Glacier-permafrost interactions: Processes, products and glaciological implications

Glaciers and permafrost represent key components of the global cryosphere. Widely held assumptions that: (1) they are largely mutually exclusive and, (2) glaciers resting on permafrost are slow moving and geomorphologically ineffectual have meant that glacier-permafrost interactions have been given little attention within the research literature. Recent research, however, has demonstrated that such interactions are likely to have been more extensive than previously thought, particularly during periods of ice-sheet growth when glaciers would have advanced over pre-existing permafrost. Work in both modern and ancient environments has revealed that subglacial processes such as basal sliding and subglacial sediment deformation can remain active at temperatures below the pressure melting point due to the persistence of premelted liquid water. Consequently, cold-based glaciers resting on permafrost are potentially more dynamic than previously thought and are capable of creating subglacial features typically viewed as only forming beneath warm-based ice. In addition, the active coupling of cold-based ice with ice-marginal permafrost means such ice masses are capable of deforming sediments and occasionally bedrock to depths of tens or even hundreds of meters and are commonly associated with the development of a range of distinctive ice-marginal landforms including push or thrust moraines and hummocky or controlled moraines. This reflects the influence of permafrost on the entrainment of debris-rich basal ice as well as the hydraulic transmissivity of the groundwater system and the associated porewater pressures within the substrate. This review considers the key characteristics of permafrost and its formation, likely extent and rheological behaviour within glacial environments. Traditional conceptions regarding the motion and landscape impact of cold-based glaciers resting on permafrost are considered before their re-examination in light of recent work demonstrating the operation of basal processes at sub-freezing temperatures. The implications for our understanding of the dynamics of glaciers and ice sheets as well as landforms and sedimentary sequences indicative of glacier-permafrost interactions are explored and exemplified with reference to modern and ancient glacial environments. Gaps in our existing knowledge are identified and profitable areas for future research suggested. (C) 2012 Elsevier B.V. All rights reserved.