Spatial analysis of rockfall activity, bounce heights and geomorphic changes over the last 50 years – A case study using dendrogeomorphology |
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| Authors: | DM Schneuwly M Stoffel |
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| Institution: | aLaboratory of Dendrogeomorphology, Department of Geosciences, University of Fribourg, Chemin du Musée 4, 1700 Fribourg, Switzerland |
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| Abstract: | Tree-ring series have been used to reconstruct 50 years of rockfall behavior on a slope near Saas Balen (Swiss Alps). A total of 796 cores and 141 cross sections from 191 severely injured conifer trees (Larix decidua Mill., Picea abies (L.) Karst. and Pinus cembra L.), combined with a series of aerial photographs, were used to investigate the evolution of the forest stand so as (i) to reconstruct past rockfall rates; (ii) to analyze the spatial behavior of maximum bounce heights; and (iii) to analyze the spatial comportment of rockfall activity over the last five decades.Tree-ring analysis permitted the reconstruction of the age distribution at the study site; results were in perfect agreement with the afforestation process shown in the aerial photographs. The oldest are located in the lower, central part of the study site; the youngest individuals at its uppermost lateral boundaries. Reconstructed rockfall rates reveal strong interannual variations and single event years with increased activity, namely in 1960/1961 and 1995. Spatial analysis of the maximum bounce heights indicate highest values at the lateral boundaries and lowest heights in the lower central part of the forest stand, where a big boulder seems to shield trees growing below it. The spatial analysis of past rockfall activity shows high active zones at the uppermost north-facing boundaries of the forest and least active zones in the lowermost central part of the studied stand. The high rockfall activity at the slope is expressed by a mean rockfall rate of > 1 event m− 1 y− 1. |
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| Keywords: | Dendrogeomorphology Tree-ring Rockfall Spatial analysis Frequency GIS |
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