Chesil Beach is the seaward side of Chesil Bank, which stretches 29 km (18 miles) along the coast of Dorset. It has the effect of connecting the Isle of Portland to the mainland, trapping a tidal saltwater lagoon known as the Fleet. It is an example of a tombolo, the name given to a spit that reaches to an island.
Chesil Bank probably formed offshore and was driven onshore by waves and tides. It faces southwest towards the Atlantic and the prevailing winds, so it is in no danger of returning whence it came. That was also a problem in past centuries for sailing ships that found themselves driven on to the beach, because there was no way of setting the sails to allow an escape.
Like most storm beaches, Chesil is steeply sloped with a gradient of up to 45 degrees on the seaward side.
Chesil Beach is studied as an example of what happens under conditions of variable wave energy. At the Portland (eastern) end wave energy is much greater than at the western end. This means that smaller pebbles are washed offshore by the strong eastern waves but onshore by the weaker western waves. This graduated effect can be traced all along the beach, such that a blindfolded expert could tell exactly where he/she was if dumped at any point on the beach, simply by feeling the size of the pebbles, which are pea-sized at one end and potato-sized at the other.