Internal structure of two alpine rockglaciers investigated by quasi-3D electrical resistivity imaging (ERI)
Adrian Emmert and Christof Kneisel
Institute of Geography and Geology, University of Würzburg, D-97074, Germany
Received: 31 May 2016 – Accepted for review: 29 Jun 2016 – Discussion started: 04 Jul 2016
Abstract. Interactions between different formative processes are reflected in the internal structure of rockglaciers. Its detection can therefore 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 at two different rockglacier sites in the Eastern Swiss Alps by means of quasi-3D electrical resistivity imaging (ERI). This approach enables an extensive mapping of subsurface structures and hence the performance of a spatial overlay between site-specific surface und subsurface characteristics. At Nair rockglacier, we discovered a gradual descent of the frost table in a downslope direction and a homogenous decrease of ice content which follows the observed surface topography. This is attributed to ice formation by refreezing meltwater from an embedded snowbank or from a subsurface ice patch which reshapes the permafrost layer. The heterogeneous ground ice distribution at Uertsch rockglacier indicates that multiple processes on different time domains were involved in rockglacier development. Resistivity values which represent frozen conditions vary within a wide range and indicate a successive formation which includes several rockglacier advances, past glacial overrides and creep processes on the rockglacier surface. In combination with the observed rockglacier topography, quasi-3D 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 rockglaciers. Results show the value of the quasi-3D ERI approach but advice the application of complementary geophysical methods for interpreting the results.
Emmert, A. and Kneisel, C.: Internal structure of two alpine rockglaciers investigated by quasi-3D electrical resistivity imaging (ERI), The Cryosphere Discuss., doi:10.5194/tc-2016-135, in review, 2016.