Gruben glacier and rock glacier, Wallis, Switzerland: glacier ice exposures and their interpretation

ABSTRACT Field observations, map analysis and the use of terrestrial and aerial photography and Google Earth show that the Gruben rock glacier, discussed in the literature since 1974, does contain a glacier ice core. Mapped as bare glacier ice at the time of the first map, about AD 1850, subsequent cover by debris from the surrounding cliffs has preserved what is now a slow-moving glacier core beneath a debris cover about 0.5 m thick. Formerly, the steeper and thicker glacier moved debris to the snout much more rapidly than at the present flow rates. The, adjacent, and once co-flowing, tongue of glacier ice was sparsely covered and has down-wasted substantially since the Little Ice Age (ca AD 1850) maximum. Surface down-wasting, surface lakes, ice exposures, and snout recession indicate that the rock glacier’s volume is reducing by wastage of the glacier ice core. This reduction in thickness and surface slope over the last 150 years is sufficient to explain all the observed phenomena in the Gruben basin and present-day low (<1 ma−1) rock glacier surface velocities. Further exposures of glacier ice in the rock glacier are expected with increasing ‘climatic warming’. These findings suggest that the ‘permafrost’ origin of rock glaciers should be re-evaluated.