Mud flow

A mud flow (unconfined debris flow, often referred to as slope failure or slope-type debris flow) is a fast moving mixture of debris (pebbles, wood, soil, vegetation cover) and water originating on a steep slope. Superficial landslides sometimes trigger slope failures, however, very often there is no clear sliding surface present.

Mud flows Sachseln

Mud flows in Switzerland

In the presence of the corresponding trigger conditions (highly water-saturated soil horizons), unstable slopes, which account for 6% of the entire area of Switzerland also represent potential sources for the formation of slope failures. Like other landslide processes, slope failures also pose a threat to increasingly valuable buildings and infrastructure in Switzerland. 


Because mud flows constitute a mixture between a landslide and flow process, the availability of water plays a central role in their frequency and volume. Hence mud flowsare likely become more frequent and extensive in future as a result of climate change: due to the expected increase in heavy precipitation and an increase in winter precipitation combined with the rising snowline, more water will be available to trigger mud flows.