Hazard assessment investigations in connection with the formation of a lake on the tongue of the Unterer Grindelwaldgletscher, Bernese Alps, Switzerland

The surface of the Unterer Grindelwaldgletscher glacier tongue has subsided by more than 200m over the last 150 years.The tongue of Unterer Grindelwaldgletscher is covered with an uneven layer of debris.  The layer is thicker towards the terminus due to the ongoing collapse of an unstable rock face located there, with the effect that the surface lowering rates upglacier are higher than right at the terminus.  This led to the development of a topographical depression where a lake started to form in 2005.  This lake has been growing in size ever since and poses an increasing threat to the communities downstream as it can drain rapidly and cause floods.  To make a hazard assessment of the situation, we looked at the future development of the glacier tongue and estimated future lake volumes.  With these estimates we calculated the expected peak discharges and advance warning times of such floods.  These calculations were done with a model of glacial outburst floods.  The goal of the study was to determine the damage potential to Grindelwald and communities further downstream, and to evaluate possible preventative measures.
This work was done in collaboration with Dr. Hansruedi Keusen (GEOTEST AG).