BioEd Online

For nine months Indonesian officials have been reacting to the torrent of mud that started erupting from a rice paddy in the village of Porong, East Java, with embankments and evacuations. This weekend they began experimenting with a new strategy for controlling the flow.

The hope is that by dropping 300-400-kilogram concrete balls, connected by chains, into the volcano's mouth they can stem the torrent of mud that has so far covered some 450 hectares of land and submerged four villages. Disaster management officials fear thousands more are at risk.

The chained-ball scheme could cut the flow by 75%, according to the three geophysicists at the Bandung Institute of Technology (ITB) who came up with the idea. This would give the disaster team more time to channel the watery mud to a nearby river or come up with other solutions.

To deliver the balls the team has stetched a cable between a crane on the west of the 50-metre-wide hole through which the mud rises and a tower on the east. Once they have been correctly positioned on the cable with a system of pulleys the balls are dropped into the mud from a height of about 5 metres.

Into the unknown

After the first chain was dropped on Saturday the cable snapped, causing a delay, and on Sunday work was hampered by heavy rain. On Monday the team dropped in four more chains.

The team has calculated that the balls will have to make it down 300 metres to do much good. Nylon measuring lines attached to the first chain told them that the balls had gone down 700 metres. "We think the conduit is much bigger than people had expected," says Satria Bijaksana, one of the ITB geophysicists. He would not venture a guess at the actual size. "We'll be able to tell more when we drop more balls."

Sonar readings taken on Saturday suggest that the volcano's gullet is 'T'-shaped, like an old-fashioned champagne glass, with an abrupt narrowing where a more even conic shape had been expected

The team originally planned to drop 1,000 chains, but the national disaster team that commissioned the project has so far built only 374. Bijaksana says he would be surprised to see any major change before they get to 100 chains, and that might take more than a month. "We want to go gradually. We don't want a deadline. Our main concern is that we have a system that we don't really know. We will make small disturbances and then monitor the changes."

"If we feel confident, we could add more. If we lose confidence, we could stop it," says Bijaksana.

Another way out

Measurements of the mud's temperature and other properties have so far shown no change. The all important flow rate is particularly hard to measure, and the disaster team is trying to carve a small channel that might give them a chance to pin it down more precisely.

Some critics have voiced concern that cutting the flow at this opening might just force the pent-up mud to seek some other outlet.

The ball-dumping initiative was delayed for two weeks by heavy rains, which held up the building of the tower that supports one end of the cable. The team was also stuck in a nearby village for one night last week when the access roads were shut down by a demonstration against the government and the oil company that many blame for the eruption.

Although no one has tried to stem the flow of a mud volcano in this way before, something similar was tried, with some success, when the Italian Navy, the US Marines, and the US Navy worked together to save an Italian village from lava flowing from Mount Etna in 1992 (see 'Concrete evidence that volcanoes can be stopped'). In that case, plastic explosives were used to blow dozens of concrete barriers into the vent in the side of the volcano.