A view on some hydrological triggering systems in landslides

In this paper different types of hydrological triggering systems for debris flows, shallow and deeper landslides are described. The generation of surface run-off and high peak discharges in first order alpine catchments is an important triggering mechanism for debris flows. Failure conditions in shallow landslides can occur when at a critical depth, which is determined by the cohesion of the soil and the slope angle, the moisture content in the soil becomes close to saturation, resulting in a considerable reduction of soil strength. Deeper landslides (5–20 m depth) are in most cases triggered by positive pore pressures on the slip plane induced by a rising ground water level. The assessment of meteorological threshold conditions for shallow landslides (1–2 m) needs more detailed meteorological information than for deeper landslides. In the analyses of the hydrological triggering systems of deeper landslides the presence of a permeable top layer and fissures has to be taken into consideration.