Experts warn against ‘hot’ heatwave on south coast

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Experts warn against ‘hot’ heatwave on south coast

Experts are urging the public to be hypervigilant on the south coast beaches as this week s heatwave could cause cliff collapses.

One geologist said that the area seemed to the most vulnerable and beachgoers should take heed of official guidance.

The collapse of Sidmouth cliff in Devon on Monday was the second large landslide along the Jurassic coast in two weeks.

The Dorset council has a warning about beachgoers to take extra precautions, while Rural East Devon police advised people not to walk on the beach east of Sidmouth because the unstable cliffs could fall suddenly.

Dr Vanessa Banks, an engineering geologist with the British Geological Survey, said: "I walk along a beach as a geologist and I am genuinely shocked that people don't appreciate the overhangs above them sometimes." That is because I have the training and other people are looking at rocks for their beauty.

The councils went out of their way to try to communicate with the public and it would be good to see the public engage with the notices and reflect on them. As the temperature continues to climb this week, the BGS is going to issue social media messages asking people to take care.

Banks said that it is important for people to take care of themselves because we can't tell exactly where these incidents are going to occur. They can't tell themselves because the cracks in the cliff top are not visible to the beach user. There was limited research into thermal impact into landsliding, but there was some evidence suggesting an association. The more clay-like components of sediments shrink due to losing moisture during these hot, dry periods, while other rocks expand in the heat, Banks said.

The south coast appeared to be more vulnerable, which could be partly because of weak rocks and the covering of superficial deposits is not so thick This week, at Sidmouth, we had a formation called the Sidmouth mudstone formation, a fairly fine-growing soil or weak rock, which overlays sandstone, again quite weak, she said.

The cliff fall was led by processes from the top of the cliff. She added that the material at the top, this Sidmouth mudstone formation, is weathered and its erosion is enabled perhaps as a result of some slight movement, maybe because of a change in moisture content.

If the current heatwave was followed by intense, heavy rainfall, that could weaken the cliffs, with potential for further rock falls, she said.

The BGS is studying the impact of hot, dry weather on landslides in the context of climate change, she said. The research focused on heavy rainfall and flooding, which had a greater impact on life and infrastructure.

The risk of rockfalls along Dorset's World Heritage coastline is even greater than usual, according to the Dorset council. Heat causes rocks to expand and, particularly during temperature fluctuations, any pre-existing cracks can widen and new cracks can form. This makes cliffs more unstable and rockfalls more likely to happen. The Dorset councillor Ray Bryan, the portfolio holder for Highways, Travel and Environment, said: Rockfalls are entirely unpredictable and can happen at any time, but we do know which conditions make them more likely, and prolonged hot and dry spells are one of them. Anyone visiting the Dorset coast during the heatwave should stay away from the base of cliffs, and if walking along the coast paths keep well away from the edges, he said. You should never ignore a warning sign that they are there for your safety. The council said that there are a number of areas with increased potential for rockfalls, particularly on the cliffs around Seatown, Eype, Burton Bradstock, West Cliff, East Cliff, Mupe Bay, Lulworth and Swanage.