Unraveling the patterns of late Holocene debris-flow activity on a cone in the Swiss Alps: Chronology, environment and implications for the future

Article Article scientifique Article Unraveling the patterns of late Holocene debris-flow activity on a cone in the Swiss Alps: Chronology, environment and implications for the future eng 2008 author Stoffel Markus 131626 author Conus Delphine author Grichting Michael A. author Lievre Igor Maurice Armand 40776 author Maître Gilles 222-234 10.1016/j.gloplacha.2007.03.001 0921-8181 https://linkinghub.elsevier.com/retrieve/pii/S0921818107000446 Debris-flow activity on the forested cone of the Ritigraben torrent (Valais, Swiss Alps) was assessed from growth disturbances in century-old trees, providing an unusually complete record of past events and deposition of material. The study of 2246 tree-ring sequences sampled from 1102 Larix decidua Mill., Picea abies (L.) Karst. and Pinus cembra ssp. sibirica trees allowed reconstruction of 123 events since AD 1566. Geomorphic mapping permitted identification of 769 features related to past debris-flow activity on the intermediate cone. The features inventoried in the study area covering 32 ha included 291 lobes, 465 levées and 13 well-developed debris-flow channels. Based on tree-ring records of disturbed trees growing in or next to the deposits, almost 86% of the lobes identified on the present-day surface could be dated. A majority of the dated material was deposited over the last century. Signs of pre-20th century events are often recognizable in the tree-ring record of survivor trees, but the material that caused the growth anomaly in trees has been completely overridden or eroded by more recent debris-flow activity. Tree-ring records suggest that cool summers with frequent snowfalls at higher elevations regularly prevented the release of debris flows between the 1570s and 1860s; the warming trend combined with greater precipitation totals in summer and autumn between 1864 and 1895 provided conditions that were increasingly favorable for releasing events from the source zone. Enhanced debris-flow activity continued well into the 20th century and reconstructions show a clustering of events in the period 1916–1935 when warm–wet conditions prevailed during summer in the Swiss Alps. In contrast, very low activity is observed for the last 10-yr period (1996–2005) with only one debris-flow event recorded on August 27, 2002. Since sediment availability is not a limiting factor, this temporal absence of debris-flow activity is due to an absence of triggering events, which not only shifted from June and July to August and September over the 20th century, but also seemed to be initiated primarily by persistent precipitation rather than summer thunderstorms. From the reconstructions, based on RCM simulations, there are indications that debris-flow frequencies might continue to decrease in the future, as precipitation events are projected to occur less frequently in summer but become more common in spring or autumn. Previous article in issue Debris flow Tree-ring analysis Dendrogeomorphology Deposition processes Climate change Swiss Alps Dewey 333.7-333.9 18 Institut des sciences de l'environnement 0DB false 915 Climatic Change and Climate Impacts Global and Planetary Change 60 3-4 545d2baf-f8a5-4026-be93-d754937f0e47 Article (Published version) Restricted Stoffel2008.pdf 2028948 application/pdf restrictedAccess Centres et instituts / Institut des sciences de l'environnement

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Unraveling the patterns of late Holocene debris-flow activity on a cone in the Swiss Alps: Chronology, environment and implications for the future	Global and Planetary Change			2008	337	0

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Lievre, Igor Maurice Armand