Chesil & the Fleet: The Great Beach

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Chesil is one of the finest barrier beaches in the world.  It is made up of pebbles and shingle and has stood up to the full force of the Atlantic for thousands of years.

A National Treasure

Chesil is one of the finest barrier beaches in the world.  It is made up of pebbles and shingle and has stood up to the full force of the Atlantic for thousands of years.  It protects the Fleet, which is the largest tidal lagoon in Britain and a place on international importance for its birds and marine wildlife. Chesil and The Fleet are owned by the Ilchester Estate.

The beach is over 17 miles (28 km) long and increases in height towards the east, reaching a maximum of over 15 metres near Portland.  The pebbles also increase in size towards the east.  At West Bay they are pea-sized while at Portland they are the size of baking potatoes.  Local folklore claims that smugglers knew exactly where they had landed from the size of the pebbles on the beach.  Pebbles move east along the beach driven by the action of the wind and waves.  The grading of the pebbles may be because the larger pebbles move faster than smaller ones as the waves work on them.

The Fleet Lagoon

The Fleet Lagoon is a rich wildlife reserve which supports fresh, salt and brackish water species.  Underwater there are extensive meadows of eelgrass, whilst strong currents at the mouth of the lagoon allow an exceptionally diverse mix of seaweed, sponges and anemones to flourish.  A huge population of water birds rely on the lagoon.  They include the oldest managed swan population in the world, which can be visited at the Abbotsbury Swannery.

Building the Beach

The origin of Chesil Beach remains the subject of debate.  The traditional view is that the beach has been driven on shore by rising sea levels following the last Ice Age but the story might be more complex.

In the last interglacial period, about 125,000 years ago, sea levels were slightly higher than today and the landslides of West Dorset and East Devon were active.  During the last Ice Age, sea levels dropped.  The cliffs decayed into vast debris slopes that spilled across the exposed sea floor.  With the end of the Ice Age about 10,000 years ago, rising sea levels reached these huge landslides, releasing a vast amount of chert and flint onto the shoreline.  Longshore drift then carried the pebbles east, covering the beach that had been brought in by the rising sea and creating the massive structure we now see.

Today the beach is still moving on shore.  After stormy weather, lumps of peat are washed ashore from the seaward side of the beach.  They must be coming from sediments formed in a lagoon that lay further offshore when sea levels were lower over 4,000 years ago.