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

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 as well as 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 weeks per year for Lecidea promiscens and 40 weeks for Rhizocarpon geographicum. Rhizocarpon geographicum prefers northerly exposed surfaces; Sporastatia testudinea seems to prefer areas with a long snow-cover duration. Growth rates for Rhizocarpon geographicum and Sporastatia testudinea are estimated to be 1 to 2 cm per 100 yr. Growth of larger thalli may be strongly inhibited.