On 24 July 2012, the BGS Landslide Response Team received reports of a large rock fall on the Jurassic Coast at Burton Bradstock in Dorset.
Tragically, 22-year-old Charlotte Blackman from Derbyshire was killed in the incident. The public have been advised to stay away from the cliffs.
It was reported that approximately 400 tons of rock fell in two rock-fall events approximately 20 minutes apart at around 12:30.
- Have British cliffs become more prone to landslides?
The Guardian, 25 July 2012 - Woman feared dead after cliff crashes down to coastal path. The Independent, 25 July 2012
- Couple cheat death by seconds as they watch 300 ton cliff landslide just feet away. The Daily Mail, 19 February 2012
The BGS Landslide Response Team carried out a survey of the site, including a LiDAR survey, on 25 July 2012. Data collected from this survey is logged in the BGS National Landslide Database NLD 18684/1
3D image of failed cliff at Burton Bradstock generated from a LiDAR, laser scanner, survey undertaken by BGS.
The landslide
The BGS Landslide Response Team carry out a LiDAR survey of the Burton Bradstock rock fall landslide of 24 July 2012.
On 25 July 2012, the BGS Landslide Response Team waiting for access to the beach to carry out a survey of the landslide.
The Burton Bradstock rock fall landslide of 24 July 2012.
The BGS Landslide Response Team carry out a LiDAR survey of the Burton Bradstock rock fall landslide of 24 July 2012.
The failure was controlled and constrained by a combination of factors:
- Discontinuities
- Joints and fractures within cliff run vertically and parallel to the cliff face enabling wedge-shaped sections of cliff to fall
- Coastal erosion and weathering
- coastal erosion and weathering of the cliff face are a continual natural process
- the sea is eroding the base of the cliff (undercutting), removing support for the rocks above
- the processes of weathering weakens the cliff, making it more susceptible to failure
- Recent wet weather has added more water into the cliff from above such that grain support is weakened in the Bridport Sand Formation (see Geology below) thereby increasing the likelihood of a landslide occurring.
The rock fall deposit was 30 m long, 20 m wide and 10 m high, which ran out over a gravel beach.
Geology
The geology of the cliffs at Burton Bradstock comprise the Bridport Sand Formation, overlain by the Inferior Oolite Group, overlain by Fuller’s Earth.
Geology of Burton Bradstock area.
The Bridport Sand Formation at Burton Bradstock showing stronger and weaker beds. BGS Photo P005794 taken in 1972.
The cliffs at Burton Bradstock mostly comprise the Bridport Sand Formation, a grey, brownish (weathering to a yellow colour), micaceous silt and fine-grained sandstone with stronger sandstone beds occurring irregularly throughout the succession, typically every metre or so. These stronger sandstone beds are more resistant to weathering so protrude from the cliff face as in the photograph (above right).
The Bridport Sand Formation is approximately 180 million years old and is at its thickest in the Burton Bradstock area, forming the 40-metre-high cliffs seen at the coast. It is a weak to moderately strong sandstone that becomes weaker when wet. Most of the landslide deposit was composed of the Bridport Sand Formation with blocks up to 2 m3 in the landslide debris.
Above this is a three-metre bed of limestone from the Inferior Oolite Group that forms a cap at the top of the cliff. This is a stronger material than the Bridport Sand Formation and, consequently, blocks 2 m x 2 m x 0.5 m were seen in the landslide debris.
Above this is a bed of Fuller’s Earth, a calcareous mudstone forming shallow mudflows cascading down parts of the cliff.
The yellow sandstone cliffs between Freshwater Bay and Hive Beach that are shaped by erosion processes, including landslides. Taken 25 July 2012.
Eroding piles of rock debris along the base of the Jurassic sandstone cliffs at Burton Bradstock are telling signs of continual erosion by landslides. Taken 25 July 2012.
Access to the beach where the fatal landslide occurred is restricted while geologists assess the immediate danger. Taken 25 July 2012.
The British Geological Surveys’ Landslide Response Team map the collapsed cliff from a safe distance using a LiDAR, laser, scanner. Taken 25 July 2012.
The British Geological Surveys’ Landslide Response Team map the collapsed cliff from a safe distance using a LiDAR, laser, scanner. Taken 25 July 2012.
The presence of wide open cracks in cliff face provides a natural warning sign that cliffs may be unstable and potentially dangerous. Taken 25 July 2012.
Fallen blocks of fossil rich Jurassic limestone litter the beach along the World Heritage Jurassic Coast and attract fossil hunters. The public should exercise caution when standing under or at the top of cliffs and are advised to abide warning signs. Taken 25 July 2012.
The 24th July rock fall at Burton Bradstock is a tragic reminder that the UK coastline is a dynamic and constantly changing part of our natural environment. Taken 25 July 2012.
The British Geological Surveys’ initial findings suggest the recent heavy rain was a contributing factor that caused the rock fall at Burton Bradstock. Taken 25 July 2012.
Wide cracks are visible in the rock face and leave unsupported blocks of rock free to fall. Taken 25 July 2012.
Wide cracks are visible in the rock face and leave unsupported blocks of rock free to fall. Taken 25 July 2012.
Sections of the South Coast Path have been temporarily closed to allow geologists to assess the hazards. Ground cracks along cliff edges may indicate danger of instability and should not be approached. Taken 26 July 2012.
A view of the rock debris left by the recent rock fall. Debris eroded from cliffs naturally replenishes the beach sand making coastal landslides an integral part of the coastal environment. Taken 26 July 2012.
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