Composition, flow and development of two tongue-shaped rock glaciers in the permafrost of Svalbard

Svalbard is in the zone of continuous permafrost with depths varying betwee n 200 and 450 m in the interior. Two tongue-shaped rock glaciers on Svalbar d have been investigated. The results of surface velocity measurements reve al horizontal surface velocities of 0.05-0.10 m a(-1). The oldest surface o f these rock glaciers is roughly estimated to be 4000 years, based on a ten tative dating by calculation of the length/surface-velocity ratio (LSVR). W ith respect to rock glacier dynamics and long-term initial development of t heir particular forms, it is likely that the rock glaciers started to devel op at the onset of the Holocene. DC resistivity results indicate an inner s tructure with a 20-35 m thick high-resistivity ice-rich layer (100-900 k Om ega m) lying on a lower resistive layer (5-70 k Omega m) interpreted as ice -saturated sediments. Ground penetrating radar (f = 50 MHz) shows clear ref lection horizons or layers along the longitudinal profile of the rock glaci er. In a short zone at the rear of the profile, the layers are oriented par allel or slanting downwards in relation to the rock glacier surface. In the frontal part the layers slant upwards. The orientation of the layers chang es in a narrow transition zone. The layers can be recognized clearly down t o 15-20 m depth. They are interpreted to represent sediments supersaturated with ice alternating with layers of rockslide debris. The supersaturated l ayers are interpreted as snowdrifts later covered with debris from rockslid es. Repeated mass movement events result in aggradational ice layers gradua lly becoming part of the creeping rock glacier. This mechanism is assumed t o be the most important accumulation process for the development of the inv estigated rock glaciers. Copyright (C) 2000 John Wiley Br Sons, Ltd.