Glacial outburst flood sediments within Disenchantment Bay, Alaska: Implications of recognizing marine jökulhlaup deposits in the stratigraphic record

Glacial outburst floods have been observed or inferred in most glaciated regions of the world. Outburst flooding events along past ice-sheet margins have been discussed as possible causes for changes in ocean circulation while subglacial lake drainage under ice sheets may influence ice-sheet stability. The recognition of these geologically instantaneous events in the marine sediment or rock record is critical in order to characterize the magnitude and frequency of past outburst events as well as to predict the likelihood of future occurrences. In this paper, we characterize outburst lithofacies and infer depositional processes from two outburst floods within Disenchantment Bay, Alaska, and compare these deposits to other recognized outburst deposits within marine depositional settings. Here we show that the outburst deposits are lithologically similar and are composed of stratified mud, sand, and diamicton. We interpret these facies to have been formed by sediment gravity flows and hypopycnal plume sedimentation. These results show that the volume of sediment, lithofacies, and inferred depositional processes cannot be easily distinguished from normal sediment accumulation within the proximal temperate glacimarine depositional environment. The paucity of fluvial subglacial discharge in polar glacimarine environments suggests the potential for recognition of such deposits in the Antarctic.

Research highlights
► We delineate the 1986 and 2002 outburst sediments within Disenchantment Bay, Alaska.
► Despite differences in peak discharge, depositional processes are similar.
► Outburst sediments include laminated mud, sand, and diamicton.
► Deposition occurs from sediment gravity flows and hypopycnal plumes.
► Sedimentary volumes are similar to marine Icelandic jökulhlaup deposits.