Rhombohedral crevasse-fill ridges at the marine margin of a surging Svalbard ice cap

Abstract

The ice cap of Austfonna in eastern Svalbard is the largest in the Eurasian Arctic at 8000 km2 and has about 200 km of marine-terminating ice cliffs (Dowdeswell et al. 2008). Several of its drainage basins are of surge type (Meier & Post 1969) and, between 1936 and 1938, one of these basins (Brasvellbreen; 1100 km2) increased its velocity rapidly and underwent an advance of about 20 km along a 30 km wide front (Schytt 1969). Since that time the ice-cap terminus has stagnated and retreated, losing mass by a combination of surface melting, thinning and iceberg production. Retreat has revealed several distinctive and well-preserved submarine landforms (Fig. 1) linked to this recent surge activity (Solheim & Pfirman 1985; Solheim 1991). Fig. 1. ( a ) Rhombohedral ridges and a terminal moraine ridge on the seafloor offshore of Brasvellbreen, an outlet of the Austfonna ice cap in eastern Svalbard. Image courtesy of the Norwegian Hydrographic Service (Permission no. 14/G754). Acquisition system Kongsberg EM1002. Frequency 97 kHz. Grid-cell size 3 m. The ridges are interpreted to have been formed by the filling of basal crevasses with deforming diamictic sediment. ( b ) Oblique aerial photograph of the surge and rapid advance of Brasvellbreen in 1938 (Photo S38-1958; courtesy of Norsk Polarinstitutt). ( c ) Location of study area (red box; map from IBCAO v. 3.0). ( d …