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.”
What other havoc has the hole wreaked?
Traffic has been diverted from the road, the main road in the village. A car is teetering on the edge of the second, smaller hole, and the owner hasn’t been able to move it.
Another resident, Josh Neame, told the BBC that he slept in his car on Monday night after the hole first appeared.
What are they doing about the hole?
They’d like to fill it.
The site is currently being tested by structural experts, and more permanent repairs will happen once it is deemed safe, the Surrey Council said.
How long will repairs take?
Probably months, said Matt Furniss, the Surrey County councilor responsible for highways.
Displaced residents may be able to move back sooner than that, but the timeline is unclear, he said. “We cannot give a definitive date at this point,” he said. Over the last few days, residents have been able to return home for brief visits to collect personal belongings.
Are holes like these common?
Sinkholes, formed by the dissolution of limestone or other soluble rocks, are common in certain areas, such as near Mammoth Cave National Park in Kentucky, and in parts of Florida. But sinkholes in Britain are usually small and tend to occur in rural locations.
Periodically, new holes form in busier areas in Britain. In December, a hole in Wales opened up in the driveway of a past winner of the reality-TV show Love Island, Liam Reardon, according to local media.
Heavy rainfall can trigger the collapse of old mine shafts or infrastructure, though these cases are not technically sinkholes because the crater is not formed by the dissolution of soluble rocks, according to the British Geological Survey.
Still, people should not be worried, Dr. Banks said. Residences are generally not allowed to be built on areas where abandoned mines are known to have existed. In instances where holes have occurred, houses have been built above medieval mines that had not been recorded.