Chesil Beach, located in Dorset, England, is a stunning 18-mile long tombolo made up almost entirely of pebbles of various rock types. The beach is a site of special scientific interest, with the pebbles increasing in size as you move eastward, ranging from pea-sized at West Bay to potato-sized at Portland. The pebbles are primarily composed of flint and chert from the Cretaceous and Jurassic rocks, as well as Bunter pebbles from the Budleigh Salterton area.
The Composition of Chesil Beach Pebbles
The pebbles on Chesil Beach are extremely hard, with a hardness of 6 on Moh’s Scale, making them harder than steel. The dominant flint and chert have been derived from Cretaceous rocks, possibly through Tertiary gravels such as those at Blackdown and Bincombe. The beach also contains some black chert from the Portland Cherty Series, the Portland Stone, and the basal Purbeck Formation, as well as limestone from the local Portland and Purbeck Formations.
| Rock Type | Percentage |
|---|---|
| Flint | 60% |
| Chert | 30% |
| Limestone | 10% |
Chert from the Portland Roach can be easily recognized due to the large molluscs and particularly the gastropod. The flint pebbles, and also chert and some other types of pebble, show conspicuous curved cracks or percussion marks, which are the results of numerous impacts on the beach when the pebbles have been thrown by waves.
The Geological History of Chesil Beach Pebbles
The pebbles on Chesil Beach have a fascinating geological history. They have been derived from various rock formations in the surrounding area, including the Cretaceous and Jurassic rocks, as well as the Bunter pebbles from the Budleigh Salterton area.
The flint and chert pebbles have been formed through a process of erosion and weathering over millions of years. The Cretaceous rocks, which are rich in these materials, have been gradually broken down and transported to the beach by rivers and streams. The Tertiary gravels, such as those at Blackdown and Bincombe, have also contributed to the pebble composition.
The limestone pebbles, on the other hand, have been derived from the local Portland and Purbeck Formations. These rocks have been eroded and broken down over time, with the harder limestone pebbles eventually making their way to the beach.
The Importance of Chesil Beach Pebbles
The pebbles on Chesil Beach are not just a geological curiosity; they play a crucial role in protecting the lowlands of Weymouth and the Fleet, which is considered one of the most important lagoons in Europe. The beach acts as a natural barrier, absorbing the energy of the waves and preventing flooding in the surrounding areas.
However, the removal of pebbles for commercial purposes has been discouraged to ensure the long-term survival of the beach. The pebbles are an essential part of Chesil Beach’s geological history and their preservation is crucial for the protection of the local environment.
Unique Features of Chesil Beach Pebbles
One of the most distinctive features of Chesil Beach pebbles is the size gradient. As you move eastward along the beach, the pebbles gradually increase in size, from pea-sized at West Bay to potato-sized at Portland. This size gradient is a result of the wave action and the sorting of the pebbles over time.
Another unique feature of the Chesil Beach pebbles is the presence of conspicuous curved cracks or percussion marks. These marks are the result of the pebbles being thrown by waves and colliding with each other on the beach. The hardness of the pebbles, which is higher than steel, allows them to withstand these impacts without breaking.
Conclusion
Chesil Beach’s pebbles are a unique and essential part of its geological makeup, providing both aesthetic and protective values to the area. The beach is a site of special scientific interest, and the preservation of its pebbles is crucial for the long-term survival of the local environment. Whether you’re a geology enthusiast or simply someone who appreciates the beauty of nature, Chesil Beach is a must-visit destination.
References:
– Wessex Coast Geology
– Chesil Beach Organization
– University of Washington Geology
– The Guardian