Unusually High Amounts of Precipitation
High amounts of rainfall are thought to have been one of the causes of the Gros Ventre slide. The water can act as a lubricant, causing already unstable layers of earth to succumb to the forces of gravity and begin moving downhill.
This is the second factor that is thought to have brought about the Gros Ventre slide. Earthquakes can shake up and disturb layers of soil, causing them to become unstable and move downhill. If you add high amounts of precipitation to the mix, you can get an effect known as liquefaction.
Liquefaction takes place when loosely packed, water-logged sediments at or near the ground surface lose their strength in response to ground shaking. If this occurs beneath buildings or structures, it can cause the ground to lose its firmness and the buildings sink. In the case of a landslide, it can cause upper layers of earth and debris to become unstable and through the forces of gravity move downhill.