An Indonesian "mud volcano" that has oozed sludge for two years is collapsing under its own weight, worsening an environmental disaster that has displaced thousands, a study said Wednesday.

Sudden collapses of up to three metres (9.8 feet) have been recorded at the centre of the volcano in East Java, the study by Durham University and the Bandung Institute of Technology found.

"Such sudden collapses could be the beginning of a caldera -- a large basin-shaped volcanic depression," the institute said in a statement, adding that the caldera could be as much as 146 metres deep.

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©AFP/File/Dwi Narwoko
Gas flows from the crater surrounded by hot mud in Porong, Sidoarjo district. An Indonesian "mud volcano" that has oozed sludge for two years is collapsing under its own weight, worsening an environmental disaster that has displaced thousands, a study said Wednesday.


"(Scientists) propose the subsidence is due to the weight of mud and collapse of rock strata due to the excavation of mud from beneath the surface," it said.

The volcano in Sidoarjo district has been spewing around 60 Olympic swimming pools of mud a day since erupting to life in May 2006 from a gas drilling hole, owned by oil and gas company Lapindo Brantas.

Drilling by Lapindo, owned by the family of billionaire welfare minister Aburizal Bakrie, has been blamed for causing the mud flow, but the company claims an earthquake in the city of Yogyakarta was to blame.

Twelve villages have been affected by the spreading mud and at least 36,000 people have been forced to flee their homes.

The mud volcano, known as "Lusi", has already been an environmental and economic disaster for local people, and study authors say things will get worse as the mud continues to flow and the centre collapses.

"Sidoarjo is a populated region and is collapsing as a result of the birth and growth of Lusi. This could continue to have a significant environmental impact on the surrounding area for years to come," study co-author Richard Davies said.