Ground-penetrating radar surveys on rock glaciers in the Vanoise Massif (Northern French Alps): methodological issues

Ground-penetrating radar (GPR) coupled with surface morphology analysis was used to depict the stratigraphic features and the architecture of rock glaciers in the Vanoise Massif, northern French Alps. GPR data were collected using a PulseEKKO 100 unit with 50 MHz antennas, then processed and interpreted. Two longitudinal GPR profiles acquired on the Planette and Sachette rock glaciers, respectively, are presented as examples. The interpretation of the GPR data is based on the differential application of several standard gain functions (constant gain, automatic gain control) on the GPR profiles in order to enhance the images and to discriminate reflection events. On the whole, the stratigraphy of the rock glaciers appears complex with prominent internal boundaries that often correlate with geomorphological surface boundaries. The architecture of the Planette and Sachette rock glaciers is therefore multi-unit, which calls into question their sequential way of deposition.