Indonesia tries concrete balls to plug mud volcano

Mud volcanoes are fairly common along volatile tectonic belts and in areas rich in oil and natural gas like Indonesia.

But the eruption just outside the city of Surabaya is exceptional because of the sheer volume of mud that has been surging each day from the hole -- enough to fill 50 Olympic-size swimming pools. Twelve villages and 20 factories have been swallowed, with mud-caked roofs and the tops of lamp posts as the only reminders of what once was there.

Some scientists suggest the rupture was triggered by improper drilling at a nearby natural gas site. Other research points to a major earthquake two days before the mud first appeared in a rice field last May .

The ball-dropping operation, which began last month, follows several failed attempts to contain or stop the mud.

Engineers tried building earthen dams to hold back the sludge, but they are about to overflow. The viscosity of the mud hindered efforts to channel it into the sea. A plan to cap the volcano with concrete was abandoned almost immediately as ill-conceived.

Now, engineers are using a pulley system to hoist the beach ball-sized concrete spheres over the crater before dropping them from a height of about two stories. The balls, each weighing about 150 pounds, are chained together in clusters of four.

So far, nearly 150 have been tossed into the abyss, too few to make an impact. The government has given them another five weeks to make a difference or walk away and let the volcano run its course.

Critics say almost everything depends on the shape of the mammoth gullet, believed by the ball-dropping team to resemble a champagne glass, although recent sonar readings indicate its base may be larger than initially thought.

The hope is that the balls will fit snugly at the bottom, "but it is unlikely to be that simple," said Richard Davies, a geologist at Durham University in Britain who has studied the mud volcano, noting that there apparently are several separate vents.