Frequenz und Fliesshöhen der Plattlaui (Uri), rekonstruiert mithilfe von Jahrringen

Abstract

Frequency and flow heights in the Plattlaui avalanche couloir (Uri) – a reconstruction based on tree growth rings The Maderaner Valley (Uri) is one of the regions in Switzerland most heavily affected by snow avalanches, and in the past has also regularly been ravaged by devastating events. The present article is intended to contribute to the database of known avalanche events, and to improve understanding of past avalanche activity. In order to do this, the annual rings of spruce trees (Picea abies [L.] Karst.) were investigated for growth disturbances which could indicate the frequency and flow height of past avalanches in two adjacent couloirs of the Plattlaui avalanche track. The dendromorphological analysis was based on growth ring samples taken from a total of 42 spruce trees on a transect at an altitude of 1570 m. The occurrence of past snow avalanches was primarily reconstructed from evidence of injuries and the associated tangential rows of traumatic resin ducts, but also included abrupt growth suppression, sudden increase in increment and the presence of compression wood. Altogether 19 avalanche events extending back to 1940 were reconstructed and the flow height of individual events demonstrated. Based on the spatial distribution of damaged trees, it was possible to distinguish between unusually high (2 events; 1986, 1999), high (7), medium (7) and small (3) flow heights of snow avalanches. The growth ring reconstruction contains considerably more events (19) than the local archive indicates (7), but fails to document two of the known events. The study therefore also demonstrates the limits of the approach in the case of low flow height avalanches, and at the beginning of the reconstruction with fewer trees available for analysis.