Hazard assessment investigations due to recent changes in Triftgletscher, Bernese Alps, Switzerland

Abstract

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 ·10 6 m 3 will flow into the lake and that in the worst scenario, a discharge of 400 m 3 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.

Avalanching glacier instabilities: Review on processes and early warning perspectives

“…The glacier has experienced a rapid retreat during the last 20 years. After the year 2000, the tongue ended in steep terrain (about 35°) and its stability was questionable [ Dalban Canassy et al , ]. In the following summers, surface velocities increased from 1 to 4 md −1 , similar to those observed at the Allalingletscher (Figure ).…”

Acceleration and flotation of a glacier terminus during formation of a proglacial lake in Rhonegletscher, Switzerland

“…Given this topographic transition, longitudinal stress was expected to be exerted from the steeply inclined upper region to the terminus, and such longitudinal stress coupling might have played a key role in the ice dynamics at C2 (e.g. Kamb and Echelmeyer, 1986;Cuffey and Paterson, 2010). A bedrock bump exists beneath site C2, and the bed slopes toward the up-glacier direction in the lower reaches from C2 downward (Fig.…”

“…Motyka and others (2003) noted that simple shear ice deformation accounts for only 6% of the surface velocity observed near the terminus of Mendenhall Glacier, with the remainder being due to basal sliding. For Rhonegletscher at site C2, glacier motion due to deformation of ice was estimated as 1:4 Â 10 À4 m a À1 from the ice thickness and surface slope in 2008 and a rate factor of A ¼ 75 Â 10 À18 Pa À3 a À1 (Cuffey and Paterson, 2010). This accounts for <0.1% of the observed surface velocity.…”

Investigating the dynamics of an Alpine glacier using probabilistic icequake locations: Triftgletscher, Switzerland

“…The retreat resulted in the destabilization of the tongue, increasing its flow speed and causing frequent avalanches on both sides of the terminus [Dalban Canassy et al, 2012]. If the entire ice tongue slides into the lake or if volumes of ice avalanches exceed 10 6 m 3 , potential flood waves are a threat to the downstream Gadmertal valley [Dalban Canassy et al, 2011]. [14] The goal of the field experiments was to characterize the dynamics of the potentially unstable tongue of Triftgletscher.…”

“…The present study focuses on seismic data from Triftgletscher, Switzerland, which has been monitored since 2007 due to its steep tongue prone to break‒off [ Dalban Canassy et al , ; Dalban Canassy et al , ]. Using continuous seismic records from an on‒ice campaign network, we determine icequake hypocenters with a nonlinear probabilistic approach [ Lomax et al , ] and a three‒dimensional P wave velocity model that accounts for the complex topography of bedrock and glacier surface.…”