Quaternary relief generation by polythermal glacier ice

Abstract

The 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. 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. 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.

Lateglacial and Holocene cosmogenic surface exposure age glacial chronology and geomorphological evidence for the presence of cold‐based glaciers at Nevado Sajama, Bolivia

“…Staiger et al (2005) indicate that cold-based ice: (1) deposits bouldery moraines or ground moraine;…”

Glacier change from the early Little Ice Age to 2005 in the Torngat Mountains, northern Labrador, Canada

“…Contrasting degrees of glacial erosion between the uppermost mountain peaks and lower valley bottoms suggest that non erosive, coldbased ice occupied the highest Torngat Mountains during the last glacial maximum while highly erosive, warm-based ice filled the lower valleys (e.g., Marquette et al, 2004;Staiger et al, 2005). Many valleys also contain moraine sequences leading from empty or ice-occupied cirques, signifying a history of glacial recession in the region.…”

Using a GIS filtering approach to replicate patterns of glacial erosion

“…Peulvast, 1985;Lidmar-Bergström et al, 2000;Fjellanger and Sørbel, 2007). In high-relief alpine terrain these surfaces are often well-defined but relatively fragmentary (Kleman and Stroeven, 1997;Fabel et al, 2002;Marquette et al, 2004;Staiger et al, 2005;Bonow et al, 2006;LidmarBergström et al, 2007;Nesje et al, 2007;. In more subdued relief, however, the identification of relict surface boundaries is more subjective (Kleman and Stroeven, 1997;Clarhäll, 2002;Hättestrand and Stroeven, 2002), in part because such surfaces are often covered in a blanket of glacigenic material .…”