The Illgraben Torrent System

The Illgraben catchment is one of the most active torrents in the European Alps, with between 2 and 7 debris flows or similar debris floods occurring every year since the start of systematic observations from 2000 to the present. The ultimate cause of the debris-flow activity is the presence of a variety of rock types, which have been substantially deformed and fractured due to tectonic processes. The change in the orientation of the major Alpine Simplon fault line resulted in the development of many additional faults, which is the cause of the highly fractured bedrock. Sediment delivery to the torrent-channel system is dominated by landslides, the deposits of which are temporarily stored within the channel. Subsequent mobilization of sediment, mainly by intense rainfall, results in the formation of debris flows and debris floods, which entrain the sediment within the torrent system and potentially endanger the community.