Britain suffered from a plague of sink holes due to the recent winter storms, with the British Geological Survey indicating almost a five-fold increase in reported incidents since the storms began.
With 9 sink holes reported between the 1st and 20th February alone, Dr Anthony Cooper, a principle geologist at BGS, suggested that the increase of weather patterns including drought followed by heavy rain are likely to make sink holes a more frequent disaster.
One of the reported sink holes appeared in Ripon, North Yorkshire and has forced several homeowners to be evacuated from their properties, with the extension of one house being almost completely torn from the building.
So what are Sink Holes?
Sink holes can be defined as any hole that is created through erosion and the drainage of water. There are two types of sink hole, cover-subsidence sinkholes which are created slowly over time and cover collapse sink holes which appear suddenly and are the type that we have seen across the country so often these last two months.
Generally, sink holes occur frequently in areas where land consists of soluble bedrock, such as limestone or gypsum which can be dissolved by water.
Cover collapse sink holes occur when cracks form naturally underground and are hollowed out by water erosion, leaving the soil or sediment above. Eventually the soil or sediment situated above the eroded area will no longer be able to support its own weight and as a result will collapse leaving a hole or crater. At times of high rainfall, the ground becomes saturated which speeds erosion and the weight increase often helps trigger these sudden events.
So why the huge increase in reported cases?
Out of the 9 reported cases mentioned above, most of them have occurred in the South East where the bedrock is formed of Soluble Chalk. This area (and much of England) has also suffered one of the wettest winters in recent times. With greater volumes of water dissolving vulnerable bedrock, sinkholes have become a common occurrence.
The cause of sink holes can also be partly because of human activity. A lot of the recent cases have occurred adjacent to man-made constructions, such as houses and roads where rain water has been directed to a particular area in the form of run-off, thereby channelling the fluvial erosion to specific points.
Fortunately, no fatalities were caused by this latest wave of sink holes but with the ability to swallow cars (8 Corvettes were swallowed by one sink hole in Kentucky recently) and destroy family homes – like the sink hole in Ripon – the danger they pose must not be underestimated.
BT/SRJ