The Influence of Bedrock Fracture Characteristics on Glacier Dynamics
Abstract
During a glacier surge ice speeds can increase by orders of magnitude above quiescence. Processes that take place during a surge have been well documented, and point clearly to the importance of basal conditions. Yet, it remains unclear if basal conditions are somehow fundamentally different between ordinary glaciers and glaciers prone to surging. Identifying such differences might help explain the spatial distribution of surge-type glaciers that cannot be explained by other glacier attributes or environmental envelopes alone. In this study we test the hypothesis that geotechnical characteristics of the bedrock give rise to basal conditions that allow a glacier to surge. We measure bedrock discontinuity geometric properties from outcrops at the margins of eight surge-type and eight ordinary glaciers in the St. Elias Mountains of Yukon, Canada. Using photographs of the outcrops we digitally trace discontinuities, and use purpose-built software to quantify two-dimensional indicators of bedrock quality such as the linear intensity and aerial density of discontinuities. We analyse the results through statistical pairwise comparison tests that control for glacier-type (surge-type vs. ordinary) and bedrock lithology. Our results indicate that surge-type glaciers in our study area are associated with less fractured bedrock than that in the basins of ordinary glaciers. In an attempt to explain this unexpected result, we consider the complex relationship between discontinuity spacing, clast production, and till formation. We hypothesize that the excessive drag that leads to surge reservoir development during quiescence does not result from ice-till processes, but rather from clast-bed interactions within a clast-rich till-transition zone. We suggest that the extent and location of this zone are controlled by the spacing of discontinuities in the bedrock, and are key controls on the development of a surge reservoir.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.C31B..02C
- Keywords:
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- 0720 Glaciers;
- CRYOSPHERE;
- 0726 Ice sheets;
- CRYOSPHERE;
- 0774 Dynamics;
- CRYOSPHERE;
- 0776 Glaciology;
- CRYOSPHERE