Some 1,500 concrete balls have been dropped into mouth of mud volcano

PORONG, East Java (AP): For nine months, a gaping hole in the ground has spit out a biblical-scale torrent of hot, black mud, swallowing thousands of homes outside Indonesia's second-largest city and attracting amazed geologists from around the world.

Most say the flow is unstoppable, but Indonesian experts refuse to listen and have recently begun carrying out a scheme straight from a Hollywood movie: dropping nearly 1,500 concrete balls into the mouth of the mud volcano.

"We know lots of people think this is a crazy idea," said Satria Bijaksana, one of three geologists behind the US$130 million (euro99 million) plan aimed at reducing the sludge spew by up to 70 percent. "But we think it will work."

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 surging from the hole each day - enough to fill 50 Olympic-sized swimming pools.

Twelve villages and 20 factories have been swallowed, with mud-caked roofs and the lamppost tops 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 in May 2006.

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 mud's viscosity 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 beachball-sized concrete spheres over the crater before dropping them from a height of about two stories. The balls, each weighing about 70 kilograms (150 pounds), are chained together in clustersof four.

So far, nearly 150 have been tossed into the abyss - too few to make a real impact.

The government has given the plan another five weeks to make a difference, or walk away and let the volcano run its course.