Quaternary relief generation by polythermal glacier ice

Abstract

AbstractThe juxtaposition of wet‐based erosive ice in valleys and cold‐based, non‐erosive ice atop felsenmeer‐covered interfluve plateaus has generated relief in the Torngat Mountains of northeastern Canada. Measurements of in situ terrestrial cosmogenic nuclide (TCN) concentrations from 31 bedrock sites, coupled with soils and geomorphology, indicate that erosion of the valleys has been >2 m during a single glacial–interglacial cycle. However, on summit plateaus the long‐term (over several glacial–interglacial cycles) erosion rate is <1·4 m Ma−1. TCN ratios reveal that the exposure plus ice‐cover history retained on some summit surfaces probably spans more than 800 ka despite complete ice cover as recently as 11 ka. A thermodynamic ice sheet model with a basal water calculation is used to calculate the sliding distance normalized by the duration of ice cover for the region. We formulate a general glacial erosion rule for the Torngat Mountains, which correlates TCN‐derived erosion rates for terrain once partially covered by cold‐based ice with modelled average ice basal sliding velocities. Erosion rates vary linearly with average sliding velocity by a glacial erosion coefficient of 5 × 10−7. Due to the significant distribution of cold‐based ice cover in this high latitude region, our estimates of net regional glacial erosion and glacial erosion coefficient are orders of magnitude lower than a previously published value. Copyright © 2005 John Wiley & Sons, Ltd.