Geomorphic and sedimentary signatures of catastrophic glacier detachments: A first assessment from Flat Creek, Alaska

Large-volume detachments of low-angle mountain glaciers involve the sudden mobilization of large amounts of glacier ice and lithic material in long-runout mass flows. Scientific investigations of these events have only recently brought to light their global occurrence and the similarities in the conditions under which they occur. While this recent research suggests that glacier detachments may become more frequent in a warming climate, a long-term record is largely lacking. Knowledge of the geomorphic signatures of glacier detachments could help establish such a record. Here, we present the first geomorphic and sedimentary assessment of a glacier detachment deposit. We investigate the landscape impacts of the Flat Creek glacier detachments in Alaska’s St. Elias mountains through a combination of remote sensing analyses, field observations, Electrical Resistivity Tomography, and grain size and grain orientation analyses. From these data, we outline a land-system model that may help identify past glacier detachments elsewhere. Some of the most distinguishing features we documented were large bodies of buried ice-conglomerates, a rapid response of the remnant glacier ice, clusters of small-scale thermokarst ponds, countless molards, parallel striations etched into the hillslope and individual clasts, and a very long runout distance. We assess these features in terms of their longevity in the landscape and compare them to what has been described at glacier detachment sites elsewhere. Finally, we discuss to what extent glacier detachment deposits can be distinguished from deposits left by rock(− ice) avalanches, debris flows, and surging glaciers, and show that a differentiation is possible if detailed field investigations are undertaken.