G0811
Hazard Glacier, Yukon


Comparison of theoretical and observed temperature profiles in Devon Island ice cap, Canada   /   Paterson, W.S.B.   Clarke, G.K.C.
(Geophysical journal of the Royal Astronomical Society, v. 55, 1978, p. 615-632, ill., 1 map)
Appendix.
References.
ASTIS record 43920.
Languages: English
Web: doi:10.1111/j.1365-246X.1978.tb05931.x
Libraries: ACU

A non-steady-state theoretical model is used to predict the present variation of temperature with depth in two boreholes in the Devon Island ice cap, Arctic Canada. The boreholes are 300 m apart and one of them reaches bedrock. The heat transfer equation is solved numerically with the record of past temperatures obtained from measurements of the variations of oxygen-isotope ratio with depth in the cores as surface boundary condition. The effects of ice advection, refreezing of meltwater percolating from the surface (the amount of which is recorded in the cores), heating due to firn compaction and ice deformation, and heat flow in the bedrock below the ice sheet are all included in the model. The free parameters are geothermal heat flux, present surface temperature and heat loss at the surface which depends on the depth of meltwater penetration and other factors. Agreement between observed and predicted temperature-depth profiles is very close. Latent heat released by percolating meltwater is the predominating factor in determining the temperature distribution in the upper half of each borehole. The temperature distribution is insensitive to the value of the factor used to convert oxygen-isotope ratio to temperature. (Au)

F
Boreholes; Deformation; Density; Glacial melt waters; Heat transmission; Ice caps; Isotopes; Mathematical models; Temperature; Velocity

G0813
Devon Ice Cap, Nunavut


Notes on glaciology and the glaciers of Kluane Park   /   Clarke, G.K.C.
[S.l. : s.n.], 1977.
33 leaves : ill. ; 29 cm.
Indexed from a photocopy.
Prepared for a talk to Parks Canada, August 25, 1977.
ASTIS record 69963.
Languages: English
Libraries: ACU

Within the boundaries of Kluane Park lies one of the most rugged and spectacular glacier-covered landscapes in the world. Although the Greenland and Antarctic ice sheets have a far greater mass of ice, the incredible variety and comparative accessibility of the glaciers of the Icefield Ranges make them far more suitable for interpretive and scientific purposes. These notes are written with several aims in mind. The first is to discuss glaciers and glacier-associated problems which are at present most interesting to scientists. The second is to point out those glacier features which might be of particular interest to the general public and would therefore be suitable for use in the Kluane interpretive programme. It will become apparent, I hope, that many of the most interesting glacier features in Kluane Park would not even have been recognized were it not for the scientific work that has already been completed in the Park, and that many of the problems which scientists find the most interesting are also likely to interest the general public. (Au)

F, S, E, B
Climate change; Cores; Creep; Drilling; Effects of climate on ice; Effects of ice on climate; Flow; Glacier ice; Glacier lakes; Glacier surges; Glaciers; Glaciology; Isotopes; Mapping; Mass balance; Mathematical models; Measurement; Oxygen; Palaeoclimatology; Parks; Radar; Snow; Surveying; Temporal variations; Thickness; Tourist trade

G0811
Donjek Glacier, Yukon; Dusty Glacier, Yukon; Icefield Ranges, Yukon; Kaskawulsh Glacier, Yukon; Kluane National Park and Reserve, Yukon; Lowell Glacier, Yukon; Steele Glacier, Yukon


Strain heating and creep instability in glaciers and ice sheets   /   Clarke, G.K.C.   Nitsan, U.   Paterson, W.S.B.
(Reviews of geophysics and space physics, v. 15, no. 2, May 1977, p. 235-247, ill.)
References.
Appendix.
ASTIS record 42682.
Languages: English
Web: doi:10.1029/RG015i002p00235

Creep instability, the runaway increase of internal temperature and deformation rate, may affect the boundary condition at the base of glaciers and ice sheets and thus influence their flow and dimensions. We consider a simple slab model of heat transport in which three dimensionless parameters determine the relative importance of strain heating, ice advection normal to the surface, and boundary conditions. We find that an ice mass will be unstable if the strain-heating parameter exceeds a critical value which depends strongly on advection and boundary conditions. Critical values over the range of parameters appropriate to natural ice masses are presented. Accumulation (downward advection) or ablation (upward advection) affects the critical value by up to 5 orders of magnitude: ablation tends to reduce stability, and accumulation increases it. For an ice mass frozen to its bed, instability eventually raises the basal ice to melting point. This can restore thermal stability, but the ice mass will start to slide over its bed. If the strain-heating parameter exceeds a second, higher critical value, a layer of basal ice at melting point will form. We find that the conditions for instability are likely to exist in the accumulation and ablation zones of certain glaciers and ice sheets. However, times calculated for instability to develop are in the range 100 - 1,000 yr for glaciers and 1,000 - 10,000 yr for ice sheets. As these times exceed the normal residence time for ice in the ablation zone, it appears that instability is most likely to develop in the accumulation zone. This conclusion is reinforced by the fact that ablation increases the growth time for instability, whereas accumulation decreases it. The growth times quoted above are longer than the periods of most glacier surges, and thus creep instability is an unlikely surge mechanism. Unstable conditions may, however, obtain in East Antarctica and may have existed in the central part of ice age ice sheets. Surges of ice sheets triggered by creep instability may be possible. (Au)

F
Ablation; Accumulation; Creep; Flow; Glacier surges; Glaciers; Ice sheets; Mass balance; Mathematical models; Strain; Stress; Temperature

G01
Antarctic regions


History and bathymetry of a surge-dammed lake   /   Collins, S.G.   Clarke, G.K.C.
(Arctic, v. 30, no. 4, Dec. 1977, p. 217-224, ill., figure)
References.
Abstract in English, French and Russian.
ASTIS record 10366.
Languages: English
Web: http://pubs.aina.ucalgary.ca/arctic/Arctic30-4-217.pdf
Web: doi:10.14430/arctic2702
Libraries: ACU

A survey was made in 1974 of the small lake which had formed as a result of the surge advance of Steele Glacier, Yukon Territory, in 1965-68. Maximum lake level is controlled by a drainage channel which passes over rock near the hydrologic left margin of Steele Glacier. Since the surge advance of 1965-68 the lake has twice drained subglacially, producing minor outburst floods on Steele Creek and increasing the discharge of the Donjek River which crosses the probable route of the Alaska Highway pipeline. (Au)

G, F
Bathymetry; Floods; Glacier lake outbursts; Glacier surges

G0811
Donjek River, Yukon; Hazard Creek, Yukon; Steele Creek, Alaska/Yukon; Steele Glacier, Yukon


Post-surge temperatures in Steele Glacier, Yukon Territory, Canada   /   Clarke, G.K.C.   Jarvis, G.T.
(Proceedings of the Symposium on the Thermal Regime of Glaciers and Ice Sheets, Simon Fraser University, Burnaby, B.C., 1975. Journal of glaciology, v. 16, no. 74, 1976, p. 261-268, ill., map)
References.
ASTIS record 70002.
Languages: English
Libraries: ACU

Deep ice temperatures measured at four widely spaced sites on Steele Glacier show that the thermal regime was profoundly infuenced by the 1965-66 surge advance. Three of four measured temperature profiles are "anomalous" in that the upper 100 m of ice is far from thermal equilibrium. Water penetration during the surge is the probable cause of these anomalies. Insufficient data are available to predict the basal ice temperature. (Au)

F
Boreholes; Crevasses; Drainage; Drilling; Flow; Glacial melt waters; Glacier surges; Groundwater; Ice; Mathematical models; Measurement; Temperature; Temporal variations; Thermal regimes; Thickness; Water

G0811
Steele Glacier, Yukon


Thermal regulation of glacier surging   /   Clarke, G.K.C.
(Proceedings of the Symposium on the Thermal Regime of Glaciers and Ice Sheets, Simon Fraser University, Burnaby, B.C., 1975. Journal of glaciology, v. 16, no. 74, 1976, p. 231-250, ill., map)
References.
ASTIS record 70001.
Languages: English
Libraries: ACU

A necessary condition for a glacier to surge by thermal instability is that the glacier be cold with basal ice at or near the melting point. Deep temperature measurements show that two small surge-type glaciers in the Yukon Territory meet this requirement, but shallow measurements in three other surge-type glaciers suggest a temperate regime. If the later observations are accepted, not all surges are thermally controlled: if a single mechanism accounts for all surges it cannot be thermal instability. In this paper it is argued that thermal instability remains a viable mechanism for explaining surges of any cold glaciers, and that regardless of the underlying mechanism, thermal processes must at least have a major influence on the surge behavior of cold glaciers. Two numerical modelling experiments are described. The first involved a one-dimensional model which shows that thermal control can account for the remarkably constant surge cycle found in some glaciers. The second, a two-dimensional model of the time-dependent temperature structure of a surge-type glacier, shows that the relative amounts of temperate and cold basal ice can change considerably as the surge cycle progresses. This variation alone may be sufficient to explain surges, but even if this is not the case, thermal processes must affect the timing of surges in many cold glaciers. A compelling feature of the thermal instability mechanism is that it offers an explanation of the factors controlling the non-random geographical distribution of surge-type glaciers. For a glacier to have a cold surface and near-temperate bed, the ice thickness, temperature, and geothermal flux must be fortuitously related. (Au)

F
Boreholes; Creep; Friction; Glacier surges; Ice; Mathematical models; Measurement; Melting; Temperature; Temporal variations; Thermal regimes; Thickness

G0811
Rusty Glacier, Yukon; Trapridge Glacier, Yukon


The thermal regime of Trapridge Glacier and its relevance to glacier surging   /   Jarvis, G.T.   Clarke, G.K.C.
(Journal of glaciology, v. 14, no. 71, 1975, p. 235-250, ill., map)
References.
ASTIS record 69974.
Languages: English
Libraries: ACU

A deep-ice temperature measurement program has been conducted on Trapridge Glacier, Yukon Territory. Large regions of temperate ice are predicted at the base of the otherwise cold glacier. The glacier snout, frozen to bedrock, appears to act as an ice dam allowing the build up of an ice reservoir in the upper regions. Thermal regulation of the surges of Trapridge Glacier is suggested and the relevance of basal temperatures in large surging glaciers is discussed. (Au)

F
Ablation; Boreholes; Drilling; Equipment and supplies; Flow; Glacial melt waters; Glacier surges; Glaciers; Mathematical models; Measurement; Radar; Temperature; Thermal regimes; Thickness; Topography

G0811
Steele Glacier, Yukon; Trapridge Glacier, Yukon


Radio soundings on Trapridge Glacier, Yukon Territory, Canada   /   Goodman, R.H.   Clarke, G.K.C.   Jarvis, G.T.   Collins, S.G.   Metcalfe, R.
(Journal of glaciology, v. 14, no. 70, 1975, p. 79-84, ill., maps)
References.
ASTIS record 69973.
Languages: English
Libraries: ACU

As part of a program to study surge-type glaciers, a radar-depth survey, using a frequency of 620 MHz, has been made of Trapridge Glacier, Yukon Territory. Soundings were taken at 26 locations on the glacier surface and a maximum ice thickness of 143 m was measured. A rapid change in surface slope in the lower ablation region marks the boundary between active and stagnant ice and is suggestive of an "ice dam" or the water "collection zone" postulated by Robin and Weertman for surging glaciers. (Au)

F
Ablation; Aerial photography; Crevasses; Flow; Glacier surges; Glaciers; Measurement; Radar; Temporal variations; Thermal regimes; Thickness; Topography

G0811
Trapridge Glacier, Yukon


Radio echo soundings and ice-temperature measurements in a surge-type glacier   /   Clarke, G.K.C.   Goodman, R.H.
(Journal of glaciology, v. 14, no. 70, 1975, p. 71-78, ill., maps)
References.
ASTIS record 69971.
Languages: English
Libraries: ACU

Radio echo soundings on Rusty Glacier, a small surge-type glacier in Yukon Territory, reveal that the ice is considerably thicker than previously believed. A reinterpretation of deep ice-temperature measurements made in 1969 and 1970 suggests that a large zone of temperate basal ice exists. This result supports thermal instability as the surge mechanism for Rusty Glacier. (Au)

F
Boreholes; Glacier surges; Glaciers; Instruments; Measurement; Radar; Temperature; Thermal regimes; Thickness; Topography

G0811
Rusty Glacier, Yukon


Surging glacier studies   /   Clarke, G.K.C.
(Canadian alpine journal, v. 58, 1975, p. 38)
ASTIS record 63855.
Languages: English
Libraries: ACU

... For many years prior to its surge the Steele Glacier was nearly inactive, but in the early 1960s it began to show signs of increased activity which culminated in a spectacular seven mile ice movement. The main part of the surge is believed to have started in the fall of 1965. By the summer of 1966 the Steele's previously moraine-covered hummocky surface had become an alpinist's nightmare of crevasses and the ice was flowing at the startling rate of 50 ft per day. Time Magazine dubbed it the "galloping glacier" and scientists flocked to the Yukon as if to a gold rush. By 1967 the surge had stopped and interest in the Steele dwindled. Although much useful work was accomplished by glaciologists who observed the surge, the fundamental question of its cause remained unanswered. ... Work on the surface of Steele Glacier was thwarted until 1972 by the deep crevasses opened during the surge advance. For this reason initial field research by expeditions from UBC (beginning in 1968) was conducted on the Rusty and Trapridge Glaciers, two small glaciers near the Steele. Both the Rusty and Trapridge have surged in the past and are thought to be in a pre-surge condition. In view of their rarity it is remarkable that at least nine surge-type glaciers lie within a short distance of the Steele. All these glaciers must surely share some common feature which causes them to surge .... Geophysical studies on the Rusty and Trapridge were aimed at determining the channel geometry and ice temperature, two factors which are known to have a strong influence on glacier flow rate. ... Both glaciers proved relatively thin and no recorded depths exceeded 500 ft. ... Temperature measurements in the Rusty and Trapridge Glaciers appear to give a consistent picture. Both glaciers have cold ice near the surface (around -60°C on average) and the temperature warms to near the melting point as the glacier bed is approached. Large patches of ice covering the glacier bed appear to be at the melting temperature so that within these zones of warm basal ice the glacier is not frozen to its bed and sliding can occur. ... A cycle of quiescence and advance will occur if the bed temperature oscillates near the melting point of ice. When most of the bed is frozen the glacier cannot slide and remains inactive; when the warm ice zone is extensive, the glacier is able to slide. Basal temperature turns out to depend on the surface temperature, ice thickness and the rate at which heat flows from the bedrock into bottom ice. A quiescent glacier will tend to thicken and this leads to a warming of the bed as cold surface ice recedes from it. Eventually a large portion of the bed reaches the melting temperature and the sliding rate will increase, causing the snout to advance and the glacier to thin; this marks the onset of a surge. As the glacier thins, cold surface ice moves toward the bed and eventually cools it below the melting point, stopping the advance. The surge periodicity of a particular glacier would depend in a complex way on the surface temperature of the glacier, the rate of heat flow into the glacier from the underlying rock and the rate that the glacier thickens during the quiescent stage. Only glaciers in relatively high latitudes, such as those along the Alaska-Yukon border, have cold surface ice; this in combination with other factors might account for the non-random geographic distribution of surge-type glaciers. A drilling program begun in 1972 on Steele Glacier is still in the early stages but initial ice temperature measurements are at least compatible with the requirements for a thermal control mechanism. ... Perhaps there are several different causes for glacier surging or perhaps the idea of thermal control is simply wrong. At this point one can only conclude that the problem of glacier surging is still a long way from being solved. (Au)

F
Boreholes; Flow; Glacier surges; Glaciers; Heat transmission; Radar; Size; Temperature; Thermal regimes; Thickness; Velocity

G0811
Rusty Glacier, Yukon; Steele Glacier, Yukon; Trapridge Glacier, Yukon


Thermal effects of crevassing on Steele Glacier, Yukon Territory, Canada   /   Jarvis, G.T.   Clarke, G.K.C.
(Journal of glaciology, v. 13, no. 68, 1974, p. 243-254, ill., map)
References.
Appendices.
ASTIS record 69969.
Languages: English
Libraries: ACU

Ice temperature measurements have been made in Steele Glacier to a depth of 114 m. All measured temperatures were below 0°C, the coldest being -6.5°C at a depth of 114 m. The temperature profile indicates an anomalously warm layer of ice between 30 m and 50 m, which is probably due to the freezing of water in crevasses opened during the 1965-66 surge. A two-dimensional model of a cold glacier with partially water-filled crevasses predicts temperature profiles very similar to that observed. (Au)

F
Boreholes; Crevasses; Drilling; Formation; Glacier surges; Glaciers; Ice; Mathematical models; Measurement; Temperature; Thermal regimes

G0811
Steele Glacier, Yukon


"Fox Glacier" in Yukon Territory is now Rusty Glacier   /   Clarke, G.K.C.   Crossley, D.J.
(Journal of glaciology, v. 11, no. 63, 1972, p. 456-567)
References.
ASTIS record 71355.
Languages: English
Libraries: ACU

Some of your readers will be delighted to learn that the glacier unofficially named "Fox Glacier" in Yukon Territory has now been officially named Rusty Glacier by the Canadian Permanent Committee on Geographical Names. The unofficially named "Jackal" and "Hyena Glaciers" are now officially Backe and Trapridge Glaciers respectively. The designations "Fox", "Jackal" and "Hyena" had respectable if not venerable roots. In 1963 Austin Post (personal communication) assigned these names for reference purposes to three small surging glaciers in the St Elias Mountains, Canada. The following year he completed a map on which these names were used, and although the map was not published it was widely circulated. Post was inspired to use canine names by the proximity of these glaciers to the unofficially named "Wolf Creek Glacier", now Steele Glacier. In 1968 Rusty Glacier was among a small number of Canadian glaciers selected for special study during the International Hydrological Decade; a substantial literature therefore exists in which the unofficial designation "Fox Glacier" was used. To prevent further confusion with other Fox Glaciers we have compiled a fairly complete list of these references, omitting annual reports on field work in the St Elias Mountain Ranges contained in the Annual Report of the Arctic Institute of North America, Arctic, the Canadian Alpine Journal, the Canadian Geophysical Bulletin, and Ice (Nielsen, 1968; Paterson, 1968; Meier and Post, 1969, p. 816-17; Nielsen, 1969; Post, 1969; Clarke and Classen, 1970; Crossley and Clarke, 1970; West and Krouse, 1970; Clarke, [1971]; Classen and Clarke, 1971; Collins, 1971; Krouse, [1971]; Paterson, 1971). (Au)

F
Geographical names; Glaciers

G0811
Backe Glacier, Yukon; Rusty Glacier, Yukon; Trapridge Glacier, Yukon


Thermal drilling and ice-temperature measurements in the Rusty Glacier   /   Classen, D.F.   Clarke, G.K.C.
(Icefield Ranges Research Project, scientific results, v. 3, 1972, p. 103-116, ill., maps)
References.
Appendices.
ASTIS record 66476.
Languages: English
Libraries: ACU

During the summer of 1969 a thermal drilling and deep-ice temperature measurement program was carried out on the Rusty Glacier. The thermal drilling produced seven instrumented holes at six locations on the glacier, three reaching bedrock. Temperature measurements indicated that the glacier was below the pressure-melting point throughout, and that evidence of a disturbed thermal regime existed. Estimates of geothermal heat flow were determined, and an anomalous value of 4.73 µ cal/cm² sec was obtained. Bottom temperature models were developed which indicate the possibility of basal melting. (Au)

F
Boreholes; Drilling; Flow; Glacier surges; Glaciers; Heat transmission; Instruments; Measurement; Melting; Physical properties; Spatial distribution; Surface properties; Temperature; Thermal properties; Thermal regimes; Velocity

G0811
Rusty Glacier, Yukon


Gravity and shallow-ice temperature measurements on the Rusty Glacier   /   Crossley, D.J.   Clarke, G.K.C.
(Icefield Ranges Research Project, scientific results, v. 3, 1972, p. 93-101, ill., maps)
References.
Appendices.
ASTIS record 66475.
Languages: English
Libraries: ACU

The Rusty Glacier has a history of surging but is at present quiescent. In 1968 a gravity survey indicated the glacier has a maximum depth of 88 m. Near-surface temperature measurement identify the Rusty as a subpolar glacier. (Au)

F, E
Density; Flow; Glacier surges; Glaciers; Gravity measurement; Instruments; Mathematical models; Quality assurance; Snow cover; Surface temperature; Temporal variations; Thermal regimes; Thickness; Velocity

G0811
Rusty Glacier, Yukon


Basal hot spot on a surge type glacier   /   Classen, D.F.   Clarke, G.K.C.
(Nature, v.229, no.5285, 12 Feb. 1971, p. 481-483, ill., map)
References.
ASTIS record 69967.
Languages: English
Web: doi:10.1038/229481a0
Libraries: ACU

DEEP temperature measurements of ice on the Fox Glacier, Yukon, indicate a zone of basal ice at the pressure melting point and the discovery of this temperate basal ice supports surge theories which require basal melting. (Au)

F
Boreholes; Drilling; Flow; Glacier surges; Glaciers; Heat transmission; Instruments; Measurement; Melting; Temperature; Temporal variations; Thermal properties; Thermal regimes; Thickness; Topography

G0811
Rusty Glacier, Yukon


The Fox Glacier project   /   Clarke, G.K.C.   Classen, D.F.
(Canadian geographical journal, v. 81, no. 1, July 1970, p. 26-29, ill., maps)
ASTIS record 71336.
Languages: English

... In an effort to explain the mechanism at work in surging glaciers, glaciologists from Canada and the United States decided to make a concentrated effort upon a single pre-surge glacier. Early in 1967, the Fox Glacier, a small glacier in the vicinity of the Steele, was selected as a promising candidate. Inspection of the moraines and glacier surface revealed many features in common with the Steele Glacier before its surge. The Fox Glacier appeared to be a surge-type glacier in a period of quiescence. Of additional interest was the surge of the nearby Jackal Glacier which was overriding a lower section of the Fox. The logistic problems associated with establishing and maintaining an efficient scientific camp in an inhospitable region over 50 miles from the Alaska Highway are formidable. However the Icefield Ranges Research Project, a joint endeavor of the American Geographical Society and the Arctic Institute of North America, specializes in such unusual chores. From the IRRP base on the southern shore of Kluane Lake helicopters and ski-wheel planes supplied the glacier camp with items ranging from freeze-dried strawberries to electrical generators. The Fox Glacier is by no means the sole interest of the Icefield Ranges Research Project. Since 1961 IRRP has instigated an ambitious multidisciplinary study of the St. Elias Mountains in terms of the total environment. From the outset educational as well as scientific goals have been stressed: .... (Au)

F
Flow; Glacier surges; Glaciers; Gravity measurement; Instruments; Mapping; Measurement; Melting; Movement; Temperature; Thickness; Velocity

G0811
Rusty Glacier, Yukon; Steele Glacier, Yukon


Gravity measurements on "Fox Glacier", Yukon Territory, Canada   /   Crossley, D.J.   Clarke, G.K.C.
(Journal of glaciology, v. 9, no. 57, 1970, p. 363-374, ill., maps)
References.
Appendix.
ASTIS record 69968.
Languages: English
Libraries: ACU

"Fox Glacier", Yukon Territory, has a history of surging and is at present in a quiescent period. In 1968 a gravity survey was carried out over the glacier, in order to find ice depths. The results indicate the glacier is thin with a maximum depth of 88 m. (Au)

F
Glacial melt waters; Glacier surges; Glaciers; Gravity measurement; Instruments; Mathematical models; Measurement; Radar; Seasonal variations; Surface temperature; Thickness; Topography

G0811
Rusty Glacier, Yukon


Geophysical measurements on the Kaskawulsh and Hubbard Glaciers, Yukon Territory   /   Clarke, G.K.C.
Montreal : Arctic Institute of North America, 1967.
36 p. : ill., maps ; 25 cm.
(Technical paper - Arctic Institute of North America, no. 20)
(Icefield Ranges Research Project, scientific results, v. 1, 1969, p. 88-106, ill., maps)
ISBN 0-919034-36-5
One folding map attached to the back inside cover (29 × 49 cm folded to 24 × 15 cm).
References.
The text and titles of the AINA technical paper and IRRP article differ slightly.
IRRP title: "Geophysical measurements on the Kaskawulsh and Hubbard Glaciers".
The text of the IRRP article refers to a map that is printed inside the fold-out back cover of the volume.
ASTIS record 32740.
Languages: English
Libraries: ACU

Gravity and seismic measurements made in the summer of 1963 were used to determine ice thickness in the divide region of the Kaskawulsh and Hubbard Glaciers (60° 45N, 139° 40W) in the St. Elias Mountains of the Yukon Territory, Canada. Gravity differences were measured for a network of 107 gravity stations and Bouguer anomalies ranged from -199.8 mgal to -162.9 mgal. Crude ice-thickness calculations were made from these results assuming the glacier was an infinite slab. Seismic refraction lines on the Kaskawulsh and Hubbard Glaciers gave a firn thickness of approximately 40 m and an average P-wave velocity of 3710 ±20 m/sec. One hundred seismic reflection stations were occupied and, discounting poor results, the maximum ice thicknesses found were 778 m at Stake 1 on the Kaskawulsh Glacier and 539 m at Stake 29 on the Hubbard Glacier. The maximum surface flow rates measured were 150 m/yr at Stake 1 on the Kaskawulsh Glacier and 132 m/yr at Stake 44 on the Hubbard. A close relationship was found between geophysically-determined ice thicknesses and surface flow measurements. The flow line and the line of the valley center proved to be roughly coincident, although flow was complicated by tributary glaciers. The topographic divide was also the flow divide but no corresponding bedrock divide was found. (Au)

F, B
Crystals; Density; Firn; Flow; Glaciers; Gravity measurement; Instruments; Seismic surveys; Spatial distribution; Thickness; Velocity

G0811
Hubbard Glacier, Alaska/Yukon; Kaskawulsh Glacier, Yukon


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