What are the causes of sinkholes?

A massive sinkhole appeared in a high street in Surrey this week.

It first appeared in Godstone High Street on Monday 17 February and grew to at least 20m long by Tuesday. 

But what causes them?

After a devastating sinkhole appeared in northwest China in January 2020, we spoke to geotechnical specialist Dr Clive Edmonds to learn more about what causes them. 

What triggers sinkholes?

Dr Edmonds has studied sinkholes for the past 30 years. 

He's found that the causes range from water to human development. 

Water

"The main trigger for sinkholes is water," said Dr Edmonds.

"In 90% of sinkhole cases, water saturating the ground is the main trigger, known as Karst processes."

"Sinkholes happen when a layer of rock underneath the ground is dissolved by water."

Geology

The geology of the area has a significant role to play in the formation of sinkholes.

"Sinkholes depend on geology," explains Dr Edmonds.

"Some rocks are more soluble than others - salt deposits for instance dissolve more quickly.

"Gypsum for instance is a very soluble rock. Chalk and limestone deposits may take thousands of years to dissolve, but when new cavities occur they can cause spectacular sinkholes."

Humans

"Human development can contribute greatly, especially construction work in urban areas where you may have dense development with roadworks, and so on." says Dr Edmonds.

"The surface becomes impermeable with water collecting over time in drains and sewers - water starts leaking into the ground."

Sinkhole warning signs

Dr Edmonds said that there are sometimes warning signs of a sinkhole. 

"First indicators are dips and depression in the ground surfaces, deepening with tiny cracks in pavements or buildings for instance, leading to buildings showing slight movement," he said.

Tunnelling into water-filled cavities or where water bodies can flow catastrophically into an excavation are particularly hazardous.

"In the UK, any such instances have been caused by small cracks in the ground.

"These lead to the onset of building movement and then a breakdown in the water utilities, or leak of a mains water pipe, or a sewer eventually draining water into the ground."

In the UK, there has been a long history of mining and water abstraction, which in some areas has left a legacy of man-made cavities.

Can you always predict when a sinkhole is going to appear?

The term sinkhole is, in the UK, often extended to cover the collapse of ground into such man-made features.

However, Tony Bracegirdle, senior partner of the Geotechnical Consulting Group, said that there can be very little surface evidence of a sinkhole, which makes predicting a collapse difficult.

"There are seldom warnings in urban areas," said Bracegirdle.

"Although sometimes sinkholes develop slowly to the extent that there's sufficient time to restrict access."

"Sinkholes tend to focus in specific geological and topographic conditions and so the hazard can be reasonably quantified in areas where there is a history of recurring sinkhole activity."

"The most common response in high-risk locations is to design works that are insensitive to potential sinkholes," he said.

 "[Works that] control surface water, and to take additional precautions to limit water loss from drains and services."

First published on 14 January 2020. Updated 19 February 2025.