Air photo showing rockfall in 1999

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

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.

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

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

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

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.

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

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.

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.

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

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

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.

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

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.

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.

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

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.

Rotational slip at Weybourne

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