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Coastal ProcessesBeaches Beaches are a large area of exposed material between low and high tide marks. The material that forms beaches is deposited by waves, which pick up sediments from the seabed and deposit them on the shore. When the waves hit the beach they lose force and deposit the sediment loads. Sediments on the Sefton coast are brought in from the Irish Sea. Sediment found on beaches varies from sand to cobbles. Most of the beaches along the Sefton coast are made up of sand although there is a shingle beach at Hightown, which is interesting as the cobbles are made up of waste from the demolition of houses. Sefton's beaches cover approximately 40,000,000m2 and contains approximately 260,000,000m3 of sediments above the -5m AOD contour.
To understand where the sediments come from to form beaches we need to go back in time to the last glaciation, the end of which was about 10,000 years ago. Massive glaciers covered the Irish Sea and as they moved they scraped against the rock beneath them. This rubbing action caused sediment to be eroded. The sediment was then deposited on the seabed when the glaciers melted and has lain there ever since. The action of waves and currents disturbs this sediment, the waves pick it up and carry it until it makes contact with land (beach) the wave loses force and drops the sediment and it is this sediment that forms the beaches. Beaches can be divided into three sections, backshore, foreshore and near shore. Near shore is the area up to the low water mark; foreshore is the area between low water mark and high water mark. Low water mark is the height on the beach of the low tide and high water mark is the height on the beach of high tide. This area is important for sediments as it takes the impact of waves. The backshore is from the high water mark to the dunes. This area is mainly dry and is only reached by the sea during storms. Beaches can be accreting or eroding, accretion is where sediments build up and erosion is where sediments are removed. The Sefton coast is subject to both processes. Volumetric analysis if Sefton's beaches show an increase between 2001 and 2002 but a decrease between 2002 and 2003. These changes represent less than 0.5% of the total beach volume. A good web site to visit to see how the coastline has changed is www.sandsoftime.hope.ac.uk/change/growth.htm This shows a diagram of the changes in the coast since 1845 to 1978.
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