A mass movement origin for cirques

• Published in: Earth surface processes and landforms Vol. 31; no. 9; pp. 1129 - 1148
• Main Authors: Turnbull, Jill M., Davies, Timothy R. H.
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.08.2006; Wiley
• Subjects: Bgi / Prodig; cirques; deep-seated rock slope failures; Geomorphology; glacial erosion; Physical geography; rock avalanches; Slopes; subaerial erosion; New Zealand; South Island; Erosion rate; Cirque; Mountain; Glacial features; Quaternary; Mass movement; Palaeoclimatology; Glacial erosion; Avalanche
• ISSN: 0197-9337; 1096-9837
• DOI: 10.1002/esp.1324

The glacial process of cirque initiation, whereby small initial hillslope hollows grow by nivation until snow can form glacier ice, and ice motion then enlarges the hollow to a fully developed cirque, appears to have difficulty explaining the creation of large cirques in the time available during Quaternary glaciations, at the rates at which glaciers are reported to erode rock, and in rapidly uplifting mountain ranges. It also has difficulty explaining the striking proliferation of cirques in Fiordland, South Island, New Zealand, an area of harder rock and less glaciation than the nearby cirque‐poor area of South Westland. Here we show that cirques can be initiated as large, deep‐seated, often coseismic rock slope failure source area depressions in which snow may accumulate to form cirque glaciers, which can then remove detritus from, smooth, and enlarge the cirque. We present an example of a classically shaped cirque that has never held a glacier. We show that many similarities between the locations, sizes and shapes of rock slope failure source area depressions and cirques are understandable on this basis, as is the occurrence of cirques in presently aseismic intraplate locations and their relative paucity in actively uplifting ranges. The extent to which cirques may be of mass movement origin has implications for their value as palaeoclimatic indicators. Copyright © 2006 John Wiley & Sons, Ltd.