Sinkholes

It was reported today that the man who disappeared into a sinkhole that opened beneath his house (Link to BBC news story) has not been found and the search for his body has been called off (Another Linky).

This sad news leads us to ask a number of questions....

What is a sinkhole?
Are they common occurences?
How do they form?
How to avoid disappearing down one!

Sinkholes are a natural feature generally found in limestone landscapes (also called Karst Scenery) and formed by the ersoion of the limestone rock by water - usually to allow a channel for water to disappear underground.
They do form in other circumstances, but not as frequently, and are most common in Limestone.

There is some useful information about the formation of Sinkholes here: Formation of Sinkholes

As weak acids in the groundwater cause the dissolution of the Calcium Carbonates in the Limestone it creates cavities underground (hence why cavers and potholing fans really like limestone!). This, combined with surface water seeping through cracks in the limestone from above, causes the roof of these caves to collapse, creating a sinkhole or swallow hole. These have been known to make whole rivers disappear or open up huge craters in the surface. Many of these are harmless and even picturesque...

...other less so....


So, how do you avoid falling in one? Don't live in a house built on Limestone of course!!