A landslide is the movement of rocks and soil down a slope and, when a large slide occurs in an area of dense human habitation, large numbers of people can be killed. In January 2011 mudslides in south-eastern Brazil killed more than 400 people.
Many natural events such as heavy rainfall, an earthquake or volcano can trigger a landslide, but human activities such as building construction can also cause or increase the chances of such an event.
Image: People recovering belongings after a landslide in southern Valle de Las Flores, La Paz, 27 February 2011 (credit: AFP/Getty Images)
Iain Stewart tells the story of Mount St Helens' 1980 eruption.
Professor Iain Stewart tells the story of Mount St Helens' 1980 eruption. An earthquake-triggered landslide unleashed a sideways blast of hot gas and ash from this famous stratovolcano volcano (also known as a composite volcano) in the state of Washington, USA.
A landslide or landslip is a geological phenomenon which includes a wide range of ground movements, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments. Although the action of gravity is the primary driving force for a landslide to occur, there are other contributing factors affecting the original slope stability. Typically, pre-conditional factors build up specific sub-surface conditions that make the area/slope prone to failure, whereas the actual landslide often requires a trigger before being released.