Coastal Erosion

Erosion is the wearing away on the land by material carried by rivers, glaciers, waves, and wind. The two main factors that affect the rate of erosion of our coasts; the power of the waves and the resistance of the land that the wave strikes. The most destructive wave occurs during storms but even quite moderate waves can have a big effect over a long period of time. Hardrock such as Granite can withstand this attack for much longer than sand or clay, but there is no type of coast that can avoid the massive erosive force of the seas and the oceans forever. Waves are the agents of coastal erosion, they are mainly caused by winds but tides can have an effect. Waves are particularly strong when there is a long fetch which is the distance they are able to travel in a straight line, before they reach land. They are also affected by how deep or shallow the sea is as they approach land. Waves erode land in the smae way rivers erode their beds.

The different types of coastal erosion are on the next card...

The types of coast erosion are: 

• Hydraulic Action -It is a force of the water itself or of air trapped by water from caves or crack in the rock. 

• Corrasion - This is where the rocks and pebbles in the water hit the shore.

• Attrition - This is where the rocks and pebbles hit against each other.

• Corrosion - Which is where the water dissolves certain types of rock.

Weathering is the breaking up and decay of rocks in situ (their place of origin).

There are three main groups of weathering that take place at the coast:

• Physical Weathering 
• Freeze-Thaw - When water enters the cracks in the rocks, the temperature drops and the water freezes. As water freezes, it expands and puts pressure on the rock. 
• Exfoliation - Repeated heating and cooling. Rocks expand when hot and contract when cold, causing the rock to crack.
• Chemical Weathering
  
• This is when the decomposition(decay) of rocks caused by a chemical change within a rock. (Acid Rain)
• Biological Weathering
• This is caused by the action of animals and plant roots, which dislodge rocks.

• Due to the prevailing wind on the coast line; clasts are carried by the swash up the beach. This occurs in the same direction as the prevailing wind and therefore is at the same angle.
• Following the swash, the clast is then carried back down the beach, in a straight line due to gravity (perpendicular to the beach).
• This process repeats and the clast is carried b the swash and the backwash along the beach in a process called LONGSHORE DRIFT.

A spit is a depositional feature, it is formed by longshore drift with extent of a headland. 

• Spits are formed in shallow, sheltered water when there is a change in direction of the coast line.
• Longshore drift transports materials along the coastline.
• Deposition occurs resultng in an accumilation of sand and shingle.
• The material intially desposited is the largest material dropped due to the reduction of energy.
• Finer material is then deposited helping to build up the rest of the spit. 
• As the spit grows outwards, a change in wind direction may result in a change in direction of a spit forming a hook/curved end.
• If growing acroos a river estuary, the length of the spit will be restricted.
• A salt marsh may form in the sheltered, low energy zone behind the spit.