Sink Holes

Sink Holes

There is a saying, usually after saying or doing something that you wish you hadn’t, that you “wish the ground would open and swallow you up!”

For some people, this has actually happened, and not from wishing, but from a sinkhole that has appeared in the ground, large enough to swallow people, cars and even buildings.

Commonly, after a wet winter, an increasing amount of sinkholes will appear across Britain.

A sinkhole is usually formed by erosion, caused by the frequent exposure to water. There are two basic types of a sinkhole; a cover-subsidence sinkhole which is created slowly, over time and a cover-collapse sinkhole which will appear suddenly.

Both are usually the result of what is known as the Karst process where acidic water, which is created by rainfall seeping through the soil, absorbing carbon dioxide and reacting with decaying vegetation, causes the erosion and dissolving of the soluble rock layers such as limestone or gypsum, beneath the surface – eventually creating a cavity below the surface.

The soil or sand over the limestone collapses into a sinkhole when it can no longer support the weight above because of the void below. This final collapse of the surface might take anything from a few minutes to several hours.

There are warning signs in urban areas. These include doors and windows failing to close properly, or cracks appearing in the foundations of houses. In some cases ground movement can be detected. But predictions are not easy:

“It can be very difficult to predict collapse because there is very little surface evidence of the features,” says Dr Vanessa Banks, an expert in shallow geohazards and risk at the British Geological Survey.

Different rock types behave in different ways, she adds. The timing of a collapse also depends on the nature of the soil or rock at the surface which forms a “bridge” over the growing cavern below.

“Consolidated deposits such as sandstone will bridge voids until their tensional strength is exceeded, when the rock will fail and collapse into the underlying cavity,” says Banks.

Certain types of ground – such as gravel and sand – are not fixed in place and so more prone to being washed away.

The erosion may take many years but the collapse may be sudden as it depends on a tipping point determined by the material at the surface, Banks says.

Human development can also affect these natural processes.

When people are building a basement, they may need to drain water, explains Banks. This drainage of water can destabilise the soil by washing away smaller particles – like sand – that are necessary to keep larger particles together, increasing the chances of collapse.

Burst water mains or sewage systems also cause many urban sinkholes to happen, regardless of the rock type below. These cause instability in the surrounding area, often giving the impression of a natural sinkhole, says Banks.

Urban development also adds more weight to the surface layer, potentially speeding up the collapse of a sinkhole.

It is crucial to undertake extensive site investigations prior to building work, says Banks.

There are rules and guidelines for the construction industry in the UK that prevent the discharge of water within a minimum of five metres from a house.

But Banks says that concrete urban development on the whole could in fact be “slowing [sinkholes’ natural] formation by restricting this drainage water from seeping through”.

There are more sinkholes in rural environments, she says, primarily because risky areas are typically avoided by urban developers.

In Britain, the BGS (British Geological Survey) says the carboniferous limestone of the Mendip Hills, the north of the South Wales coalfield, the Peak District, the Yorkshire Dales, the northern Pennines and the edges of the Lake District all host well-developed karst landscapes. Karstic features are also common in the UK on the chalk of south-east England, on salt in the centre and north-east of the country, and particularly on the gypsum that underlies parts of eastern and north-eastern England, especially around Ripon and Darlington, and in the Vale of Eden.

Around the world, the process that produces sinkholes has created striking natural features as the hills of Ireland’s western coast, the caves of Slovenia and the pillars of Guilin in China.

In the UK, so far, there have been no deaths attributable solely to naturally formed sinkholes.

But, since extremes of sinkhole-affecting weather such as long periods of drought, followed by spells of unusually heavy and persistent rain are widely predicted to become more frequent as the Earth’s climate changes, it is expected that there will be more sinkholes in the future, posing the question how long is it until a sinkhole consumes not just a car or building but someone?

Conveyancing Data Services

http://www.conveyancingdata.com/

Conveyancing Data Services is a Conveyancing Search Provider which has been created to supply all the necessary information required for a property transaction in a way that suits you and how you choose to work. Our vast industry knowledge and experience of supplying conveyancing information to the legal sector guarantees that we appreciate the importance of providing a totally bespoke service. We know this is the key to our success and this bespoke service is exactly what we provide. Very few of our clients make the same choices. We have devised a system that will save you time, money and aggravation. Our sole aim is to make the task of ordering products easier than ever before. Whichever ordering, payment and delivery method you prefer our Client Services Team have been specifically trained to manage and meet your expectations. They can be contacted on 0118 9690839 or email info@conveyancingdata.com. Contact: Matthew Joy Tel: 0118 9690839 Email: info@conveyancingdata.com Address 4 The Pavilions Ruscombe Business Park Twyford, Reading RG10 9NN

Leave a Reply

Your email address will not be published. Required fields are marked *