Hot dry weather could trigger dangerous landslides and rockfalls, experts warn

As the UK approaches official drought conditions, experts are warning the public to beware of extra risks from rock falls and landslides.

The prolonged hot and dry weather means cracks in the solid rocks in cliff faces and in the ground, which have long been filled with sediments, soils and clays, are increasingly likely to shift as their moisture content is lost – a process which can result in sudden cracks and failures.

On the Jurassic Coast in Devon, warnings are in place to encourage the public to be cautious close to the cliffs, following a major cliff collapse near Sidmouth.

Two large collapses on Monday and several smaller rockfalls sent enormous clouds of dust and debris across the beach and into the air.

Earlier this week, Sidmouth’s Independent Lifeboat crew posted a warning on Facebook: “Please do not walk on East Beach, there have been multiple cliff falls today – these can happen at any time, on any day and without any warning.

“The best way to stay safe is to keep away,” the crew added.

Similar warnings have also been issued in Dorset.

Vanessa Banks, an engineering geologist at the British Geological Survey, told The Independent the effects of drought, and also heavy rain, differ around the country depending on the type of rock.

“The strata do vary along the south coast and even within the Jurassic coast itself,” she said.

But speaking about the warnings that have been issued she said: “We’re looking at an area that is already subject to marine erosion. This commonly causes erosion at the foot of a cliff, for instance, and that will leave a notch.

“By creating a notch in the cliff, you create a tensional environment above that. The rock is starting to open up a little bit, you get discontinuities developing.”

“Some of these fractures will become filled with sediment, some of which may have clays in them or silts which are quite susceptible to changes in moisture content.”

As well as this process, the heat which rocks are exposed to during extreme weather events can play a different role.

“The rock itself is made up of particles – different types of material – and the thermal regime that is set up [can impact] different minerals within the rock,” Dr Banks said.

During weather extremes the rocks are subject to greater internal stress, which can also increase risks of cracking, and therefore cause rockfalls in some areas.