Geomorphological evidences of paleosurge activity in Lake Viedma Lobe, Patagonia, Argentina

Abstract

The valley of Lake Viedma represents one of the main ice flow axes during the Quaternary glaciations of Patagonia. Geomorphological mapping of the eastern sector of the lake, between the shoreline and the end moraine systems attributed to the Last Glaciation, allowed us to recognize a large number of ice-marginal and subglacial landforms. The landform assemblage of this area matches with previous models of surging glacier landsystems around the world. We identified the three geomorphological zones that characterise surging glacier landsystems, with some mixing of the zones, possibly related to multiple surges. The outer zone includes push moraines, thrust-block moraines, overridden moraines and hummocky moraines. In the middle zone, overridden moraines and hummocky moraines were developed. Finally, the inner zone is composed of megaflutes, crevasse-squeeze ridges, eskers and till eskers in a till plain. We interpreted these geomorphological features as evidence of surge activity of the Lake Viedma Lobe. A combination of topographic setting, soft-bedrock and the presence of a proglacial lake in contact with ice could have contributed to the development of surge activity in the Viedma paleoglacier. It could have been triggered by a change in the glacial thermal regime of the Viedma paleoglacier from polar during the Last Glacial Maximum to polythermal or temperate during the beginning of the Late Glacial.