Tree-Ring Reconstruction of Debris-Flow Events Leading to Overbank Sedimentation on the Illgraben Cone (Valais Alps, Switzerland)

Abstract

Dendrogeomorphological analyses of trees affected by debris flows have regularly been used to date past events. However, while previous studies in the Swiss Alps have focused primarily on granitic and gneissic debris-flow material and on Larix decidua Mill. and Picea abies (L.) Karst. trees, they have -at the same time -widely disregarded torrents dominated by finely fractured calcareous and dolomitic lithologies and forests populated with Pinus sylvestris L. In this paper, we report on results obtained from a debris-flow cone in the Rhone valley (Valais, Switzerland) where very fine and muddy material (limestone, dolomite, quartzite and calcite) occasionally affects P. sylvestris trees. Based on the results of a geomorphic map, 1004 increment cores from 451 disturbed P. sylvestris, 37 L. decidua and five P. abies trees were sampled, allowing reconstruction of 15 events between AD 1793 and 2005 as well as the determination of breakout locations of events. From the data, it also appears that debris-flow material only rarely left the incised channel over the last 200 years and that overbank sedimentation events did not occur after 1961, when a rockslide delivered large amounts of erodible material and subsequent debris flows caused an important incision of the canyon on the cone.

Quantitative reconstruction of late Holocene surface evolution on an alpine debris-flow fan

“…Our interpretation of the fan surface evolution over the past 3200 years is in disagreement with a dendrogeomorphic analysis of growth disturbances by debris flows in Stoffel et al (2008b). Those authors attributed growth disturbances to debris flows impacting trees in the vicinity of sample IG60 for several years in the nineteenth and twentieth centuries and as late as 1957.…”

“…Despite the frequency of debris flows in more humid environments such as the Swiss Alps (Hürlimann et al, 2003;Schlunegger et al, 2009), quantitative reconstruction of the timing and patterns of deposition on alpine debris-flow fans remains fairly limited. A number of studies have used dendrochronology to establish the timing and magnitude of debris flows on fans in the Swiss Alps (e.g., Stoffel et al, 2005Stoffel et al, , 2008aStoffel et al, , 2008bStoffel et al, , 2014Bollschweiler and Stoffel, 2010;Stoffel, 2010;Arbellay et al, 2010). This approach typically is limited to the last few hundred years and cannot therefore capture the evolution of the fan surface over Holocene time scales.…”

Dynamics of development and variability of surface degradation in the subalpine and alpine zones (an example from the Velká Fatra Mts., Slovakia)

“…Alpine geomorphological hazards such as avalanches, landslides and other demonstrations of slope instability may result from human activities as well as climatic variability factors, acting alone or in combination [22]. While the management of both landscape and human activities is important when considering the standpoint of the anthropic impact on the adverse effects of natural hazards, climatic factors play a significant role in the formation of geomorphological risks by affecting all the landscape elements [23].…”

Dendrochronological methods for reconstructing mass movements — An example of landslide activity analysis using tree-ring eccentricity

“…Tree-ring records may represent one of the most precise natural archives for reconstructing, and therefore understanding, past mass-movement events. Most dendrochronological studies concentrate on the reconstruction of the spatial and temporal distribution of different types of mass movements such as rock falls (Stoffel et al, 2005;Stoffel and Perret, 2006;, landslides (Shroder, 1978;Begin and Filion, 1988;Jacoby et al, 1992;Fantucci and Sorriso-Valvo, 1999;Gers et al, 2001;Stefanini, 2004;Migoń et al, 2010), debris flows (Baumann and Kaiser, 1999;Bollschweiler et al, 2007;Bollschweiler et al, 2008;Stoffel et al, 2008;Malik and Owczarek, 2009;Zielonka and Dubaj, 2009;Arbellay et al, 2010) and others (Denneler and Schweingruber, 1993).…”