The Jurassic Coast Trust and the Environment Agency have issued a warning for people to keep away from the East Cliffs at West Bay following a cliff collapse on Wednesday 13 March 2019. About a thousand tonnes of rock fell from the cliff onto the beach without any warning, narrowly missing several passers by, although fortunately nobody was hurt. The site was inspected shortly after by geologist Sam Scriven of the Jurassic Coast Trust, who has warned that the cliff remains unstable and further collapses are likely.
Rockfall on the beach beneath the East Cliffs at West Bay this week. Sam Rose/Jurassic Coast Trust/Dorset Echo.
The cliffs at East Bay are made up of two main layers, the Bridport Sands at the base, and the Inferior Oolite (limestone made up of egg-shaped particles) above. These cliffs are usually very stable, but in very wet conditions, such as those experienced by the UK this week, the sandstones can become waterlogged and lose their cohesion, causing collapses which undermine the limestones above. Landslides are a common problem after severe weather events, as excess
pore water pressure can overcome cohesion in soil and sediments,
allowing them to flow like liquids. Approximately 90% of all landslides
are caused by heavy rainfall.
The East Cliffs at West Bay, seen from Burton Bradstock. UK Fossils.
The beaches of Dorset are famed for their numerous Jurassic fossils, which attract many people to the area. These fossils are produced by erosion of the cliffs, and collected by both amateur enthusiasts and professional palaeontologists from the beaches below (direct excavation from the cliffs is strictly forbidden, due to the dangers of rockfalls). The beaches at West Bay are not usually considered among the better fossil collecting spots in the region, due to the stability of the cliffs, which means that new fossils arriving on the beach is a rarity. However, the Inferior Oolite is noted for its many well preserved Ammonite fossils, which can be found on the beaches after rockfalls such as the one that occurred this week. This is problematic for site managers with the Jurassic Coast Trust, as it means that people will often try to access the site immediately after rockfalls, in the hope of finding the best fossils before other collectors arrive, rather than waiting for the area to be declared safe.
Simple geological section of the cliffs at West Bay. Ian West/Geology of the Wessex Coast of Southern England/University of Southampton.
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