How do you fix a sinkhole?

Families living on this street in Surrey had to leave their homes after a large sinkhole appeared

You may read about sinkholes - holes that open up on the Earth's surface that appear to happen randomly.

In February, families living on a street in Surrey had to be evacuated after a large sinkhole appeared.

But what causes sinkholes, and how can they be prevented?

Newsround spoke to Paul Beetham, a lecturer in civil engineering and specialist in geotechnics at Nottingham Trent University, to fill in the holes in your sinkhole knowledge.

What is a sinkhole?

Sinkholes can cause great damage to towns and cities when they happen in built-up areas, such as this sinkhole in Japan in November 2016

A sinkhole is a big hole that suddenly appears in the ground.

It happens when the ground beneath the surface gets weak or falls apart, and the surface caves into the hole.

Paul says a sinkhole is a bit like holey cheese saying, "you could be walking over a load of voids (holes) and not even notice half the time and it's absolutely fine, because there's a load solid ground over the void."

But how common are sinkholes? And how do you fix them?

What causes a sinkhole?

Sinkholes are not super common in the UK, but when they do form it can be for a number of reasons.

Often it's down to the type of material the ground is made from, but human activity can also be a cause.

"The ones that you're reading about in the news, like in Godstone, these are more likely caused by failures of drains or pipes or things that humans build," Paul explained.

When one of these drains or pipes burst "the flowing water will just wash away the sand, sandy ground or loose ground that was there and over time, that can build up and then suddenly appear as a hole in the ground."

Are some places more likely to get sinkholes?

Florida is at a greater risk of having sinkholes because of the foundations of the land on which the state is built

There are some things that might make an area more likely to get sinkholes, for example the type of ground.

Some ground is more likely to develop sinkholes, for example limestone which is easily eroded by water.

"In Florida they can get some very large sinkholes from dissolving limestone. And because of their climate as well," Paul explains.

"They've got a hotter climate - a bit more of a tropical type of environment, heavy rain and warmth."

How are sinkholes fixed?

The area is evacuated and a drone is used to look at the sinkhole safely

When a sinkhole forms the most important thing is making sure everyone is safe.

Authorities might evacuate any properties nearby until they know how far the sinkhole might spread.

And when it comes to fixing it, first they need to find out the cause.

Paul said: "They might use drones, for example, to fly over and see and safely see without humans having to go near the ground that might be unstable. And then they can use mine cameras, so they can send cameras underground to see how deep a void might go."

The method of fixing a sinkhole might vary, but often authorities will fill them in.

Paul explained that filling them with concrete can work well, with drills filling the holes up to 20 to 30 metres deep. Wow.