A giant crater in the southeast English county of Surrey has enveloped part of a residential street, causing the county to declare a major incident. Here’s what we know.
What’s going on?
There’s a hole.
A what?
A hole. Actually, two holes.
The first hole appeared on Godstone High Street on Monday night, and grew on Tuesday to 65 feet by 20 feet and 16 feet deep. The second hole on the other side of the road is 16 feet by 16 feet, and 16 feet deep. Since Tuesday, both holes have stabilized and neither are continuing to expand.
What caused this?
The cause is unclear, but geologists have some theories.
The area is built on weakly cemented sandstones, which formed during the Lower Cretaceous period more than 100 million years ago, that can be eroded by running water, Andrew Farrant, a geologist for the British Geological Survey, said in a statement. While this is not usually an issue, a sudden change in the composition of the ground — caused by heavy rainfall or an influx of water from a burst pipe — can trigger a collapse.
In Surrey, a burst water main might have flushed out weak sandstone bedrock beneath the road or caused the collapse of an old, unrecorded sand mine. Or the collapse of a mine roof might have led to the bursting of a water main, said Vanessa Banks, a geologist for the British Geological Survey.
More broadly, the push in Britain to build more houses has meant that more water goes into aging infrastructure, putting more pressure on pipes, she said. Periods of intense rainfall, which are likely to become more common because of climate change, can also put more pressure on the seals of aging pipes, she said.
Is anyone in danger?
No, but people in about 30 properties have had to evacuate, the Surrey County Council said.
“Our house is not secure at all,” one resident who evacuated, Noosh Miri, told the BBC. “At the moment we don’t know the extent of the damage but we do know we won’t be going home for some time.”
