any downhill movement of material is called mass movement eg rock falls caused by freeze thaw in resistant rock. mass movement occurs in cliffs formed in less resistant rock such as sands and clay, which are more easily eroded. these cliffs are eroded at the foot by the sea, but the cliffs themselves can become waterlogged by rainfall causing them to become unstable and leading to land slips also called rotational slumping.
processes of erosion by waves
waves erode the coastline in four main ways:
1. Abrasion or corrasion: the sea hurls pebbles and sand against the base of the cluff, chipping and grinding it down
2. Hydraulic action: powerful waves lash teh cliffs, forcing air into tiny cracks. the pressure of the compressed air weakens the rock and forces it to break up
3. Corrosion: the sea water may react with chemicals and minerals in some rocks and they can be dissolved
4. Attrition: the rocks and stones that the sea erodes from the cliffs are rounded and broken as they bump against each other and they are thrown against the cliff
processes if transportation and deposition
the largest materials such as boulders are rolled along the sea floor by waves (traction); smaller materials such as pebbles are bounced (saltation); finer material such as sand is carried in suspension and soluble materials such as limestone is dissolved and carried in solution.
the movement of material by waves along the coast is called longshore drift. the movement of sediment depends on the direction of the prevailing wind.
sediment is deposited where the sea no longer has enough energy for it to be transported. this happens in areas of calm water e.g. in a bay
caves, arches and stacks
erosion of a headland
1. cracks show weakness in the rock,
2. sea attacks line of weakness, opening up the crack
3. as the crack is eroded further, a cave is formed
4. if the cave is eroded right through the headland, an arch is formed
5. wind, rain, snow and frost attack the top of the cliff
6. the arch will eventually collapse as it is widened by the sea and worn by the weather, leaving a stack
7. the weather and sea attack the stack until a stump is left, often covered by water at high tide
beaches are formed from material deposited between high and low water marks. some are wide and sandy and ofter backed by sand dunes; others may be built of shingle or pebbles and these often have steeper gradients. beaches are always changing as material is removed and replaced by new material brought by longshore drift
long narrow deposits of sand or shingle, which extend from the land out intop the sea, are called spits. spits develop where the coastline changes direction or is interrupted by an estuary. the seaward end of the spit is in deeper water and may be curved because of the effect of winds and sea currents. fresh and salt water are trapped behind the spit as it develps and mud flats and salt marshes build up in the sheltered area on the landward side of the spit. a well known example of a spit is spurn head, which extends for 4.8km across the humber estuary
sometimes material is deposited right across a bay or inlet in the coastline forming a sand bar. this cuts off the water behind it, which froms a lagoon. this may eventually disappear and become colonised by plants