Proglacial lake-ice conveyors: A new mechanism for deposition of drift in polar environments

Interpretation of sediments in the floors of valleys opening into western McMurdo Sound has been so problematic that it has hindered understanding of the late Quaternary history of the,Antarctic Ice Sheet. Lateral moraines and enclosed drift sheets so clearly exposed on the headlands are generally absent within the valleys themselves. Instead, valley-floor sediments and landforms consist of hummocky, stratified fine sediment generally capped by coarser, poorly sorted material, small cross-valley and longitudinal ridges, and lateral ridges that superficially resemble shorelines. One clue as to the origin of these deposits is that at least some of the valleys were occupied by large proglacial lakes during the last glacial maximum (e.g. Glacial Lakes Trow-bridge and Washburn in Miers and Taylor Valleys, respectively). This paper describes a new mechanism observed in a modem perennially ice-covered proglacial lake that documents the movement of glacial debris beyond the grounding line across the surface of the lake. This mechanism accounts for the absence of moraines and other ice-contact features on the valley floors, as well as for the presence of the other deposits and landforms mentioned above.