Investigating rock moisture at a sandstone massif in the Saxonian Switzerland climbing area

Titelangaben

Sass, Oliver:
Investigating rock moisture at a sandstone massif in the Saxonian Switzerland climbing area.
In: Journal of Geomorphology. Bd. 1 (2022) Heft 1 . - S. 25-41.
ISSN 2628-6025
DOI: https://doi.org/10.1127/jgeomorphology/2022/0711

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Abstract

In the “Saxonian Switzerland” climbing area of eastern Germany, access for climbers is limited during wet conditions as damp rock may lose stability. The aim of this study is to assess the spatial distribution of rock moisture to support visitor control measures. The investigations presented here deal with the spatial distribution of dampness. This involved the testing, cross-checking and calibration of rock moisture sensors (microwaves and 2D-resistivity) in the laboratory and in the field, and assessment of rock stability using a Schmidt Hammer. The field measurements were carried out at six test sites in different topographical situations at the “Gohrisch” massif. Conversion of microwave/resistivity readings to moisture content was successful in the laboratory but difficult in the field, where many readings were outside the range of the calibration curves. Field measurements with microwave sensors and 2D-resistivity did not always agree, which can be explained by the very different measurement geometry. Laboratory tests showed that the sandstone in fact loses compressive strength when wetted. The interior of the rock was wetter than the surface in most cases. Wetness seems to derive from a pore water body inside the rock rather than from direct precipitation. The foot of the rock face was wetter than the summits of the studied massif. 2D-resistivity and Schmidt Hammer data provided evidence of surface-parallel zones of weakness at all sites that are exposed to solar radiation which was attributed to thermal weathering processes. Stronger temperature and moisture fluctuations in the summit area appear to favour surface weathering by granular disintegration.