Mapping crevasse-squeeze ridges- defining characteristics for improved understanding and identification of these landforms

Crevasse squeeze ridges (CSRs) are landforms indicative of glacier surging and ice stream shut down. They form during fast ice flow, when high basal water pressures and extensional ice flow cause hydrofracturing in the base of the glacier and subsequent squeezing/injection of sediment into basal crevasses. When the fast ice flow phase ends, ice stagnates and down wasting of the ice surface occurs. If lateral support is maintained the sediment ridges are preserved as the glacier passively retreats. Geometries of these ridge networks can thus provide insights into subglacial conditions during phases of fast ice flow. This is important because the rapid movement of ice from areas of accumulation to ablation zones, during fast ice flow phases, exposes a greater area of ice to melting having long term impacts on the mass balance of these glaciers.

CSR characteristics have been inconsistently reported in the literature and in some cases have been misidentified. Here we present the first global dataset combining CSR information mined from the literature with new mapping and use this to define CSR characteristics in both surging and ice stream contexts as well as in terrestrial and marine settings. Using ArcGIS Pro, we map ridges from high resolution aerial imagery and digital elevation models, and extract metrics on ridge lengths, network density, and orientations in relation to ice flow direction. CSRs have been mapped at modern surge-type glaciers in Iceland and Svalbard, and in palaeo-landscapes in central Canada, the British Isles, and Northern Europe related to ice stream shutdown. Furthermore, we categorise the data into marine and terrestrial environments because CSRs are often better preserved in marine settings, due to the action of subaerial and meltwater erosional processes occurring on land.

This new dataset provides a representative understanding of CSR morphologies to allow better identification of the landform in the future, which will help to understand subglacial processes beneath fast-flowing ice masses. Understanding basal conditions in any glacial system is challenging due to the difficulties of acquiring direct measurements at the base of the glacier. CSRs represent these basal conditions and can therefore provide insights.