Scientists reveal how to detect a sinkhole before it swallows you

It's quite a shock when the ground under your feet, your house or your field suddenly disappears leaving a hole. Above, it shows a sink that swallowed a Toyota Camry in 2017

It's quite a shock when the ground under your feet, your house or your field suddenly disappears leaving a hole.

This hole can be tens of meters or more deep, and will eventually lead to a cavity that can extend down hundreds of meters underground.

We call these sinks, and they are a global problem. Sometimes sinkholes are a purely natural phenomenon, but they can also be associated with previous industrial activities, mostly mining.

So, how do scientists like us detect a sink before they appear on the surface?

The geology of the rocks below you is a clue to the possibility of sinks.

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It's quite a shock when the ground under your feet, your house or your field suddenly disappears leaving a hole. Above, it shows a sink that swallowed a Toyota Camry in 2017

It's quite a shock when the ground under your feet, your house or your field suddenly disappears leaving a hole. Above, it shows a sink that swallowed a Toyota Camry in 2017

Limestone is prone to dissolution by groundwater that, over time, can create huge networks of underground caves known as karst.

These can collapse down due to gravity, leading to large surface depressions and damage from subsidence and even total loss of housing.

Historical mine work poorly mapped and recorded in coal, salt, potash, tin and copper often leave holes in the ground. These voids may eventually surface as the roof progressively collapses.

These collapses can be gradual, or they can happen suddenly, with superficial depressions that appear during the night without previous warning.

Such rapid events are often associated with changes in groundwater or during excessive rainfall events.

In a region where all the rocks on the surface are limestone, such as Florida or large parts of China, it is difficult to avoid the risk they pose as there is often little warning.

In densely populated areas, such as the United Kingdom, the lack of available land is leading to the use of abandoned industrial sites, often without adequate prior knowledge or on-the-ground research.

Compensation is available for some types of collapse, such as coal extraction liabilities that are covered by The Coal Authority, but many of the other causes are considered by insurers as "Acts of God". and the coverage is expensive or difficult to obtain.

Sinkhole search

We have both worked on the problem of sinks everywhere, from the gold mines in Australia to the Middle East, particularly in Kuwait and the Dead Sea, and the Bahamas.

We have also been throughout the United Kingdom and Ireland, looking at the mining cavities in South Wales, Yorkshire and the potteries, and collapsing from the medieval chalk robbery to mortar under a major highway near London.

Limestone is prone to dissolution by groundwater that, over time, can create huge networks of underground caves known as karst. These can collapse down due to gravity. A sinkhole opened at the White House earlier this year

Limestone is prone to dissolution by groundwater that, over time, can create huge networks of underground caves known as karst. These can collapse down due to gravity. A sinkhole opened at the White House earlier this year

Limestone is prone to dissolution by groundwater that, over time, can create huge networks of underground caves known as karst. These can collapse down due to gravity. A sinkhole opened at the White House earlier this year

The sinks are a global problem. Sometimes sinkholes are a purely natural phenomenon, but they can also be associated with previous industrial activities, mostly mining. It is believed that the Karst lakes in Croatia were formed from the collapse of the caves

The sinks are a global problem. Sometimes sinkholes are a purely natural phenomenon, but they can also be associated with previous industrial activities, mostly mining. It is believed that the Karst lakes in Croatia were formed from the collapse of the caves

The sinks are a global problem. Sometimes sinkholes are a purely natural phenomenon, but they can also be associated with previous industrial activities, mostly mining. It is believed that the Karst lakes in Croatia were formed from the collapse of the caves

Over the years, we have become experts in measuring Earth's gravity with an ultra-high precision of a few parts in a trillion.

This is known as microgravity. We can use this to detect a cavity, or even a partially filled area with less density than the surrounding rocks, long before any collapse reaches the surface.

Often, they call us after the first collapse has occurred to detect all other possible nearby sinks. Developers should start thinking about this type of work before construction begins.

An additional innovation that we have developed is to carry out what is known as microgravity surveys in 4-D, variable in time and repeated at intervals of months to years.

This allows us to detect changes in gravity, suggesting that the cavities propagate to the surface and potentially become unstable.

We have been observing a problematic section of the Trent and Mersey Canal in Cheshire since 2002 and have repeated the readings on a more or less annual basis.

Historical mine work poorly mapped and recorded in coal, salt, potash, tin and copper often leave holes in the ground. These voids may eventually surface as the roof progressively collapses

Historical mine work poorly mapped and recorded in coal, salt, potash, tin and copper often leave holes in the ground. These voids may eventually surface as the roof progressively collapses

Historical mine work poorly mapped and recorded in coal, salt, potash, tin and copper often leave holes in the ground. These voids may eventually surface as the roof progressively collapses

HOW ARE THE SINKHOLES FORMED?

The sinks are a global problem. Sometimes sinkholes are a purely natural phenomenon, but they can also be associated with previous industrial activities, mostly mining.

Limestone is prone to dissolution by groundwater that, over time, can create huge networks of underground caves known as karst.

These can collapse down due to gravity, leading to large surface depressions and damage from subsidence and even total loss of housing.

Historical mine work poorly mapped and recorded in coal, salt, potash, tin and copper often leave holes in the ground. These voids may eventually surface as the roof progressively collapses.

These collapses can be gradual, or they can happen suddenly, with superficial depressions that appear during the night without previous warning.

Peter Styles and Jamie Pringle for the conversation

During this period, the microgravity results suggest increasing anomalies and that the underlying salt mines that were the reason why the channels were first constructed are becoming less stable.

This may be due to a leak in the channels themselves or to a more frequent heavy rain as the weather changes.

A recent collapse of a section of the same nearby channel in Middlewich, which caused great disruption and almost led to loss of life, has focused our work.

The proposed Phase 2 route of the HS2 is planned to traverse a significant portion of this Cheshire Salt Mine where sinking is very common and the engineering challenges for this high-speed line will be considerable.

We have contributed to a new series of Channel 5 in sinks that has covered this topic and our work in depth.

We hope to provide guidance on how the area should be arranged and where this technique can be used to map other vulnerable areas along this network of water courses.

After all, it is possible to do something about sinks, if they can be detected in time.

The conversation

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