Abstract
Abstract Ice-marginal glaciated landscapes demarcate former boundaries of the continental ice sheets. Throughout circumpolar regions, permafrost has preserved relict ground ice and glacigenic sediments, delaying the sequence of postglacial landscape change that transformed temperate environments millennia earlier. Here we show that within 7 × 106 km2 of glaciated permafrost terrain, extensive landscapes remain poised for major climate-driven change. Across northwestern Canada, 60–100-km-wide concentric swaths of thaw slump–affected terrain delineate the maximum and recessional positions of the Laurentide Ice Sheet. These landscapes comprise ∼17% of continuous permafrost terrain in a 1.27 × 106 km2 study area, indicating widespread preservation of late Pleistocene ground ice. These thaw slump, relict ground ice, and glacigenic terrain associations are also evident at the circumpolar scale. Recent intensification of thaw slumping across northwestern Canada has mobilized primary glacial sediments, triggering a cascade of fluvial, lacustrine, and coastal effects. These geologically significant processes, highlighted by the spatial distribution of thaw slumps and patterns of fluvial sediment mobilization, signal the climate-driven renewal of deglaciation and postglacial permafrost landscape evolution.
Highlights
Ice-marginal glaciated landscapes demarcate former boundaries of the continental ice by glacio-isostatic adjustments, and climatesheets
We propose that in circumpolar regions, cold climate and permafrost has maintained glacial landscapes including moraine complexes and glaciofluvial, glaciolacustrine, and glaciomarine deposits in a GEOLOGY, April 2017; v. 45; no. 4; p. 371–374 | Data Repository item 2017106 | doi:10.1130/G38626.1 | Published online 7 February 2017
The mapping of a 1,274,625 km2 area of northwestern Canada reveals that the distribution of slump-affected terrain is remarkably well constrained by the maximum extent of the Laurentide Ice Sheet (LIS) (Fig. 2A)
Summary
Ice-marginal glaciated landscapes demarcate former boundaries of the continental ice by glacio-isostatic adjustments, and climatesheets. Recent phic processes can expose ground ice directly intensification of thaw slumping across northwestern Canada has mobilized primary glacial to surface energy fluxes, rapidly degradsediments, triggering a cascade of fluvial, lacustrine, and coastal effects These geologically ing ice-rich terrain and modifying slope and significant processes, highlighted by the spatial distribution of thaw slumps and patterns of valley configurations (Fig. 1; Fig. DR1 in fluvial sediment mobilization, signal the climate-driven renewal of deglaciation and postgla- the GSA Data Repository). Coupled climate-terrestrial models predict Dyke and Evans, 2003) These vast stores of fro- reworked glacial deposits in temperate regions widespread degradation of near-surface perma- zen sediments host thick layers of ground ice, frost over the century (IPCC, 2013), indicating that thawing of ice-rich terrain (thermokarst) will be the fundamental mechanism of circumpolar landscape change (Kokelj and Jorincluding massive segregated ice and buried glacier ice (Mackay, 1971; Murton et al, 2005; Evans, 2009). A quantitative geomorphic framework for determining the nature and intensity of thermokarst remains a critical gap in predicting the environmental conse-
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