Looking out across the vast vista of steaming mud, Rene Nijenhuis had a feeling the volcano wasn’t going to stop any time soon.
A coordinator with the UN’s Environmental Emergency Section, Nijenhuis was dispatched to Sidoarjo, Indonesia, after a mud volcano began erupting there, seemingly out of nowhere, on 29 May 2006. Five million litres of hot slurry was spewing out each day and smothering everything in the vicinity. Thousands were forced to flee their homes and villages. The mud gobbled up thousands of acres of farmland, highways, schools and factories.
Worse, no one knew why it was happening. Now, more than six months later, the first scientific study is blaming Lapindo Brantas, an oil company that had been drilling just 200 metres from where the volcano’s main vent appeared. This seems to justify the Indonesian government’s decision to hold the company responsible for most of the costs related to the disaster, which have since spiralled to nearly $500 million. Meanwhile, Lusi – the local people’s name for the volcano – continues erupting apace, and no one seems sure how to dispose of the mud without causing an ecological disaster.
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A team led by Richard Davies of the University of Durham, UK, is arguing that drilling was indeed the cause of the eruption. The researchers found that conditions in the rocks and water-rich sediments beneath Sidoarjo may have been ripe for a rare drilling catastrophe known as a subsurface blowout, in turn creating Lusi.
Much of Earth’s hydrocarbons are stored in rock that is rich in water and organic matter. Besides being ideal for the formation of large reservoirs of oil and gas, this type of geology can also be quite unstable. Waterlogged layers of mud, sand and limestone have a tendency to flow and squeeze like toothpaste rather than fracture.
In order to drill safely in these areas, technicians must carefully encase the boreholes in steel at regular intervals, to ensure that the surrounding layers don’t ooze out. In the case of Sidoarjo, Davies says, “They had drilled 1.7 kilometres below their last casing, which is a reasonably large distance, but not uncommon.”
Based on a rough knowledge of the local geology, Davies believes the drilling company pierced a layer of water-rich limestone at a depth of about 3 kilometres. The water in the limestone shot up the borehole and entered into the fractures in layers of muddy rock at a shallower depth, probably right near the bottom of the steel casing. The force of water at a pressure of hundreds of atmospheres tore into the mud, mixing with it before breaking through to the surface to create the mud volcano. “In hindsight, they probably should’ve put more casing in place,” says Davies. “But hindsight is a wonderful thing, and you can’t rule out that it wouldn’t have happened anyway.”
To support their theory, Davies and colleagues cite two similar, well-documented blowouts that occurred during oil and gas exploration off the coast of Brunei in the 1970s. The latter and bigger of the two, in 1979, poured huge volumes of mud into the sea and left a gash in the ocean floor over a kilometre long. It took 20 years to stop the eruptions from that blowout.
Davies’s team is the first to draw a scientific conclusion about Lusi’s origins (GSA Today, vol 17, p 4), but not everyone is convinced that they are right. “There is a lot of speculation in this paper,” says Adriano Mazzini of the University of Oslo in Norway, who visited Sidoarjo in October 2006 and is preparing his own study based on data and samples he collected. “They assume that there was drilling into over-pressured limestone, but there’s no evidence of that.”
Mazzini believes that Davies’s theory is largely circumstantial, resting mostly on the fact that Lusi appeared just 200 metres from a drilling platform. “It’s a remarkable coincidence, this is true. But let’s not forget that [such geologies] are a primary target around the world for oil and gas companies,” Mazzini says. “I’m not saying that they are wrong, but it’s easy to find alternative explanations.” Among the other potential culprits is a major earthquake that struck 200 kilometres away two days before.
Everyone does at least agree on one point: there is no way of telling when the eruption might end. The fact that the flow of watery mud has gone on for eight months suggests Lusi is drawing on a vast aquifer, says Richard Swarbrick, managing director of GeoPressure Technology in Durham, UK. “This tells us that Lusi has a very efficient and well-connected reservoir,” he says. “It must be tapping an enormous volume, but unless you know what that connected volume is, you have no way of knowing how long it will keep going.”
Whenever it does stop, there could be a grave new danger to anyone on the surface. Swarbrick says geological evidence from past events shows that when an eruption ends, the ground can collapse, at times catastrophically. “Based on how much sedimentary material has been coming out of Lusi, I predict there must be a cavern on the order of tens to hundreds of metres in vertical space. When pressure in the cavern falls below a certain point, we could see a collapse of that magnitude.”
“Geological evidence shows that when an eruption eventually ends, the ground can collapse, at times catastrophically”
That’s not the only worry, however. Although earthen dams have been built to contain some of the flow, there is still the long-term issue of what to do with the mud itself. Nijenhuis has raised serious concerns about the potential hazards. In late July he drafted a UN report in which he revealed the local authorities’ myriad potential plans for the muck, which ranged from flushing it out to sea to using it as a building material, or even spreading it on agricultural land.
To determine how safe such actions might be, members of the UN team sent to Sidoarjo worked with local authorities to run a battery of tests on the mud, looking for everything from heavy metals to radiation.
The results revealed the mud is essentially non-toxic – it would be safe to use in bricks for dwellings and didn’t pose a pollution hazard. It is, however, extremely salty, with a salinity akin to that of seawater. If the mud is spread over cropland, Nijenhuis’s report says, “the crop will be severely affected because the concentration of sodium will exceed the coping capacity of the vegetation”.
Flushing such a salty substance into the nearby river would be similarly catastrophic, effectively eradicating freshwater life with a combination of a rapid change in salinity and a huge influx of muddy sediment.
“Flushing such a salty substance into the nearby river would effectively eradicate all freshwater life in it”
Worse still, when that sediment does reach coastal seawater, it will “rapidly cover the sea bottom and eradicate the existing benthic organisms and disturb the whole food network”, the UN report says. This could have devastating effects on local marine life and the fishing communities who depend on it for their livelihoods.
Nevertheless, that’s exactly the plan the authorities have settled on. “My understanding is that the government has [decided] to channel the mud into the river, and then the sea,” says Nijenhuis.
This may seem like a terrible idea, but as Lusi erupts unabated, homes and factories that have so far been spared from the mud are in danger of going under. “With 5 million litres a day of new material, we can assume that the situation will be worsening in terms of land area covered by mud,” Nijenhuis says. “Extension and expansion of the holding ponds around the volcano will be necessary.”
But even holding ponds won’t last forever. Diverting the mud out to sea may be the only way to minimise further destruction.
