Landslides are naturally occurring phenomena in every environment on Earth, including the tropics, the temperate regions and the high latitudes, and in the oceans. Unfortunately, this ubiquitous natural process represents a substantial hazard to humans because people and structures have a surprisingly low capacity to withstand the forces generated by mobile soil and/or rock. In consequence, there is a long recorded history of landslide disasters – for example, Nihon Shoki (the ancient chronicle of Japan), which was completed in the year AD 720, describes numerous landslides and failures associated with the Hakuho earthquake on 29 November AD 684, whilst the city of Helike in Greece is believed to have been submerged and destroyed as a result of a submarine landslide in 373 BC. Today, landslides continue to inflict a substantial economic and social toll, especially in mountainous, less developed countries, and there is a widely held but admittedly poorly quantified expert perception that the impacts associated with mass movements are increasing rapidly with time.
The term landslide is unfortunately something of a misnomer as many landslides do not in reality involve sliding. The word landslide is used to describe a range of processes that result in downward and outward movement of slope-forming material composed of rock, soil and artificial materials. In this context the term ‘mass movement’ might be preferable, but here the term landslide will be retained as it is in such common use in this context.