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Channel-amphitheatre landforms resulting from liquefaction flowslides during rapid drawdown of glacial Lake Fraser, British Columbia, Canada

August 12, 2021

Unusual channel-amphitheatre landforms are present in Late Pleistocene–early Holocene, subaqueous fan and delta deposits in the glacial Lake Fraser basin, central British Columbia. The lake formed during the decay of the last Cordilleran Ice Sheet and drained ~11,500 years ago during a large outburst flood. The fronts of a delta and two subaqueous fans consisting of silt to fine sand are marked by branching networks of wide, nearly flat channels that terminate upstream in digitate, steep-walled amphitheatres. We propose that these channel-amphitheatre landforms formed by liquefaction flowslides that were induced by the rapid drawdown of glacial Lake Fraser during the outburst flood. Similar geomorphic forms, which we believe also to be associated with rapid drawdowns of large Late Pleistocene–early Holocene lakes, occur elsewhere in North America. A recent tailings dam failure and an intentional breaching of a 100-year-old hydroelectric dam provide insights into the processes responsible for the landforms. By using geomechanical analysis, we show how rapid lake drawdown can trigger liquefaction flowslides in deposits of silt to fine sand. The novelty of our approach lies in combining geomechanical reasoning with geomorphic analogues to understand histories of ancient glacier-dammed lakes and of the glacial lake outburst floods that are sourced from them.

Citation Information

Publication Year 2021
Title Channel-amphitheatre landforms resulting from liquefaction flowslides during rapid drawdown of glacial Lake Fraser, British Columbia, Canada
DOI 10.1016/j.geomorph.2021.107898
Authors Brendan G.N. Miller, Richard M. Iverson, John J. Clague, Marten Geertsema, Nicholas J. Roberts
Publication Type Article
Publication Subtype Journal Article
Series Title Geomorphology
Series Number
Index ID 70226896
Record Source USGS Publications Warehouse
USGS Organization Volcano Science Center

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