What is the most common factor leading to slope instability?

The most common factor leading to slope instability is the removal of lateral support. When lateral support is taken away, whether through human activities such as excavation, construction, or natural processes such as erosion, the stability of the slope is compromised. Lateral support refers to the material that holds a slope in place on its sides; when it is removed, the balance of forces acting on the slope is disrupted, leading to potential failure.

This destabilization can result in landslides, rockfalls, or other forms of mass wasting, as the weight of the materials above may no longer be adequately supported. While factors like excessive rainfall, soil saturation, and earthquake activity can indeed contribute to slope failure, they often act as secondary factors or triggers that affect previously stable slopes. The initial loss of lateral support is frequently the critical factor that leads to the breakdown of slope stability.