Faculté des sciences

400 years of debris flow activity and triggering weather conditions: Ritigraben VS, Switzerland

Stoffel, Markus ; Lièvre, Igor ; Conus, Delphine ; Grichting, Michael A. ; Raetzo, Hugo ; Gärtner, Holger W. ; Monbaron, Michel

In: Arctic Antarctic and Alpine Research, 2005, vol. 37(3), p. 387-395

Three major rainfall events have caused considerable damage in the Valais region (Swiss Alps) since 1987. While important debris flows originating from periglacial environments were recorded during the August 1987 and September 1993 rainfall events, no debris flows occurred in October 2000. This paper aims at putting these large area events and the apparent increase in debris flow frequency into... More

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    Summary
    Three major rainfall events have caused considerable damage in the Valais region (Swiss Alps) since 1987. While important debris flows originating from periglacial environments were recorded during the August 1987 and September 1993 rainfall events, no debris flows occurred in October 2000. This paper aims at putting these large area events and the apparent increase in debris flow frequency into a wider context by reconstructing the past debris flow activity in the Ritigraben torrent (Mattertal, Valais) with dendrogeomorphological methods. While only 10 debris flows were known for the torrent before the analysis (1922-2002), 53 events could be reconstructed with tree-ring analysis, going back to the year 1605. Results further show that the above-average concentration of events since 1987 was mainly caused by insufficient and short archival data. In fact, debris flows occurred even more frequently in the 19th century than they do today. The spatial distribution of injured trees in particular years further indicates that important events, like in 1993, always occurred in the torrent. Finally, reconstructed event years were compared with archival data on flooding in neighboring catchments. The comparisons prove that large area events like in 1987, 1993 or 2000 have at least been as common in the past as they are today.