Stabilizing feedbacks in glacier-bed erosion

Glaciers often erode, transport and deposit sediment much more rapidly than nonglacial environments, with implications for the evolution of glaciated mountain belts and their associated sedimentary basins. But modelling such glacial processes is difficult, partly because stabilizing feedbacks similar to those operating in rivers have not been identified for glacial landscapes. Here we combine new and existing data of glacier morphology and the processes governing glacier evolution from diverse settings to reveal such stabilizing feedbacks. We find that the long profiles of beds of highly erosive glaciers tend towards steady-state angles opposed to and slightly more than 50 per cent steeper than the overlying ice–air surface slopes, and that additional subglacial deepening must be enabled by non-glacial processes. Climatic or glaciological perturbations of the ice–air surface slope can have large transient effects on glaciofluvial sediment flux and apparent glacial erosion rate.

[1]  Matt Nolan,et al.  Ice-thickness measurements of Taku Glacier, Alaska, U.S.A., and their relevance to its recent behavior , 1995, Journal of Glaciology.

[2]  D. Lawson.  Semdimentological Analysis of the Western Terminus Region of the Matanuska Glacier, Alaska, , 1979 .

[3]  Johan Anderson.  Glacimarine environments: Processes and sediments, Edited by J. A. Dowdeswell and J. D. Scourse, Geological Society Special Publication 53, London 1990. No. of pages: 423. Price: £75.00 ($125.00) (hardback) , 1991 .

[4]  R. Alley,et al.  Preliminary results of tritium analyses in basal ice, Matanuska Glacier, Alaska, U.S.A.: evidence for subglacial ice accretion , 1996, Annals of Glaciology.

[5]  D. Lawson.  Glaciohydrologic and Glaciohydraulic Effects on Runoff and Sediment Yield in Glacierized Basins , 1993 .

[6]  R. Hooke.  Positive feedbacks associated with erosion of glacial cirques and overdeepenings , 1991 .

[7]  Dorothy K. Hall,et al.  CHANGES OF GLACIERS IN GLACIER BAY, ALASKA, USING GROUND AND SATELLITE MEASUREMENTS , 1995 .

[8]  R. Alley,et al.  Glaciohydraulic supercooling: a freeze-on mechanism to create stratified, debris-rich basal ice: I. Field evidence , 1998, Journal of Glaciology.

[9]  B. Hallet,et al.  Influence of rapid glacial retreat on the rate of erosion by tidewater glaciers , 2002 .

[10]  V. Pohjola,et al.  Hydrology of a segment of a glacier situated in an overdeepening, Storglaciären, Sweden , 1994, Journal of Glaciology.

[11]  R. Alley,et al.  Sediment, glaciohydraulic supercooling, and fast glacier flow , 2003, Annals of Glaciology.

[12]  Olav Slaymaker,et al.  Glacio-Fluvial Sediment Transfer: An Alpine Perspective , 1988 .

[13]  J. Strnad,et al.  A simple theoretical model of a bungee jump , 1997 .

[14]  L. Lliboutry.  Modifications to the Theory of Intraglacial Waterways for the Case of Subglacial Ones , 1983 .

[15]  Ó. Knudsen,et al.  Glaciohydraulic supercooling in Iceland , 2002 .

[16]  J. H. Mackin.  CONCEPT OF THE GRADED RIVER , 1948 .

[17]  Kelin X. Whipple,et al.  Glacial erosion and relief production in the Eastern Sierra Nevada, California , 2002 .

[18]  R. Powell,et al.  Flux of debris transported by ice at three Alaskan tidewater glaciers , 1996 .

[19]  Steven A. Arcone,et al.  12- to 100-MHz depth and stratigraphic profiles of temperate glaciers , 2000, International Conference on Ground Penetrating Radar.

[20]  B. Hallet,et al.  Rates of erosion and sediment evacuation by glaciers: A review of field data and their implications , 1996 .

[21]  N. Iverson.  Potential effects of subglacial water-pressure fluctuations on quarrying , 1991, Journal of Glaciology.

[22]  Richard B. Alley,et al.  How glaciers entrain and transport basal sediment: Physical constraints , 1997 .

[23]  R. Alley,et al.  Glaciohydraulic supercooling: a freeze-on mechanism to create stratified, debris-rich basal ice: II. Theory , 1998, Journal of Glaciology.

[24]  David R. Montgomery,et al.  Valley formation by fluvial and glacial erosion , 2002 .

[25]  B. Hallet,et al.  Glacial quarrying: a simple theoretical model , 1996, Annals of Glaciology.

[26]  O. J. Ferrians,et al.  Late Wisconsin and Recent History of the Matanuska Glacier, Alaska , 1961 .

[27]  Is erosion by deforming subglacial sediments significant? (Toward till continuity) , 1996 .

[28]  R. Alley,et al.  Bedload component of glacially discharged sediment: Insights from the Matanuska Glacier, Alaska , 2001 .

[29]  D. Easterbrook.  Surface processes and landforms , 1992 .

[30]  Julian A. Dowdeswell,et al.  Glacimarine Environments: Processes and Sediments , 1990 .