Investigations regarding Alpine talus slopes using ground‐penetrating radar (GPR) in the Bavarian Alps, Germany

Abstract

AbstractThe applicability of ground‐penetrating radar (GPR) for the investigation of loose debris was tested at two sites (Viererkar and Zugspitzplatt). A pulseEKKO 100 GPR system equipped with 25 MHz antennae was utilized. The aim of the investigation was to record the base of the debris layer, and thereby acquire an estimation of the backweathering rates of the adjacent rockwalls. The study areas are situated in the Northern Alps near the German–Austrian border. The sites are characterized by steep limestone rockwalls and extensive talus accumulations. A total of six profiles was surveyed.The method is suitable and effective for a quick survey in this dry, high‐ohmic substrate. The GPR system was able to deliver information about the subsurface stratigraphy to c. 70 m depth. The boundary line to the bedrock was discovered – depending upon the profile surveyed −5 to 25 m below the surface. The base of the debris material sometimes shows no distinct reflection. Buried features (V‐shaped furrows, zones overdeepened by ice action, geological structures) could be detected. Arched structures well below the talus–bedrock interface can be interpreted as drainage systems in the karstic bedrock. A thick scree layer of Late Glacial age was separated from a thinner layer on the talus surface, which was related to the Holocene.The backweathering rates were fixed by a calculation of talus volume to c. 100 mm/103 a during the Holocene (Viererkar) and 150–300 mm/103 a (Zugspitzplatt). The detrital formation in north‐exposed sites is twice as intense as in south‐exposed sites. These results match the rates of recent rockfall in the same area of investigation. The calculated backweathering for the late glacial period is 150–730 mm/103 a.The magnitude of the calculated rockwall retreat lies well within the range of previous measurements. The discrepancy between some weathering rates highlights the fact that recent and past relief formation must be differentiated. Otherwise recent removal rates may be overestimated. Copyright © 2001 John Wiley & Sons, Ltd.