Active layer and permafrost thickness in rock glaciers derived from geophysical methods in the semiarid Andes of Argentina

Abstract

The Argentinean Central Andes region (31°S to 35°S) exhibits one of the largest densities of rock glaciers on Earth. However, few studies have focused on the knowledge of the internal structure of these landforms. In the present paper, a characterization of the internal structure of two rock glaciers has been achieved by using Seismic Refraction Tomography and Vertical Electrical Sounding. In one of the rock glaciers, the thickness of the active layer is quite homogeneous, while in the other said thickness diminishes towards the front. In both rock glaciers, near the top of the active layer, the P-wave velocity values vary between 350 and 600 m/s, while in the bottom of the layer the P-values range from 800 to 1700 m/s. As regards the permafrost layer, it shows an irregular thickness with values varying between 4 and 27 m approximately. In addition, P-wave values ranging from 1600 to 3300 m/s and a few kΩm values of electrical resistivity have been recorded. The increase of geophysical surveys in rock glaciers in the Andes region is expected to give a better understanding of the characteristics, distribution and origin of the ice present in these landforms. It should also allow researchers to estimate with certainty their ice content as solid-state reserves.