Abstract:
The prediction of the time of breaking off of instable ice or rock masses can be important if settlements or other fixed features (roads, railway etc.) exist within the potential hazard zones. Two such events happened recently in Switzerland. The first one was an icefall from a hanging glacier situated on the west-facing slope of Eiger (Bernese Alps). A large icefall has the potential to impinge on tourist facilities located in the immediate vicinity of the Jungfraujoch-railway station Eigergletscher. The second case concerns a rock destabilisation which occurred from a rock wall in the vicinity of Jungfraujoch. This instable rock mass threatened the exit of a tunnel used by tourists leaving the Jungfraujoch railway station. In both cases, movement surveys were undertaken soon after the first signs of a destabilisation. An almost perfect regularity by which such instable masses accelerate prior to the time of breaking off could be recognised. The time of breaking off can be predicted quite accurately by extrapolation of the deformation-time function, which has been approximated by a hyperbolae.