Debris-flood reconstruction in a pre-alpine catchment in Switzerland based on tree-ring records of coniferous and broadleaved trees
The AA. present a case study of a debris-flood fan covered with coniferous and broadleaved tree species affected by past torrential activity in a pre-alpine catchment with limited sediment supply. The reconstruction is based on the sampling of 148
trees on the fan of the Torrent de la Greffe, Valais, Switzerland. Through the analysis of the trees sampled and their spatial distribution on the fan surface they analyse the debris-flood frequency of the torrent and the spatial imprint of past events.
Dendrogeomorphic reconstruction of past debris-flow activity using injured broad-leaved trees
This study aimed at dating the occurrence of former debris flows from growth series of broad-leaved trees and at determining their suitability for dendrogeomorphic research. Results were obtained from gray alder, silver birch and pubescent birch
, aspen, white poplar, black poplar and gray poplar, goat willow and black elder injured by debris-flow activity at Illgraben (Valais, Swiss Alps). Tree-ring analysis of increment cores, wedges and cross-sections from injured broad-leaved trees allowed
tree loss on reconstructed tree-ring analysis. The study investigated the Bärenrüfe torrent located in the province of Vorarlberg. Based on 3 annual field observations, it is evident that this catchment produces very frequent and small debris flows
with minor material relocation. The specific challenges of tree-ring analysis in this tree species and in highly active environments are explicitly addressed in the discussion and underline the necessity of employing complementary methods of analysis
to channels. To understand the connectivity between hillslopes and channels and between sources and sink, trees were sampled along the main Rossloch stream, on the Schimbrig earth flow and on the Rossloch depositional area. Geomorphic observations
and dendrogeomophic results indicate different mechanisms of sediment production, transfer and deposition between upper and lower segments of the channel network. Tree analysis allowed the reconstruction of periods of high activity during the last century