Debris flow

A debris flow is a pap-like, very often fast flowing mixture of water and solid components (sand, gravel, stones, blocks, wood) with a high proportion of about 30 to 60%.

Debris flow Ergisch

Debris flows in Switzerland

Many historical settlements in the Alpine valleys were established on debris-flow cones which could provide the population with protection against the flooding of the valley floors. Settlements arose in particular in areas located at a distance from river channels as this meant that the risk of debris flow was small as compared with that posed by flooding. Due to increased settlement pressure and economic growth, these settlements expanded and the material assets exposed to risk have increased. Today’s settlements often cover large areas of these debris-flow cones. As a result, debris flows and their consequences (e.g. large-scale debris flows on the cones) often cause material damage and, given the difficulty in predicting these processes, unfortunately also, injury to persons.


Some recent events clearly demonstrate the serious consequences that debris flows can have in Switzerland:

Debris flow deposition Baltschiederbach
  • On 14 October 2000 13 people died in a debris flow in Gondo which destroyed large parts of the mountain village.
  • The intensive precipitation in August 2005 resulted in the formation of a debris flow in the Glyssibach torrent near Brienz, which, in addition to extensive material damage, also caused two fatalities.