Indonesian engineers successfully dropped large concrete balls into a fissure Monday to try to stem a gushing mud eruption that has engulfed hundreds of homes and displaced 11,000 people.

Over the next few weeks, authorities plan to drop nearly 1,500 balls, each weighing up to 40 kilograms, into the crater that started spewing mud at a gas drilling field on Java island nine months ago. The team hopes the balls will gradually reduce the mud flow, which is surging out at a rate of up to 126,000 cubic metres of sediment per day.

Indonesian engineers dropped large concrete balls into an erupting mud volcano Monday to reduce the flow of the sediment that has engulfed hundreds of homes, factories and fields and left 11,000 people homeless.
(Trisnadi/Associated Press)

Sixteen balls were dropped into the fissure Monday. Authorities were to monitor the effects of the balls before dropping more Tuesday.

Critics have said they fear the experiment might cause the mud to flow from different points in the gas field.

Mud fissures are fairly common along volatile tectonic belts such as the one running below Indonesia, and in areas where there are rich oil and natural gas deposits. Opinions differ about the cause of the mud flow, but experts agree it could continue for years.

Some scientists suggest the rupture was triggered by faulty gas exploration techniques by operator PT Lapindo Brantas. Other research suggests it is the result of increased seismic activity, with the mud flow starting two days after a major earthquake elsewhere on Java.

Some of the mud is being channelled to the sea, while the rest is being contained behind dams.