Large slope instabilities have been frequently recognised in mountainous areas in different lithological (sedimentary, igneous, metamorphic rocks) and geological domains (cordillera, volcanic, etc.). Slow to very fast moving, complex mass movements have been recognized and sometimes described as strongly interrelated. Many types of slope instabilities can be grouped within this broad class, each presenting different types of hazard and risk. Some major aspects of these slope instabilities are still understudied and debated, namely:
- their regional distribution and relevance;
- triggering and controlling factors, including possible climatic changes;
- dating of initial movements and reactivation episodes;
- style and state of past and present activity;
- passive and/or active control by structural-tectonic elements of the bedrock geology;
- hydrological boundary conditions;
- possible evolution and modelling;
- assessment of related hazard;
- influence of external anthropogenic factors and effects on structures;
- role on the general erosional and sediment yield regime within a mountain belt;
- best technologies and approaches for implementing a correct monitoring and warning system and for the interpretation of monitoring data in terms of landslide activity and behavior.
Study of these instabilities requires a multidisciplinary approach involving geology, geomorphology, geomechanics, hydro-geochemistry, and geophysics.
Trenching and drilling can be used for material characterization, recognition of episodes of activity, and sampling in slow slope movements. At the same time many different approaches can be used for monitoring and establishing of warning thresholds and systems for such phenomena.
Geophysical survey methods can used to assess both the geometrical and geomechanical characteristics of the unstable mass. Different dating techniques can be applied to determine the age of movements. Many modelling approaches can be applied to evaluate instability and failure(displacement and velocity thresholds, etc.), triggering mechanisms (rainfall, seismicity, volcanic eruption, deglaciation, etc.), failure propagation, rapid mass movements (rock avalanches, debris avalanches and flows), and related secondary failures (rock fall and debris flows).
Studies of hydraulic and hydrologic boundary conditions and hydrochemistry are involved, both at the moment of initial failure (e.g. during deglaciation) and, later, during reactivation. The impacts of such instabilities on structures and human activities can be substantial and of a variety of forms (e.g. deformation or failure of structures and infrastructure, burial of developed areas, etc.).
Furthermore, the local and regional sediment yield could be influenced by the landsliding activity and different landslides (e.g. type, size) can play different roles.