Correlation between climate, man and debris flow events — A palynological approach

Debris flows occur frequently in the high-alpine catchment area of lake Lago di Braies (1492 m a.s.l.). The sediments of the lake are used for detecting and dating past debris flow events during the last 4000 years and their driving factors. Comparing palynological and sedimentological data the results suggest, that mainly heavy precipitation in winter and summer as well as snow melt events in spring enhance the release of debris flow events. Therefore especially longer periods with humid and cool climate conditions show a clearly higher debris flow activity. The pollen diagram documents human impact on the catchment area since the late Neolithic, but the anthropogenic activities influenced the event activity only indirectly. Grazing and deforestation reduced the retention of debris by vegetation and results in thicker debris flow layers in the lake sediments.