Gravimetrical investigation of ice‐rich permafrost within the rock glacier Murtèl‐Corvatsch (upper Engadin, swiss alps)

A gravimetrical study was carried out in the area of the Murtèl‐Corvatsch rock glacier in order to check the applicability of this method in alpine permafrost. The residual anomaly observed after removal of the linear regional trend is up to −1.5 mgal. Cores of borehole 2/1987 through this rock glacier showed a very high ice content in the uppermost 30 m. Borehole geophysical measurements furnished the density distribution with depth at the drill site showing values of less than 1000 kg m −3 . According to the core stratigraphy and the density log at the drill site four layers were distinguished: an active layer to 3 m depth; massive ice (3–20 m); an ice‐silt‐sand layer (20–30 m); and a layer with ice‐saturated blocks (30–50 m). The extension of the four distinguished layers is modelled in three dimensions for the entire rock glacier according to the gravity data. The bedrock underneath the creeping permafrost is bowl‐shaped.