'Possible void' three times bigger than previous sinkhole found under St Albans street

The council plans to carry out an 'intrusive' survey as soon as possible

The original sinkhole is currently being filled with foamed concrete (Hertfordshire County Council)

A few weeks after a huge sinkhole opened up on a street in St Albans, the council has said that a "possible void" three times larger than the existing hole could also be lying below the road.

Fontmell Close in St Albans made the news on 1 October, when a 20-metre deep and 10-metre wide hole appeared in the middle of the street, which is built over a 19th Century clay pit.

A survey conducted by Hertfordshire County Council after the sinkhole opened found a "significant anomaly" under the road and homes on the street, and the authorities are now speaking to residents about carrying out "intrusive" surveys to investigate as soon as possible.

The council said there is a "significant amount of missing mass" in the area next to the original hole, and Rob Smith, the council's deputy environment director told the BBC: "We don't know where the centre of the anomaly is but it tells us there is something there that requires further investigation."

It could be six months before the huge void is fixed and the street becomes safe once again.

After the first sinkhole openened, residents were evacuated from their homes. Some have now returned, but the discovery of the new void below the street will be worrying for many.

Sinkholes typically occur in areas where the subterranean rock is porous - water can build up in rocks like limestone, sandstone and chalk, gradually eroding it until it collapses.