Scientists and drilling experts say they're in disagreement about whether a gas exploration well triggered a fatal mud volcano in Indonesia.

The world's biggest mud volcano killed 13 people and displaced 30,000 more May 29, 2006, in the Porong sub-district of Sidoarjo, East Java. Mud from the volcanic dome destroyed four villages and continues to ooze enough to fill 50 Olympic-size swimming pools every day, researchers at the University of California, Berkeley, said.

The drilling firm Lapindo Brantas has said an earthquake centered 174 miles away triggered the mud volcano, while an international scientific team, including the California researchers, allege it was caused by improper removal of a drill bit.

Both sides presented their findings this week in the journal Marine and Petroleum Geology.

"The disaster was caused by pulling the drill string and drill bit out of the hole while the hole was unstable," said Richard Davies, director of the Durham Energy Institute in England. "This triggered a very large 'kick' in the well, where there is a large influx of water and gas from surrounding rock formations that could not be controlled."