Sediment release and storage in early deglaciated areas: Towards an application of the exhaustion model from the case of Massif des Écrins (French Alps) since the Little Ice Age

Abstract

Deglaciation in high mountain areas triggers a series of adjustments affecting the various geomorphic components of formerly glaciated catchments. Active processes, part of the ‘paraglacial’ open system, release and transport sediments from formerly glacierized sources to catchment sinks. Such cascade sedimentary systems may be disrupted by temporary sediments traps. To evaluate the consequences of such traps on sediment export, several test areas were selected, where former glacial geometries and glacial retreat chronology were reconstructed from field data. Special attention is given to the link between the glacial margins and the glacio-fluvial systems. During glacial retreat, the presence of morainic ridges may temporarily interrupt the sedimentary cascade system, thus forcing local aggradation and change in the glacio-fluvial pattern. The volume of trapped sediments is controlled by the volume and the position of morainic ridges, while the storage residence time is strongly dependent upon the rate of moraine erosion. The ice surface elevation and its lowering control ice-contact storages, as well as sedimentary and water fluxes. The time lag between the rate of sediment accumulation on the valley floor and the rate of glacial shrinking influences the pattern and behaviour of drainage many decades after the peak in glacial melting.