Geophysical investigation of a relict talus slope in the Bavarian Alps, Germany

摘要

In the Bavarian Alps a grass-covered talus slope was investigated using different geophysical methods to gain an insight into its structure and thickness. The talus lies at an elevation of 1,500-1,700 m within a closed cirque basin surrounded by rocky dolostone slopes. Several georadar (GPR) profiles were measured using 25 and 50 MHz antennae. Furthermore, 2D-resistivity and seismic refraction were applied and drillings were carried out in order to verify the geophysical results. The results show a good coincidence of the different methods; GPR and 2D-resistivity complement one another. The geophysical results were successfully verified by the drilling results. The talus deposits were clearly delimited from the silty and clayey cirque floor sediments. At the foot of the slope the talus debris is interlocked with lake sediments which points to episodic mudflow activity. It was difficult to delimit the actual talus base. However, the combination of the geophysical results points to further late-glacial or even older sediment layers under the Holocene talus body. The GPR method delivered additional information on the internal talus structure. According to the combined results, the uppermost 5-10 in of the talus is built up of relatively loose, fluvially redistributed talus debris related to the Holocene. A holocene back-weathering rate of 400 mm/ka can be derived from the sediment volume, which is well above the recent weathering rates derived from rockfall measurements.