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Spatio-temporal variability in debris-flow activity: a tree-ring study at Geisstriftbach (Swiss Alps) extending back to AD 1736 |
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| Authors: | Markus Stoffel Michelle Bollschweiler Susanne Widmer Annina Sorg |
| Institution: | 1. Laboratory of Dendrogeomorphology (dendrolab.ch), Institute of Geological Sciences, University of Bern, Baltzerstrasse 1+3, 3012, Bern, Switzerland 2. Climatic Change and Climate Impacts Group (C3i), Institute for Environmental Sciences, University of Geneva, 7, route de Drize, Carouge, 1227, Geneva, Switzerland 3. Katastrophenvorsorge, Amt für Milit?r und Bev?lkerungsschutz, Kanton Solothurn, Baselstrasse 40, 4500, Solothurn, Switzerland 4. Department of Environmental Sciences, Forest Ecology, Institute of Terrestrial Ecosystems, Swiss Federal Institute of Technology of Zurich (ETHZ), 8092, Zurich, Switzerland |
| Abstract: | Past debris-flow activity on the forested cone of the Geisstriftbach torrent (St. Niklaus, Valais, Swiss Alps) was assessed from growth disturbances in old conifer trees, providing a much improved record of past events. The study of 633 tree-ring sequences sampled from 252 European larch (Larix decidua Mill.), Norway spruce (Picea abies (L.) Karst.) and Silver birch (Betula pendula Roth.) trees allowed reconstruction of 53 debris-flow events since AD 1736. The spatial analysis of trees affected during particular events on the geomorphic map allowed for a spatial representation of individual events and a reconstruction of four flow patterns. Based on our results and Siegfried maps, we believe that before the formation of a dogleg near the cone apex in the late 1890s, debris flows preferentially used the channels located in the west-southwestern part of the Geisstriftbach cone. This study contributes to our understanding of debris-flow processes on cones and provides an example of how dendrogeomorphic techniques may help in the reconstruction and understanding of debris flows in Alpine areas. |
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