
15.2 What causes mass movements?
Fig 15.13
Friction and cohesion are resisting forces to gravity. Friction is an opposing force when two surfaces are in contact that increases with the "roughness" of contacting surfaces. Friction also varies with slope angle, as it is a function of mass and gravity. Cohesion is an attractive force between particles at the atomic level. Loose sand or gravel have little cohesion, but clay particles, with charged surfaces, have high cohesion.