Surface Movement and Lichen-Cover Studies at the Active Rock Glacier near the Grubengletscher, Wallis, Swiss Alps

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Abstract
Geomorphological, geophysical, lichenometrical and photogrammetrical data and information are presented and discussed. The rock glacier is in an environment of discontinuous permafrost, partially cold glacier ice and groundwater in Quaternary sediments. It consists of frozen debris from the taluses at the valley walls and carries some buried massive ice on its back that mainly represents buried snowbank ice from avalanche cones. The stress field within the rock glacier must have been changed during the Neoglacial advances of the Grubengletscher at its southern margin. The interaction of permafrost and groundwater is important for the behavior of the rock glacier and for the evolution of marginal glacier lakes in similar cases. The ecological conditions for the growth of lichens at the rock-glacier surface vary extremely in space and time. Lecidea promiscens occurs most frequently and in all exposures. Rhizocarpon geographicum and Sporastatia testudinea lichens generally are very rare and even absent within the limits of the 1850 advance of the Grubengletscher. The maximum snow-cover duration that still allows lichen growth may be on the order of 46 wk/yr for L. promiscens and 40 wk for R. geographicum. R. geographicum prefers northerly exposed surfaces; S. testudinea seems to prefer areas with a long snow-cover duration. Growth rates for R. geographicum and S. testudinea are estimated to be 1-2 cm/100 yr. Growth of larger thalli may be strongly inhibited.

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