InSitu Site Investigation Geomorphology Geology

The analysis of the geomorphological features at a given site provides a preliminary diagnosis of whether permafrost is present or not. In addition to the analysis of topographical maps and aerial photographs, in-situ site investigations are carried out to identify potential permafrost-related features, prior to more complicated and costly geophysical and geotechnical investigations. The use and relevance of geomorphological analyses is unfortunately often underestimated, although the method is a low-cost and simple one. A solid understanding of alpine morphology is nevertheless required for the successful interpretation of the features observed and therefore expert knowledge is to be sought.

Various geomorphological features and processes can be discerned; as a result, ranges of ice contents may be estimated and an overview of the occurrence and potential for permafrost related processes such as erosion or mass movements may be established. Whereas permafrost terrain at high latitudes is characterised by a large number of clearly recognisable features, it is more difficult to determine the presence of high altitude permafrost on the basis of morphology alone - as is reflected in books on the periglacial environment, where only a few pages are dedicated to mountain permafrost, as it is often primarily associated with rock glaciers (e.g. French, 2007).

Other features that are commonly found in mountain permafrost regions, and can be of assistance in the diagnosis of permafrost (Fig. 8), include ice-rich moraines (Fig. 9), perennial snow patches (Fig. 10), creeping scree slopes and thermokarst depressions (Fig. 11). Rock glaciers (Fig. 12) are the most reliable diagnostic feature and can be used to indicate the lower altitudinal limit of discontinuous permafrost. Active rock glaciers contain ice and creep downslope - they are characterised by having steep flanks and snouts (>38°) as well as a bulging shape, with transverse ridges and hollows. Little vegetation (Fig. 13) or lichens grow at the surface. Springs at the snout are generally colder than 3°C.

Figure 9. Ice-rich lateral moraine, Morteratsch glacier, eastern Swiss Alps. Ice is visible in the scars (M.

Phillips).

Figure 9. Ice-rich lateral moraine, Morteratsch glacier, eastern Swiss Alps. Ice is visible in the scars (M.

Phillips).

Figure 10. Perennial snow patches (avalanche debris) at 2800 m asl above Pontresina in the eastern Swiss Alps (M. Phillips).
Figure 11. Recently formed and rapidly growing thermokarst depression on a ski run at 2600 m asl in the western Swiss Alps (Depth of hole: 3 m, Summer 2007, M. Phillips).
Figure 13. Stunted trees (80-150 years old) on a low-altitude permafrost scree slope in the Swiss Jura (M. Phillips).

Ice-rich moraines are generally found in recently deglaciated terrain. High ice contents can cause them to be very steep (>38°). Ice can be visible in fresh scars on the steep flanks and creep-induced features such as gelifluction lobes can occur (Fig. 8). Scree slopes are one of the most frequently occurring features in alpine environments - sometimes creep-induced features can be visible, which may however be due to solifluction. Ice is very rarely visible -and only seen in fresh scars (e.g. due to stream erosion at the base of a slope). Any vegetation on alpine permafrost is azonal or stunted, helping to distinguish the features from non-permafrost ones. Perennial snow patches are present for long periods of the summer on a regular basis and simply indicate that the underlying ground temperature is at 0°C or colder. They often consist of avalanche debris at the base of steep slopes or of windblown snow in hollows. Thermokarst depressions and slumps etc. can occur in any kind of frozen ground and are an indicator of permafrost degradation. Thaw subsidence due to the melting of ground ice leads to the formation of fresh depressions that often grow rapidly, in the course of one summer. Although rock walls look similar in any type of terrain, fresh rock fall scars containing ice can sometimes be seen in permanently frozen rock walls.

The geological site investigation gives a first indication of the composition, structure, stability and potential ice/water content of the ground. In addition to the standard geological observations, it is important to be able to establish the duration and type of the last glaciation at the site - which has an influence on ground temperature. The thickness and origin of ground surface material should be determined, and water/ice contents estimated. In order to establish a detailed stratigraphy and identify the type of ice (e.g. segregated ice lenses, massive ice layers, ice in cracks or covered ice), drilling is necessary. Geophysical measurements can deliver information on the layering of the ground and the location of ice over a large surface area but does not provide detailed geological and geotechnical information. Potential instabilities, the mass of creeping bodies and the mechanisms of erosion in the vicinity of the construction site should be identified in the geological analysis. Geological maps and field investigations also allow the presence of aquicludes to be determined - this helps to forecast where water and ice may accumulate due to construction activity or to the presence of an infrastructure. Ultimately, the geological report should state prohibited and recommended anchor directions.

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