1 BACKGROUND AND CONCEPT
The formation and preservation of ground ice over the typical time scales (millennia) involved with the steady flow over long time intervals of large and well-developed rock glaciers require the existence of peren-nially negative ground temperatures, i.e., permafrost by definition (Haeberli, 2001)....
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.468.372 http://research.iarc.uaf.edu/NICOP/DVD/ICOP 2003 Permafrost/Pdf/Chapter_062.pdf |
| Summary: | The formation and preservation of ground ice over the typical time scales (millennia) involved with the steady flow over long time intervals of large and well-developed rock glaciers require the existence of peren-nially negative ground temperatures, i.e., permafrost by definition (Haeberli, 2001). This climatically deter-mined ground thermal condition makes rock glaciers interesting in view of quantitative paleoclimatic recon-structions (Frauenfelder et al., 2001). Moreover, the debris accumulated in rock glaciers reflects centuries and millennia of past frost weathering and rock-fall activity (Barsch, 1977; Olyphant, 1987). In order to decipher the corresponding information, rock glaciers must be dated. The following briefly outlines a strategy which com-bines a variety of applicable methods. It uses a basic concept of permafrost creep, which relates to results from extensive drilling, borehole observation, geo-physical soundings, photogrammetric analyses, perma-frost mapping etc., at Murtèl rock glacier (Figure 1; Haeberli et al., 1998). The initial condition is a talus cone with characteristic vertical sorting of grain sizes. Frost heave and creep of the ice-supersaturated finer material originally deposited on the upper part of the talus cone then forms a bulge (protalus rampart) which steadily develops into a larger rock glacier. Coarse blocks continue to accumulate at the base of the talus cone and are carried along on the back of the further advancing rock glacier until reaching its front. There, they fall down the oversteepened scree of re-exposed and thawed fine material. These coarse blocks from the rock-glacier surface are subsequently overriden by the creeping ice-super-saturated fine material. In contrast to the latter with ages increasing along flow paths, they form a stiff basal layer in which age decreases towards the rock glacier-front. The age distribution at depth in rock-glacier permafrost, therefore, is likely to contain sharp time inversions. |
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