Prospecting on the electric rock glaciers cirque Sainte-Anne (Queyras, Alpes du Sud, France)

The Sainte-Anne cirque in the Queyras area contains several active rock glaciers. The internal structure of the main two (Ste-Anne and Petite-Part) have been studied by electrical means (about 15 resistivity soundings of the Schlumberger type). The apparatus and the methodology have been tested in the Alps since 1986. The shape of the resistivity curves clearly shows the occurrence of ice in the ground. The interpretation of these curves leads us to estimate the ice content and geometry of the investigated layers. In the Sainte-Anne area, the internal structure of the rock glaciers is somewhat complex, with coexistence of rather pure ice from the upper glacierets and ice-cemented sediments of periglacial origin. The tongue of the rock glacier can be iceless (Sainte-Anne). The active terminal lobe always contains a core of poorly ice-cemented sediments. This is responsible for the measured movements (35 cm/a) and the observed ridges. This core, actually melting, is about 20 m thick at Sainte-Anne and 10 m at Petite-Part, under a few metres of ice-free sediments.