Causes of landslides

The causes of landslides' are usually related to instabilities in slopes. It

is usually possible to identify one or more landslide causes and one landslide trigger.

The difference between these two concepts is subtle but important. The

landslide causes are the reasons that a landslide occurred in that location and

at that time. Landslide causes are listed in the following table, and include geological factors, morphological factors, physical factors and factors

associated with human activity.

Causes may be considered to be factors that made the slope vulnerable to failure, that

predispose the slope to becoming unstable. The trigger is the single event that finally initiated the landslide. Thus, causes combine to make a slope vulnerable to failure, and the trigger finally initiates the movement. Landslides can have many causes but can only have one trigger as shown in the next figure. Usually, it is relatively easy to determine the trigger after the landslide has occurred (although it is generally very difficult to determine the exact nature of landslide triggers ahead of a movement event).