Introduction

Vertical electrical resistivity soundings (VES) have been extensively used to investigate the internal structure of rock glaciers (e.g. Fisch et al. 1977, King et al. 1987, Ikeda and Matsuoka 2002). In particular, two-dimensional (2D) electrical resistivity tomography (ERT) has recently revealed the internal structure in greater detail (e.g. Vonder Mühll et al. 2000, Ishikawa et al. 2001, Ikeda and Matsuoka 2006, see also Chapters 1 and 6). Hauck and Vonder Mühll (2003), however, argued that even such tomographical methods include ambiguity in the model inversion and interpretation of DC resistivity. Although combining different geophysical properties reduces ambiguity in the interpretation of a single geophysical property (Haeberli 1985, Hauck and Vonder Mühll 2003), many studies have relied on DC resistivity methods alone. Thus, interpretation of DC resistivity in rock glaciers and related terrain requires further assessment.

This study compares DC resistivity with P-wave velocity in a number of rock glaciers. DC resistivities and/or P-wave velocities were measured on 26 talus-derived rock glaciers lying near the lower limit of mountain permafrost in the Upper Engadin, Swiss Alps. Both one-dimensional (1D) VES and 2D ERT surveys were performed at seven sites. Special attention was given to the effects of spatial variations in lithological and thermal conditions. The results were compiled for three types of rock glaciers:

1. (i) bouldery rock glaciers having an active layer composed of matrix-free boulders,

2. (ii) pebbly rock glaciers consisting of matrix-supported pebbles and cobbles, and

3. (iii) (densely) vegetated rock glaciers that mostly represent relict (bouldery) rock glaciers (see Ikeda and Matsuoka 2002, 2006 for the classification).