1. Air photo showing rockfall in 1999

2. Beachy Head after fall of 10th Jan. 1999
Beachy Head after fall of 10th Jan Undercutting of the base of the cliff helped to cause this fall.

3. Cliffs made of a well jointed rock like chalk are often undercut by wave action. When the wave-cut notch gets big enough the rock above will collapse.

4. A good example of a wave-cut notch at the foot of a cliff in California

5. Cave at foot of cliff formed
by wave action at Weybourne on the North Norfolk coast.

6. Coastal Processes
There are four main processes by which the sea can erode the land:

7. Hydraulic action is when air is trapped in a crack in a cliff by the sheer force of a wave.
There is an increase in pressure as the air is compressed which will break off pieces of rock. There is a sudden release of pressure as the wave retreats.

8. Corrasion is when waves throw sand, shingle and pebbles at a cliff and knock bits off it, slowly wearing it away

9. Solution: when certain rock types (e. g
Solution: when certain rock types (e.g. chalk) react with the sea, which is a weak acid. The rock dissolves in the water, turning it white.

10. Attrition is the knocking of rock fragments in the water against one another. The fragments are broken into smaller pieces and become smoother each time.

11. Non-Coastal Erosion Processes
There are two main non-coastal erosion processes:

12. Weathering Physical Weathering
Rain, hot weather and frost action help to break up the rock

13. Biological weathering
When burrowing animals (e.g. moles, rabbits, worms) and plant roots (trees and shrubs) disturb the soil and leave it more likely to be attacked by physical weathering.

14. Chemical weathering
Rainwater is slightly acidic and can dissolve certain rocks like chalk.

15. Human activity
When building takes place on cliff tops or when beach material is removed an increase in erosion may take place. Humans walking over gently sloping cliffs can have the same affect.

16. Wave erosion and weathering processes contribute to cliff collapse
Wave erosion and weathering processes contribute to cliff collapse. Most cliff collapse occurs during and after periods of heavy rainfall when water seeps into the land surface. This causes landslides and slumping under the effect of gravity.

17. Rotational Slip Heavy rainfall Stage 1
Steep cliff containing sand and clay
Water seeps
through the land to create a slide surface
Some water seeps out of the cliff
Stage 2
‘toe’ of slide
Material slides down onto the beach

18. Rotational Slip Stage 3 Small slides
Sea removes material from cliff base.
Stage 4
Weathering processes loosen the cliff.
Landslide becomes smaller due to wave erosion.

19. Rotational slip at Weybourne

20. This cliff at Weybourne collapsed because heavy rain this year saturated the rock and the sea undercut it.