As a disastrous mud eruption on Indonesia’s Java Island marks its second anniversary, the unprecedented event continues to stir debate about whether it resulted from an exploratory gas well drilling accident or a distant earthquake and how long it will last. The mud volcano, nicknamed Lusi, has been disgorging mud at a rate of up to 150,000 cubic meters per day. Officials are struggling to contain the effluent within dikes that are regularly breached and built anew farther out.

In November 2006, ground deformation near the volcano ruptured a natural gas pipeline, killing 13 people. Lusi’s mud has engulfed 750 hectares, destroying the homes of more than 30,000 people as well as factories and farms. “Sadly, it’s not about simple technical problems anymore. It’s more [about] economic and social and political problems,” says Satria Bijaksana, a geophysicist at Institut Teknologi Bandung.

Lapindo Brantas, the oil and gas exploration company that operated the ill-starred gas well, and the government have promised compensation to landowners, but it has been slow in coming. Hundreds of families are still living in temporary shelters. In two separate cases, Indonesian courts have ruled the eruption a natural disaster, absolving Lapindo Brantas of liability.

Ivan Valentina Agung, a lawyer for Walhi, an Indonesian environmental group that filed one of the suits, says the group is appealing to a higher court in hopes of getting Lapindo Brantas to take responsibility for environmental rehabilitation.

For scientists, Lusi is an intriguing specimen. A flurry of papers refines previous work on the eruption’s dynamics and offers insights into the evolution of mud volcanoes. “This is a great opportunity. Nobody knows how other mud volcanoes looked when they were first appearing,” says Adriano Mazzini, a geologist at the University of Oslo.

There is general agreement on the sequence of events. On 27 May 2006 at 5:54 a.m. local time, a magnitude-6.3 earthquake struck near Yogyakarta, in central Java. Between 5 and 8 a.m. the following day, Lapindo Brantas’s gas well, which was being drilled 250 kilometers to the east near the town of Sidoarjo, began to flood. Workers shut the well’s blowout preventer to keep the fluid from gushing out the top. They noted that pressure inside the well rose rapidly before gradually subsiding. Early in the morning of 29 May, mud began burbling out of the ground about 150 meters away.

In a February 2007 article in GSA Today, Richard Davies, a geologist at the University of Durham, U.K., and colleagues claimed that the drillers penetrated a porous limestone formation about 2800 meters below the surface, inadvertently tapping into a highly pressurized aquifer. The borehole’s casing didn’t extend deep enough to protect rock from cracking under the pressure when the blowout preventer was shut, he concluded. Water then channeled its way to the surface, bringing mud with it (Science, 2 February 2007, p. 586).

That’s not how Mazzini and his colleagues see it. In the 30 September 2007 issue of Earth and Planetary Science Letters, they argued that the region’s geological structures, pressurized hydrocarbon deposits, common in the region, and a seismic fault created conditions “perfect for a mud volcano.” The only thing missing was a trigger, Mazzini says. The drilling might have contributed, he says, but he believes a more important factor was that the Yogyakarta earthquake reactivated the fault. At roughly the same time Lusi broke, mud also erupted from eight fissures along a 100-kilometer stretch of the fault line. “I don’t think this is a coincidence,” he says.

Global Positioning System (GPS) data and an obvious kink in a rail line show that ground along the fault has shifted up to half a meter since the Yogyakarta earthquake. But Michael Manga, a geologist at the University of California, Berkeley, who has studied how earthquakes trigger distant volcanic eruptions, contends that the quake was too small and too far away from the fault to influence it. In recent decades, he says, “there were many earthquakes that were both closer and bigger and by any measure more likely to have triggered an eruption.”

In a paper published online on 5 June in Earth and Planetary Science Letters, Manga, Davies, and colleagues suggest that the fault is likely to be shifting in response to the movement of vast amounts of material to the surface. The mechanism is not clear. Co-author Rudi Rubiandini, a petroleum engineer at the Institut Teknologi Bandung, says the analysis “makes every other reason [for the eruption] impossible.” Most earth scientists agree that the well must have had some effect, says James Mori, a seismologist at Kyoto University in Japan. But he says researchers can’t determine whether the volcano would have formed without the drilling.

While sympathizing with Lusi’s victims, geologists say they relish the rare opportunity to study a mud volcano’s birth and evolution. GPS and satellite-based interferometric synthetic aperture radar data indicate that the surface near the volcano’s vent is collapsing into a funnel shape, characteristic of sand draining from the top bulb of an hourglass. Davies and colleagues concluded in a paper published online on 21 May in Environmental Geology that between June 2006 and September 2007, the funnel’s center sank at about 4 centimeters per day, which in 3 years would produce a sag of 44 meters. They also report that areas outside the funnel are rising, probably due to movement of the fault.

Scientists are puzzling over other phenomena as well. Since March 2007, the flow has periodically stopped for hours or days only to resume with its previous vigor. The likely explanation, Davies says, is that the weight of mud at the surface is collapsing the vent deep underground. Pressure backs up until it breaks through the blockage. In addition, there have been 88 minieruptions of water and methane where the ground is subsiding. Rubiandini believes the subsidence is cracking open pressurized gas pockets. And along the fault, geysers of water have suddenly shot up in the middle of yards, rice paddies, and even within factories, probably due to the rearrangement of subsurface plumbing.

“The volcano is taking on a life of its own,” Davies says. How long this will go on, he says, is anybody’s guess.

Unstoppable

The mud volcano Lusi is unique in its longevity and the volume of material ejected. It may also be setting records for the number or failed attempts to plug it. Immediately after the 29 May 2006 eruption, Lapindo Brantas., the company whose exploratory drilling, some claim, triggered the eruption, pumped concrete into the well to try to stop the gush of hot, salty water from a subsurface aquifer. When that failed, the company brought in a consultant from Houston, Texas, who directed the drilling of two relief wells intended to intercept the original borehole and pump in high density drilling mud to plug the leak. This effort was abandoned when the wells were short of their target, also, reportedly, because Lapindo ran out of money.

In February 2007, following a proposal from geophysicist Satria Bijaksana and two colleagues from Institut Teknologi Bandung, Lapindo Brantas started dropping into the vent clusters of concrete balls, 20 centimeters and 40 centimeters in diameter, roped together with steel cables. The objective, Bijaksana says, was “to reduce the sheer volume of mud coming out of the vent to a manageable level.” This effort was abandoned after 398 of a planned 1000 clusters had been dropped; a government agency that took over management of the disaster concluded that the balls were having little effect.

The only hope of plugging Lusi is to drill another relief well to plug the original well at a point below where it was breached, says Rudi Rubiandini, a petroleum engineer at Institut Teknologi Bandung. He estimates that the well would cost $70 t0 $100 million. But that is unlikely to happen, he says: “Our government now thinks this is a natural disaster and impossible to kill.”

Dennis Normile