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.
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.