Abstract
Abstract. Permafrost distribution in rock walls surrounding receding glaciers is an important factor in rock stability and rock wall retreat. We investigated bedrock permafrost distribution in the Dachstein Massif, Austria, reaching up to 2995 m a.s.l. The occurrence, thickness and thermal regime of permafrost at this partly glaciated mountain massif are scarcely known. We applied a multi-method approach with continuous ground surface and near-surface temperature monitoring (GST), measurement of the bottom temperature of the winter snow cover (BTS), electrical resistivity tomography (ERT), airborne photogrammetry, topographic maps, visual observations, and field mapping. Our research focused on several steep rock walls consisting of massive limestone above receding glaciers exposed to different slope aspects at elevations between ca. 2600 and 2700 m a.s.l. We aimed to quantify the distribution and conditions of bedrock permafrost particularly at the transition zone between the present glacier surface and the adjacent rock walls. According to our ground temperature data, permafrost is mainly found at north-facing rock walls. At south-east-facing rock walls, permafrost is probable only in very favourable cold conditions at radiation-sheltered higher elevations (>2700 m a.s.l.). ERT measurements reveal high resistivities (>30 000 Ω m) at ≥1.5 m depth at north-exposed slopes (highest values >100 kΩ m). Deducted from laboratory studies and additional small-scale ERT measurements, these values indicate permafrost existence. Permafrost bodies were found at several rock walls independent of investigated slope orientation; however, particularly large permafrost bodies were found at north-exposed sites. Furthermore, at vertical survey lines, a pronounced imprint of the former Little Ice Age (LIA) ice margin was detected. Resistivities above and below the LIA line are markedly different. At the LIA glacier surface, the highest resistivities and lowest active-layer thicknesses were observed. The active-layer thickness increases downslope from this zone. Permafrost below the LIA line could be due to permafrost aggradation or degradation; however, the spatial patterns of frozen rock point to permafrost aggradation following glacier surface lowering or retreat. This finding is significant for permafrost and cirque erosion studies in terms of frost-influence weathering in similar high-mountain settings.
Highlights
Climate change has a great impact on perennially frozen and glaciated high-mountain regions (Haeberli and Hoelzle, 1995; Haeberli et al, 1997; Harris et al, 2001; Lieb et al, 2012)
Our research focused on the lower parts of steep rock walls of recently deglaciated areas at four different measurement sites (MSs) at elevations between 2600 and 2700 m a.s.l. next to the Schladming and Hallstatt glaciers (Fig. 1)
For MSG (Fig. 5d) the results show some more fluctuation in temperature at the beginning of the year, probably because of less insulation due to a shallow snowpack
Summary
Climate change has a great impact on perennially frozen and glaciated high-mountain regions (Haeberli and Hoelzle, 1995; Haeberli et al, 1997; Harris et al, 2001; Lieb et al, 2012). Glaciers might be separated from the adjacent headwall by a distinct gap or crevasse (randkluft). Such crevasses are typical glacial features in our study area. Air can enter into this crevasse allowing for a better coupling of the air and bedrock even below the glacier surfaces and more efficient cooling during the summer season (Sanders et al, 2012). Both a polythermal glacier and a glacier with a distinct randkluft might allow for permafrost aggregation below the glacier surface
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