Influence of the connectivity with permafrost on the debris-flow triggering in high-alpine environment

Authors

  • E. Bardou Research Center on Alpine Environment, Sion, Switzerland
  • F. Favre-Bulle Research Center on Alpine Environment, Sion, Switzerland
  • P. Ornstein Research Center on Alpine Environment, Sion, Switzerland
  • J.-D. Rouiller Research Center on Alpine Environment, Sion, Switzerland

DOI:

https://doi.org/10.4408/IJEGE.2011-03.B-002

Keywords:

alpine debris flow, triggering, permafrost

Abstract

The study area is the Bonnard glacier which lies in the Anniviers Valley, Valais, Switzerland. Two glacial torrents originate from a source area that is composed of 60% of creeping permafrost which supplies loose material. Heavy rainfall events trigger debris ows on the steep slopes of the lower permafrost complex. Three scarps are visible, two of them from the last event in 2008. In scar n°1 the permafrost plays a key role in triggering debris ow by loading the streambed with unstable materials and creating an impervious layer due to the presence of ice and/or frozen ground. In scar n° 2 the triggering follows shallow landslide liquefaction with no signs of permafrost, though we know that it surrounds this area. There, we assume that the water circulation, in uenced by frozen layer upstream is a key factor. Scar n°3 shows only super cial erosion that contributes to gully recharge. Four processes of debrisow triggering related to permafrost can be highlighted: cohesion loss of sediments due to thaw in the matrix, cohesion reduction due to the constant creeping, spatio-temporal changes in water circulation and constant rejuvenation of sediment on the slope. For this site, the permafrost complex is a key factor for the triggering of debris ow, although we should take into consideration all other geomechanical processes that may occur in loose sediments.

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Published

2011-11-30

How to Cite

Bardou, E., Favre-Bulle, F., Ornstein, P., & Rouiller, J.-D. (2011). Influence of the connectivity with permafrost on the debris-flow triggering in high-alpine environment. Italian Journal of Engineering Geology and Environment, 13–21. https://doi.org/10.4408/IJEGE.2011-03.B-002