Deep-seated landslides Sample Clauses

Deep-seated landslides. Large landslides present typically a volume of more than 1 million cubic meters. Slope angles for these types of slides in Switzerland are typically between 10° and 20°, with higher angles in alpine regions (Vulliet 1986). Due to their large extent (several km2) they show very often significant hydraulic and mechanical heterogeneities leading to different movement patterns within the sliding body. Large landslides are gravity-driven processes which are typically in a state of more or less constant movement with possible reactivation phases. They show however considerable differences among each other with respect to their velocities. Slow- moving landslides may reach velocities up to 1.6m/year and rapid-moving landslides reach velocities higher than 1.8m/h (Xxxxxx and Xxxxxx 1996; WP-WLI 1995). The following list presents some relevant features and processes in deep-seated landslides: • Majority of post-glacial slides with reactivation phases Slow-moving landslides are mostly encountered in regions which have been subjected to a relatively fast deglaciation period. Most large landslides have been moving for thousands of years. In most cases, movement takes place along pre-existing slip surfaces. The movement pattern is generally regular, but longer wet periods can lead to acceleration phases. • Groundwater fluctuations Climatic conditions are the main factors for changing movement activity, even if the variations of the hydrogeological and climatic conditions are in most cases not very marked (Xxxxxxxx et al. 2009). Large landslides present commonly a groundwater table primary subjected to seasonal fluctuations. Pore pressures along the failure plane are mostly positive. Fracture flow can play an important role in the hydrogeological system of the landslide. In the case of first-time failures, exceptional climate conditions are often the cause of instability. • Kinematic features Slow-moving landslides are slides which have either experienced progressive displacements over long time periods and are still active or went through a fast episode of movement in the past and now are only affected by residual movements. Such creeping behaviour (2-5mm/year) is in some cases associated to displacements due to seasonal groundwater table fluctuations (Xxxxxx et al. 2003; Xxxxxxxxx et al. 2004) and in other cases is told to be little affected by external events (Xxxxxxxxxx 2009). For cases of first time failure, rapid movements may arise for example from a sudden decre...