Articles | Volume 11, issue 2
Research article
30 Mar 2017
Research article |  | 30 Mar 2017

Internal structure of two alpine rock glaciers investigated by quasi-3-D electrical resistivity imaging

Adrian Emmert and Christof Kneisel

Abstract. Interactions between different formative processes are reflected in the internal structure of rock glaciers. Therefore, the detection of subsurface conditions can help to enhance our understanding of landform development. For an assessment of subsurface conditions, we present an analysis of the spatial variability of active layer thickness, ground ice content and frost table topography for two different rock glaciers in the Eastern Swiss Alps by means of quasi-3-D electrical resistivity imaging (ERI). This approach enables an extensive mapping of subsurface structures and a spatial overlay between site-specific surface and subsurface characteristics. At Nair rock glacier, we discovered a gradual descent of the frost table in a downslope direction and a constant decrease of ice content which follows the observed surface topography. This is attributed to ice formation by refreezing meltwater from an embedded snow bank or from a subsurface ice patch which reshapes the permafrost layer. The heterogeneous ground ice distribution at Uertsch rock glacier indicates that multiple processes on different time domains were involved in the development. Resistivity values which represent frozen conditions vary within a wide range and indicate a successive formation which includes several advances, past glacial overrides and creep processes on the rock glacier surface. In combination with the observed topography, quasi-3-D ERI enables us to delimit areas of extensive and compressive flow in close proximity. Excellent data quality was provided by a good coupling of electrodes to the ground in the pebbly material of the investigated rock glaciers. Results show the value of the quasi-3-D ERI approach but advise the application of complementary geophysical methods for interpreting the results.

Short summary
We investigated the internal structure of two alpine rock glaciers to derive information on their development. Through a 3-D mapping of the electrical resistivity distribution of the subsurface, we could detect variations of ice content and delimit frozen and unfrozen structures. Our study shows that the development of the investigated rock glaciers is influenced by not only creep processes and remnant ice from past glaciations but also recently buried ice patches and refreezing meltwater.