Earthquakes

Ground shaking can increase downslope force. Ground shaking can also separate particles of regolith and decrease the friction that holds them together.

Rivers and roadcuts

Steeper slopes are subject to greater downslope force. Rivers often undercut their banks and make them steeper. Roadcuts may make slopes steeper and more likely to fail.

Ground saturation

As soils become saturated, they become heavier, and the downslope force increases. Saturation moves soil particles farther apart, reducing friction between them. Mass movement commonly follows storms that bring heavy, soaking rains. Broken water pipes on steep slopes can also lead to mass movement.

Weathering

Increased weathering weakens the integrity and strength of rocks and regolith.

Removal of vegetation

Removal of vegetation and its anchoring roots weakens the ground and decreases the resistance force.