Formation of Chesil and the Fleet
Continuing research yields insights into the origin of the material that forms the beach and how it was transported to its current location. One possible theory for the formation of Chesil and Fleet comes from Malcolm Bray at Portsmouth University. Chesil Beach initially formed from predominantly sandy deposits in Lyme Bay, as water levels rose rapidly at the end of the last ice age, 20,000-14,000 years ago. The deposits were eroded, and the sand and gravel were driven onshore to form a barrier beach. As the beach was driven further east by rising sea levels, it overrode existing sediments, and the Fleet was formed about 7000-5000 years ago.
Sea level change and shingle movement
Sea levels stabilised 5000-4000 years ago, at that time Chesil stood close to its present position. It was predominantly sandy with layers of shell and coarser material, indicating overwashing by the sea. At this time, relic cliffs in East Devon that had been left stranded by falling sea levels during the ice age were reactivated. The combination of the reworking of extensive debris aprons and erosion of existing cliffs yielded large quantities of gravel. This material, estimated at up to 60 million cubic metres of gravel, was transported to Chesil by longshore drift.
A closed shingle system today
Geologist Dr Ian West suggested that coastal recession and human intervention have now depleted the beaches to the west of West Bay, resulting in increased prominence of the headlands. This has cut off the supply of material to Chesil. The beach must now be regarded as a closed shingle system with no replenishment from outside sources. It is therefore sensitive to environmental changes, such as rising sea levels. Ian West suggested that Chesil at Portland is moving eastward at around 15cm per year, with a much slower rate further north towards Abbotsbury.
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