SHALLOW CORE DRILLING AND BORE-HOLE MEASUREMENTS IN THE PERMAFROST OF AN ACTIVE ROCK GLACIER NEAR THE GRUBENGLETSCHER, WALLIS, SWISS ALPS

On this active rock glacier is shallow core drilling to a depth of 700 cm and geophysical bore-hole investigation was carried out to collect data about the rock-glacier permafrost and to gain experience for future deep drilling. The interpretation of a set of radiaoctive bore-hole logs (gamma, neutron-neutron, and gamma-gamma) run in the hole immediately after drilling shows that the ice content of the frozen sediments is c90% by volume at the permafrost table and probably asymptotically reaches an average value some meters below (508-70%). Besides air temperature (altitude) and solar radiation (exposure), snowcover thickness during winter seems to be the main factor influencing the ground temperatures. Based on geothermal calculations and estimations it is suggested that the rock-glacier permafrost is not in equilibrium with the present-day surface temperature but with a surface temperature from the 'Little Ice Age' which was some 0.5-1..0oC colder. The results presented here confirm that alpine rock glaciers are creep phenomena in discontinuous permafrost.-from Authors