St Albans sinkhole
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How sinkholes are formed - in 60 seconds

Sinkholes, like the one which developed in St Albans on Thursday, are large gaping holes which suddenly appear in the ground.

They are often caused by an abnormal amount of water seeping into the ground, but they are difficult to predict.

BBC News has a look at what causes sinkholes to open.

  • 02 Oct 2015
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