Sinkholes: How do they occur and can they be prevented?

27 February 2025 by: Macleod Simmonds

Sinkholes have moved to the forefront of the news recently due to a 20 metre sinkhole emerging in Godstone, Surrey last week and a second one later opening on the other side of the street. Residents were evacuated from their houses and work is happening around the clock to manage the site. But how do sinkholes occur and can they be prevented?

Firstly, what is a sinkhole?

A sinkhole, is a hole in the ground, caused by erosion or some form of collapse of the earth’s surface layer. They can be small or large enough to be a danger to buildings, cars and humans. One of the most well-known sinkholes in the UK, occurred in 2014 when a 15 foot crater opened on the M2 in Kent. Macleod Simmonds in fact worked on the investigation of this sinkhole.

How do sinkholes occur?

There are two types of sinkhole. One forms when the roof of a cave collapses and exposes the underground cavern. The second type forms when water dissolves the rock underneath soil and creates an underground chasm. Without rock to support it, the soil layer collapses and creates a hole on the surface. In the case of Godstone, news reports suggest that it is probably the second type caused by a burst water main.

What causes a sinkhole?

Sinkholes can occur from both natural and human causes.

Natural causes include: 

• Rainwater seeping into the ground which slowly dissolves soluble rock creating underground voids.
• Underground erosion and water flow: Water movement under the surface can wash away sediment, weakening the ground above.
• Heavy rainfall and flooding: Sudden and heavy rainfall can accelerate erosion and subsequently cause the ground to collapse.

Human-led causes include:

• Groundwater pumping: Excessive water extraction from underneath the surface can destabilise underground rock layers.
• Construction and drilling from initiatives such as excavation, mining and infrastructure development can cause the ground to weaken.
• Water leaking from pipes or poor drainage can erode the soil, leading to sudden collapses.

Manmade sinkholes are often created when city development compromises the structural integrity of underlying rock. Roads, buildings, and other types of construction may cause water to collect in certain areas and wash away the supporting rock layer (especially at low sea levels and after a heavy rainfall).

Is it possible to predict the occurrence of a sinkhole? Can they be prevented?

There are sometimes measures that can be taken to detect the possibility of a sinkhole but often these are not straightforward.

In the case of a highway sinkhole like Godstone, there is equipment that can scan large carriageways networks at traffic speeds looking for potential voids, without the need to close roads or put in diversions. Over the last few years we have been perfecting the combination of the industry-leading towed HDAGPR (High Density Array Ground Probing Radar) solution by Kontur and our own bespoke methodology. Deploying the system in live traffic, at traffic speeds, will allow a fast initial assessment to be undertaken, with the results being used to direct a more intensive investigation. Detecting the location and extents of large voids beneath your carriageway network can allow preventative remedial works to be undertaken before the situation becomes an incident.

Sinkholes don’t just occur on roads

Sinkholes can also occur on construction sites, in forests and natural areas and on farmland and fields. At Macleod Simmonds we offer accurate and reliable geophysical surveys both over and underground. Using the latest technology and software, we provide you with accurate data on any anomalies that lay beneath the ground and make recommendations on action required.

If you have any questions around detecting sinkholes or what to do if one emerges, then please get in touch.