Coastal Processes Landslides Beaches Bays & Headlands Cliff falls		Beaches The evolution of Chesil Beach and the Fleet has been the subject of much discussion and remains the focus of considerable research today. Understanding where the beach came from is essential in order to determine what may happen to it and the land behind it in the future.
Cobbles, Chesil Cove Chesil Beach has protected the landscape behind it. If the beach were not there, the sea would be further inland and high cliffs would cut through the underlying geology		A number of features provide important clues to the formation of the beach: The beach runs from West Bay to Portland and is 29km in length. It increases in height towards Portland. The overall grading of the beach is from pea sized at West Bay to cobbles at Portland (although there are local variations that may be significant). Pea sized gravel, West Bay Most of the pebbles are locally derived flint and chert with some exotic material, notably quartzite pebbles from Budleigh Salterton in Devon. The core of the beach consists of a sand and pebble matrix of low permeability. The slope behind the beach is ancient and shows some signs of a raised shore line comparable to the Portland Bill raised beaches. If the beach were not there, the sea would be further inland and high cliffs would cut through the underlying geology. The Fleet lagoon contains sediments, including peats, that are at least 6 to 7,000 years old. The peat is being eroded on the seaward side of the beach and thrown onto it as large blocks while storm events push pebbles onshore, indicating that the beach is moving onshore.
		Peat sediments washed onto the beach from the seaward side during stormy weather, providing clear evidence that the beach is moving onshore, over the sediments that once formedin the Fleet lagoon
ANIMATION SEQUENCE: A possible theory for the formation of the beach 125,000 years ago: sea levels were higher than today Sea levels then dropped by over 100 metres Over the next 100,000 years the cliffs to the west became were exposed to weathering		The formation of Chesil Beach Long shore drift It has long been recognised that waves hitting a beach at an angle drive the beach materials in the direction that the waves are moving. Long shore drift animation 338kb in size The beach is exposed to the full force of the Atlantic and the long shore drift is predominantly to the east. This explains the occurrence of pebbles from Budleigh Salterton and more importantly, demonstrates that at least a proportion of the material that forms the beach came from the west. An early theory to the pebble gradation was that the strong south westerly gales carried all of the material to the east and that less strong waves from other directions carried the smaller pebbles back to the west. More recently it has been suggested that the larger pebbles move more rapidly due to their larger surface area. The local variations in pebble size both along and across the beach are thought to be significant but no satisfactory theory can yet explain it. Ice Age history The raised beaches on Portland Bill are 210,000 and 125,000 years old and clearly indicate a period when sea levels were up to 15 metres higher than today. The benches behind the Fleet lagoon are likely to be from the same periods of higher sea level. Sea levels then dropped to minus 45 metres below the present sea level 10,000 years ago. Since the end of the Ice Age, sea level has risen to its present position. Click here for an animation showing post glacial sea level rise (295kb)
Only about 20,000 years ago, sea levels rose once again, pushing a beach before it About 10,000 years ago, the rising sea levels struck the ancient landslides of West Dorset and East Devon, deliviering a vast volume of shingle to the east. Chesil Beach grew from the landslides The Fleet formed and peat settled in its base. Ongoing sea level rise is driving the beach over the peat sediments that are now exposed on the seaward side of the beach		Theories for beach formation There is no full agreement on the formation of the beach or any theory that can account for all of the observable phenomena. The traditional view is that Chesil Beach was driven onshore with rising sea levels at the end of the last Ice Age. As the sea advanced, material from what is now Lyme Bay was swept up to form the beach, trapping the Fleet lagoon in the process. More recently it has been proposed that a large volume of the beach was derived from the landslides of East Devon and West Dorset. During the last Ice Age, these landslides would have been very active indeed and as sea levels rose, erosion cut into the debris, sending a huge ‘pulse’ of material, by long shore drift, to the east. This might explain the older, finer beach that underlies what we see today. This beach moved onshore, trapping the Fleet lagoon and reaching its present position some 4 to 5,000 years ago. It was then buried by the pulse of shingle that forms the beach that we see today. Click here to see how the landslides may have fed Chesil Beach (File size: 338Kb) Click here for 3D Animation showing how Chesil Beach may have formed (1,380K) Or Click here for larger file (5,250K) Attention!......These are large files and unless you have fast internet access, will take a very long time to download. You will also require Windows Media Player, (version 6.4.07.1112 definitely works) The future The prospect that the beach is no longer supplied from the landslides presents serious implications and still leaves some important questions: If this theory is remotely correct, then Chesil Beach has now lost its supply of shingle and must be in terminal decline. The final section of the beaches and landslides animation shows the beach driving onshore to the point where headlands such as Golden Cap and Thorncombe Beacon appear, breaking the continuous beach and interrupting long shore drift. Certainly old Admiralty charts from the 17th century indicate a continuous beach, which is no longer, the case.
		A Coastal management issue
		The headlands effectively cut of the long shore drift but if the beach were just a short way further offshore, long shore drift could still have taken place The lack of shingle on the west side of the pier may be due to the dwindling supply from the west rather than the interruption to sediment movement created by the harbour entrance itself Some of the questions still to be answered include: How did the finer beach survive to protect the Fleet with its smaller volume and lower height? Why has the beach apparently migrated so slowly in the last 4 to 5,000 years? Were there other geographical features along this coast that may have had an effect on long shore drift when sea levels were lower? (There are a number of submarine rocky reefs exposed on the floor of Lyme Bay that must have played some part on the control of sediment movement).