→ Mass movement = the downslope movement of rock/soil/mud due to gravity → usually triggered by heavy rain
● Scale of movement is determined by extent of weathering on the slope
○ Permeable = water can infiltrate
○ Impermeable = water cannot infiltrate
Sliding:
● Landslide = the downhill movement of a large amount of rock/soil/mud
○ Occur on steep/flat cliffs already weakened by weathering
● Process:
1. Heavy rain infiltrates soil and percolates into the rock
2. Saturated, heavy mass falls away along a fault/bedding plane
3. A block of potential landslide material is unsupported from below (wet rocks)
4. Layers of rock dip towards the sea and are liable to landslides
● Mudslide = the downhill movement of a large amount of wet mud
○ Occur where slopes are steep → take place very quickly
○ Occur where vegetation cover is sparse → cannot hold soil in place
○ Happen after a period of heavy rain
○ At base of mudslide → saturated soil spreads out to make a “lobe”
Rock fall:
● Bare rocks prone to freeze-thaw weathering
● Results in falling rocks losing contact with the cliff face
● At the bottom of the cliff → rocks spread form a scree slope
Slumping (rotational):
● Slumping = material is rotated backwards into cliff as it slips due to concave slip plane
● Process:
1. Rainwater soaks into porous sandstone/gravel which becomes saturated
○ Cannot penetrate the impermeable clay beneath it
2. Heavy, saturated rock bears down on the cliff → causes a curved slip plane to develop
3. A section of the cliff face tears away at the top of the curved slip plane
○ Gravity pulls the slab of rock down the the beach
○ Loose material collects at the bottom as a toe
4. Repeated rainfall events put pressure on the cliff and a new slip plane develops as material slumps
5. Waves remove the toe and undercut the cliff’s base to that it becomes unstable and slumps again