Landslide

Landslide in Pakistan

A landslide includes a wide range of ground movements, such as rock falls, deep failure of slopes and shallow debris flows.

The biggest reason for a landslide is that there is a slope and material goes down the slope because of gravity.

But other things also contribute to landslides:

erosion by rivers, glaciers, or ocean waves makes slopes too steep
rock and soil slopes made weak through saturation by snowmelt or heavy rains
earthquakes that make weak slopes fail or crack the rocks that will eventually fall down
volcanic eruptions produce loose ash deposits, heavy rain, and debris flows
vibrations from machinery, traffic, blasting and even thunder may trigger failure of weak slopes
weight from much rain or snow, stockpiling of rock or ore, from waste piles, or from buildings may stress weak slopes to failure and other structures
groundwater pressure making the slope unstable
in shallow soils, the removal of deep-rooted plants that bind the colluvium to bedrock

An underlying reason is the nature of the material. For example, a thixotropic material such as mud or sand and water, can change from a gel to a sol by adding water or pressure, or shaking. It goes from being stable one minute to fluid the next minute. The greatest disasters, like lahars or mudslides, happen suddenly. It is possible for much of a volcano to just slide down suddenly, as with Toba, Krakatoa and Mount St Helens.

Landslide Media

A landslide near Cusco, Peru, in 2018
A NASA model has been developed to look at how potential landslide activity is changing around the world.
Animation of a landslide in San Mateo County, California
The Mameyes Landslide, in the Mameyes neighborhood of barrio Portugués Urbano in Ponce, Puerto Rico, was caused by extensive accumulation of rains and, according to some sources, lightning. It buried more than 100 homes.
The landslide at Surte in Sweden, 1950. It was a quick clay slide that killed one person.
Diagrams of ten major types of landslide movement depicting the nature of the movement and the resulting landforms.
The Costa della Gaveta earthflow in Potenza, Italy. Even though it moves at a rate of just a few millimeters per year and is hardly visible, this landslide causes progressive damage to the national road, the national highway, a flyover, and several houses that are built on it.
A rock slide in Guerrero, Mexico
Hotel Panorama at Lake Garda. Part of a hill of Devonian shale was removed to make the road, forming a dip-slope. The upper block detached along a bedding plane and is sliding down the hill, forming a jumbled pile of rock at the toe of the slide.
Deep-seated landslide on a mountain in Sehara, Kihō, Japan caused by torrential rain of Tropical Storm Talas