Hazard assessment investigations due to recent changes in Triftgletscher, Bernese Alps, Switzerland
- 1Laboratory of Hydraulics, Hydrology and Glaciology (VAW), ETH Zürich, C8092 Zürich, Switzerland
- 2Chemnitzer Werkstoffmechanik GmbH, Otto-Schmerbach-Str. 19, 09117 Chemnitz, Germany
- 3WSL Institut for Snow and Avalanche Research (SLF), 7260 Davos Dorf, Switzerland
- 4Institute of Low Temperature Science, Hokkaido University, Kita-19 Nishi-8, Sapporo, 060-0819 Japan
- †deceased, July 2004
Abstract. The details and the consequences of the recent retreat of Triftgletscher (Gadmertal, Bernese Alps, Switzerland) have been investigated. Geodetic volume changes indicate a strong decrease since 1929 while the position of the terminus remained practically unchanged until 1990. The role played by calving in the tongue retreat running from 2000 to 2006 is confirmed by means of a mass balance model including a calving criterion. Results show that without calving, it would have taken two years longer for the lake to form than has been observed. The consequences of the ensuing tongue destabilization are surveyed, first with an ice avalanche model and second with a hydraulic study of the potential impulse wave triggered by the impact of the falling ice mass in the lake. Results point out that ice avalanches with volumes greater that 1 × 106 m3 will flow into the lake and that in the worst scenario, a discharge of 400 m3 s−1 is expected to reach the endangered area in Gadmertal 11 min after the break-off. In order to detect surface motion precursors to such ice avalanches, a photographic monitoring system was installed. The results indicate seasonal variations with peak velocity in summer and no significant change during the other months. Spectacular velocity increases were not observed so far.