Is the mud volcano slowing?
One month on, Indonesian physicists think their concrete plan might be working.
Physicists in Indonesia are about to embark on the second phase of their effort to smother a mud volcano with chains of concrete balls. The physicists say increased gas emissions from the vent indicate that their plan might be working, although it is too early to tell for certain.
The volcano, in Sidoarjo in East Java, has been spewing watery mud in volumes up to 160,000 cubic metres per day since last May, covering thousands of homes and many factories. There has been great debate there over whether it was caused by a nearby oil-drilling project or an earthquake.
Three geophysicists at the Bandung Institute of Technology, Bagus Nurhandoko, Satria Bijaksana and Umar Fauzi, hatched a plan to drop 1,000 chains, each linking four concrete balls, into the mouth of the volcano (see 'Volcano gets choke chains to slow mud'). As the mud tries to make is way around the balls, it will be sapped of its energy, the physicists reasoned.
A first phase, installing some 374 chains, started in late February and finished yesterday, 26 March. The scientists estimated it would take at least a month from the start of the project before it would have any effect.
There was some excitement last week when the mud flow stopped for more than 30 minutes on 19 March. But this is more likely to be due to a collapse of the walls of the underground conduit that channels the mud, says mud-volcano expert Richard Davies of Durham University, UK. "Perhaps it is undergoing collapse, causing blockage, which cleared once pressure backed up," he says.
Davies, who is sceptical of the chained-ball strategy, says the balls would have a gradual effect if any. "I think Lusi [the mud volcano] will stop by herself," he adds.
Fauzi is also encouraged by an increase in hydrogen-sulphide emission. Hydrogen sulphide concentrations in the air near the volcanic spout have nearly doubled since the balls started being dropped, from 10 parts per million (ppm) to 15-20 ppm; enough to force workers to limit their time on the site to an hour at a time.
"It follows our theory, and it could mean the pressure is decreasing," says Fauzi.
Fauzi and his team had predicted that the energy-sapping friction of the balls would decrease pressure in the surrounding mud. When a fluid containing dissolved gases has its pressure lowered, the gas is released; just like when the top is opened on a bottle of soda. Normally this pressure reduction happens only at the vent of the volcano, says Fauzi, but the addition of the balls increases the area of pressure reduction, increasing the overall gas release.
Now that a month has passed without disaster, the group plans to start the second phase of chain installation; from today they plan to start dropping in another 500 chains. If the rain abates, they say, they can drop up to 60 in a day.
These chains will be the same as the last set, but with an additional coating to keep the hydrogen sulphide from reacting with the concrete. "Otherwise the balls might slowly break down. This will give them a longer lifetime," says Fauzi.
The real test of the method's success will be an accurate measurement of the flow of mud; till now this has mainly been calculated from satellite pictures and estimates of the mud volume, which is not precise enough to spot a small change in the flow rate.
The team is attempting to construct a narrow dirt channel leading from the volcano's mouth to a nearby river, in order to get rid of the mud. This will also allow the flow rate to be measured. But construction has been held up by rainfall, which breaks down the channel walls. "It's been very hard to get quantitative data," says Fauzi.
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