Coastal Features: The Chesil Beach (Chesil Bank), Pebble Size and Longshore Drift
The Chesil Beach (Chesil Bank)
Consisting of a 100 million ton bank of pebbles, the Chesil Beach stretches for 28 km to West Bay.
The beach varies between 36 and 200 meters wide and also in height, being 14 meters at Portland and just 5 meters at West Bay. The bank of pebbles separates the sea from Britainís largest tidal lagoon, the Fleet, an important wildlife habitat for all manner of extraordinary flora and fauna. The beach is marching inland at a rate of 5 meters every century, reducing the size of the Fleet Lagoon in the process.
The Chesil Beach is by no means stable. Storm waves have breached its pebble bank several times in the past, flooding the Fleet Lagoon, the land behind it and Portland to a depth of several meters. In one great storm the beach was swept away, exposing the underlying Kimmeridge Clay, in which were coins, jewelry and all sorts of artifacts that had been lost between the pebbles throughout the centuries.
Pebble Size and Longshore Drift
The stones that make up the Chesil Beach are mainly derived from East Devon, consisting of Metaquartzites of the Ordovian and Devonian Age, Chert and Flint. A unique feature the Chesil Beach is how the pebble size changes from one end to the other. Large cobbles are found at Chesil Cove, Portland, while West Bay has fine grit and gravel. It is thought the bigger heavier stones have a larger surface area and are therefore carried further to the east by the powerful prevailing south westerly waves hitting the beach at an angle, while the smaller lighter stones are carried back to the west by the less powerful waves approaching from the south east.
In effect the stones zigzag their way along the coastline, carried by this longshore drift, accounting for the size graduation.
The harbours at Lyme Regis and West Bay are both obstacles to the longshore drift, and the reduction in quantity of stone being delivered through coastal erosion in East Devon is diminishing. The long-term future
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Interest: The Chesil Beach and Smugglers
The Chesil Beach and Smugglers
Folklore says that a local fisherman or smuggler could tell exactly where he was on the beach at night or in fog simply by looking at the size of the pebbles. This aided him in sneaking ashore, away from the customs men and their patrols.