Sinkhole in downtown Guatemala City

THE giant hole in the middle of Guatemala City that swallowed a house and a three-storey building could have been forming for thousands of years.

THE giant hole in the middle of Guatemala City that swallowed a house and a three-storey building could have been forming for thousands of years.

Sinkholes occur when groundwater percolates through layers of rock in the Earth's crust, dissolving it and forming a series of underground caves.

Malcolm Cox, a hydrogeologist at the Queensland University of Technology, said that if the caves became bigger and extended up towards the surface they could make the ground unstable and eventually collapse, swallowing the surface soil - and anything on top of it.

Sinkholes mainly formed where the ground was made up of layered rock, such as limestone, which could be dissolved or washed away with groundwater. Such areas were called karst formations, he said. The Jenolan Caves, three hours' drive from Sydney, are examples of local karst formations.

Bruce Hebblewhite, head of mining engineering at the University of NSW, said it was "highly unlikely" a sinkhole would ever form in NSW.

"There might be very localised areas in this country where we have such limestone but certainly not in urban areas and it's not common," Professor Hebblewhite said.

"If it were to happen it would only be the areas where we have similar geology, which are very few, and we would almost certainly be aware that there was such a development taking place.

"So it's just not on the agenda at all."

Associate Professor Cox said it generally took thousands of years for cracks and caves to form in the Earth's crust.

''But they can be enhanced by removing and pumping out groundwater, or extracting petroleum products in nearby formations,'' he said.

Rainwater seeping into the ground could also erode soluble rocks and further extend the caves. Depressions in the Earth's surface could also occur as a result of the same processes.

Sinkholes could vary in size and depth from a few metres to several hundred metres. They have formed in southern parts of Britain, the US and Europe.

Giant sinkhole swallows three-storey building

The sinkhole in Guatemala City, which formed below the northern part of the capital city, was probably triggered by tropical storm Agatha, which has devastated the region.

''When you get these heavy storms and cyclones that put a lot of water into the drainage system they might wash into these [caves] and erode the top of the cave,'' Associate Professor Cox said. ''[Then] it propagates upwards to the surface and all falls in.''

A local newspaper reported that only one person was killed.

with Georgina Robinson and agencies

Edited from the following sources :

A huge sinkhole caused by Tropical Storm Agatha has opened up in downtown Guatemala City. Photo: AP
http://www.smh.com.au/photogallery/world/giant-sinkhole-swallows-threestorey-building/20100601-wtj7.html

Hole that swallowed a three-storey building

NICKY PHILLIPS June 2, 2010

http://www.smh.com.au/world/hole-that-swallowed-a-threestorey-building-20100601-wvgg.html