Large slope instabilities have been recognised in mountainous areas in different lithological and geological domains, and on other planets. Slow to extremely 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 debated:
- regional distribution and relevance;
- presence, distribution and significance of phenomena on other planets;
- triggering and controlling factors;
- dating of initial movements and reactivation episodes;
- style and state of past and present activity;
- passive and/or active control by structural-tectonic elements;
- hydrological boundary conditions;
- possible evolution and modelling;
- assessment of related hazard;
- influence of anthropogenic factors and effects on structures;
- role on the erosional and sediment yield regime in drainage catchments and mountain belts;
- technologies for monitoring and warning systems, and the interpretation of monitoring data.
Study of these instabilities involves geology, geomorphology, geomechanics, hydro-geochemistry, and geophysics. For landslides on other planets a few of these approaches can be adopted making more difficult the interpretation of the phenomena, the identification of triggerings and controlling factors.
Trenching and drilling can be used for material characterization, recognition of activity episodes, which can be combined with monitoring data for establishing of warning thresholds and systems.
Geophysical survey methods can describe both the geometrical and geomechanical characteristics of the unstable mass. Dating techniques can be applied to determine the age of movements. Modelling can be applied to evaluate instability and failure, triggering (rainfall, seismicity, volcanic eruption, deglaciation), failure propagation, collapse (rock avalanches, debris avalanches and flows), and secondary failures (rockfall, debris flows).
Different hydraulic and hydrologic boundary conditions and hydrochemistry are involved, both at failure and during reactivations. The impacts of such instabilities on structures and human activities can be substantial and of a variety of forms. 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.