The geomorphology and sedimentology of the 'Tempanos' moraine at Laguna San Refael, Chile

Abstract

The San Rafael Glacier is one of the largest and most dynamic outlet glaciers of the North Patagonian Icefield, Chile. The contemporary glacier calves into a large tidal laguna, which is partially impounded by a large arcuate moraine. This moraine, termed the Témpanos moraine, marks the former extent of an expanded San Rafael Glacier and is of an unknown age. Here we describe the geomorphology and sedimentology of the Témpanos moraine and relate these to styles of glacier advance and recession. The Témpanos moraine attains a maximum height in excess of 40 m and is either single-crested with a gentle ice-proximal face and steep distal face, or consists of multiple crests superimposed on a gentle slope. The internal composition of the moraine is variable, comprising diamicton, sorted sedimentary facies (silts, sands and gravel) and laminites. We interpret these sediments as evidence that the San Rafael Glacier advanced over a former proglacial area, culminating in the formation of the Témpanos moraine. This advance deformed a carpet of lacustrine or marine mud, which was eroded from its original location, transported and smeared over the glacier bed as a subglacial deposit. We use these sedimentary descriptions as the basis for a reconstruction of the Holocene fluctuations of the glacier.