Connecting hydrology and evolving properties of subglacial sediment beneath Russell Glacier, Greenland
Abstract
Seasonal flow variations have been observed on a large number of glaciers in Greenland. Typical for many glaciers is a speed up during spring, a slow down during summer, and a return to the winter velocity during fall. The drainage of supra-glacial lakes, which has been observed together with transient changes in ice flow, is another common characteristic of the Greenland Ice Sheet. The subsequent processes taking place at the bed of the ice sheet is, however, hindered by a paucity of data and observations. Recent advances in numerical modeling suggest that the hydrological system of glaciers overriding a hard bed responds to changes in discharge and that slowdown occurs when there is a switch from distributed to channelized drainage, yet the possible role of subglacial sediment in storing water and modulating ice flow remains unknown. This is problematic because large areas of the Greenland Ice Sheet could be underlain by such sediment. Here, we study the potential mechanisms responsible for seasonal flow changes for glaciers overriding soft sediments with a particular focus on sediment properties evolving from changing hydrological conditions. Our chosen site of investigation is the land-terminating Russell Glacier on the West Coast of Greenland where geophysical surveys have revealed the presence of subglacial sediment with a typical porosity of 30-35% and a thickness of about 20m. We have estimated the current distribution of basal stress beneath Russell glacier from an inversion of the observed surface velocity with the Glimmer-CISM higher order ice flow model. This inversion showed production of meltwater at a rate of 0.1 m/yr, which is consistent with the presence of weak subglacial sediment. To develop an understanding of the implication of the presence of weak subglacial sediment, we used forward simulations with the Glimmer-CISM model with basal conditions prescribed according to sedimentary processes and a regional hydrology system fed by supraglacial meltwater. Application to Russell Glacier and preliminary results indicate that glaciers overriding soft sediment may experience seasonal flow variations when a high rate of water is temporarily injected to its bed. Seasonal ice flow dynamics for glaciers overriding a soft bed may thus be a result of water pressure variations associated with temporal storage of meltwater in subglacial sediments.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.C31B0595B
- Keywords:
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- 0720 CRYOSPHERE / Glaciers;
- 0726 CRYOSPHERE / Ice sheets;
- 0766 CRYOSPHERE / Thermodynamics;
- 0798 CRYOSPHERE / Modeling