Mind the Gap!

A 49m wide, 40m deep sinkhole has opened up in the Peak District, Derbyshire, due to an old lead mine in the area. Two other sinkholes have been seen half a mile away in the 1970s, so this isn't a new occurrence. The sinkhole has grown in size by about 10% in the last few days due to the continued bad rain, and it's thought that other sinkholes could open.

Sinkhole (courtesy of the BBC)

The BGS has discussed sinkholes, or dolines, in more detail. There are several different types of sinkhole. Some occur due to dissolution of soluble rock (solution sinkhole), like when limestone dissolves after being hit by acidic water. Others occur where there is a thin amount of loose material on top of soluble rocks, that gets washed into fissures, slowly creating a suffosion sinkhole. If this loose material is cohesive, then the fissures will grow larger before collapsing, causing a drop out sinkhole. Others occur due to the gradual collapse of a cave at depth, causing the overlying rocks and sediment to fall in (collapse sinkhole). If the rocks are not prone to dissolution, then it is termed a caprock sinkhole. The final type of sinkhole is caused by the erosion of weak material due to flowing water, creating voids in sediment.

Types of sinkhole (courtesy of the BGS)

There are several things that can trigger these sinkholes, some of which are human induced. It can just be as simple as gradual dissolution of the surface rocks, however heavy rain and flooding can cause cavities to collapse, along with leaking drainage pipes, burst water mains, irrigation and even emptying a swimming pool. Drought can cause sinkholes too, as it changes the level of the water, causing cavities to collapse. Construction work can also trigger a sinkhole, as it modifies the drainage in the area, and alters the amount of weight on the ground. Mining can also cause sinkholes, by removing water in the area, or removing clay voids, causing them to collapse, such as the one in the Peak District.
In order to deal with sinkholes, proper planning and site investigation must take place before construction work begins, and maintenance of infrastructure must be kept up. The groundwater levels must also be taken into account during development, and drainage systems may need to be put in place.
The map below shows soluble rocks in the UK, but don't think that you can't leave the house any more, it is relatively safe out there, honest!

Soluble rocks in the UK (courtesy of the BGS)