Sea-floor morphology outside a grounded, surging glacier; Bråsvellbreen, Svalbard

Acoustical profiling and bottom photography reveal several different sea-floor morphological features adjacent to the grounded Bråsvellbreen glacier on Svalbard, northwestern Barents Sea. Some of the features and their distribution may be closely related to a major glacial surge in 1936-1938, and as such are valuable in identifying former surges in other locations. A continuous, wide ridge with a characteristic asymmetrical cross-section, running subparallel to the glacier, is the end moraine defining the maximum extent of the surge. A large part of the material forming this ridge is most likely rapidly deposited from meltwater during the surge. A rhombohedral pattern of smaller mounds inside the ridge is probably an expression of relief in the glacier sole during the surge. Discontinuous arcuate ridges define local, minor oscillations during retreat of the ice at a later stage. Iceberg plough marks are most frequent seaward of the end moraine, their orientation is controlled by the combination of a coastal current, offshore katabatic winds and topography. Superimposed on plough marks are secondary features such as a "washboard pattern" and striae, most likely caused by push-up of overconsolidated material during gouging and multi-keel icebergs, respectively. Bottom sediments, observed in photographs and cores, are loose, pebbly muds with high variability in clast content, resting on overconsolidated material, probably basal till. Mud deposition presently prevails close to the glacier.