A pipeline runs into this bay from the now disused Winfrith Atomic Energy Research Establishment. There was a shipwreck in the way of the pipelines intended path, so the American Liberty Ship, the “Black Hawk” was set with charges and blown in two! This area lies within the MOD’s Lulworth Firing Range, but visitors are free to explore when the range walks are open to the public.
Coastal Features: The Great Unconformity and The Cretaceous Blanket, Chalk Cliff Erosion, Mupe Bay and Worbarrow Bay
Mupe Bay and Worbarrow Bay
The geology of Worbarrow Bay and Mupe Bay is very similar and they almost mirror one another, with the mirror being where the two bays meet at Arish Mell Gap. They both consist of Upper Chalk, Middle Chalk, Upper Greensands, Gault, Lower Greensands, Wealden Beds, Purbeck Beds and Portland Stone that have been subject to complex folding. All the sediments have been tilted vertically, around 45 degrees for Worbarrow and 60 degrees for Mupe. In effect both the cliff sections have been buckled upwards to form a horseshoe shape with the bottom of the horseshoe hidden from sight deep beneath the ground. The cliff sediments have also been twisted horizontally. This is why the Chalk is found at the back of the bay, while the Portland Stone and Purbeck Beds take the brunt of the seas at the front, forming the peninsula of Worbarrow Tout in the east and the Mupe Rocks in the west.
Chalk Cliff Erosion
Erosion of coastal Chalk cliffs is slow. Chalk is relatively hard, and only becomes unstable when the sea has carved a cave into its base, destabilising the weight of cliff above. The sea then has to wash away the cliff fall before the process can start all over again. The milky coloured seawater found at the base of Chalk cliffs, particularly around fresh falls, is evidence of coastal cliff erosion in progress.
The Great Unconformity and The Cretaceous Blanket
The sediments which make up the Jurassic Coastline were deposited in the following order, Triassic, Jurassic and Cretaceous, with the oldest rock, the Triassic sitting at the at the bottom of the pile.
Part way through the Early Cretaceous Period the sea levels dropped and the layers of rock were tilted to the East by earth movements. Overtime the exposed rocks were eroded before sea levels rose again, depositing more Cretaceous sediments.
The combined tilting and erosion explains why the Jurassic Period is completely missing in East Devon and why areas of cliff all along the coastline are capped with Cretaceous rocks which are millions of years younger than the sediments laying directly beneath them.
Coastal Visitor Centre
Lulworth Heritage Coast Centrev
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Interest: MOD Lulworth Firing Range and Walking
MOD Lulworth Firing Range and Walking
The Lulworth Firing Range belongs to the Ministry of Defence. Everything from rifles, machine guns and tanks use the area which stretches along the coastline from Lulworth to Kimmeridge. Red flags fly when the area is in use, gates are locked and wardens patrol the area. There is a range patrol boat to guide shipping away from the danger areas and flying restrictions operate in the airspace overhead. The footpaths are cleared of any unexploded ordnance between the yellow markers, but occasionally unexploded shells can be washed up onto the beach. These are dangerous and should not be touched or moved. Contact the Range Wardens who will arrange the safe disposal of the offending item. It is worth mentioning that it is not uncommon for divers to see unexploded shells on the seabed. These should be left where they are and given a wide berth. The range walks and coast path are open most weekends and some weekdays, but more definite information can be obtained by contacting the Lulworth Firing Range Wardens on 01929 404819.