Original paper

A six-year record of debris transport by avalanches on a wildfire slope (Arnspitze, Tyrol)

Sass, O.; Heel, M.; Hoinkis, R.; Wetzel, K.-F.

Abstract

Debris deposition by avalanches was monitored for six years at the Arnspitze south slope in the North-Tyrolean Limestone Alps. The slope investigated was deforested by a severe wildfire event in 1946 and is still largely vegetation-free today. We collected avalanche-transported debris on the snow fields at the base of the slope after ground avalanches in spring. The results show mean sediment yields of 126 t km-2 a-1; the mean erosion rate is 48 mm ka-1 for bedrock or 70 mm ka-1 for soil/debris, respectively. These values are much higher than most previous measurements reported in the literature. Avalanche erosion is extremely variable between the years, ranging from 0 t to 215 t per year. The thickness of the snow cover, the timing of the spring melt, debris storage in the preceding years and unknown random factors appear to be responsible for the temporal variations. There are also large spatial differences between the sub-catchments. The highest absolute removal (in tonnes) occurs in the largest catchments; the correlation between catchment size and removal rate (tonnes per unit size) is positive but weak. The investigations indicate that process equilibrium remains disturbed, even after more than 60 years have elapsed.

Keywords

avalancheerosionsediment yieldwildfirealps