From the air the volcano of boiling mud looks like a gigantic stain on the tropical greenery of the island of Java.

At ground level it reeks of toxic gases, the temperature of the mud flow reaches 100C, the earth is in danger of giving way and there could be an explosion at any time.

It is a terrible place to attempt a scientific experiment, but that is what engineers are trying to do with a crane, a pulley, a piece of machinery rigged like a catapult and hundreds of concrete balls.

They are trying to staunch the flow of mud that has churned out for 10 months now — up to 3.5m cubic feet a day of it — submerging five villages, two dozen factories, paddy fields and a highway on the outskirts of Surabaya, Indonesia’s second city.

One by one they have dropped 347 chains of four concrete balls weighing up to 175lb each into the spouting geyser. The aim, said Satria Bijaksana, a geo-physicist, is to block the vent sufficiently to cut the outflow until nature tires of its exertion.

More than 15,000 people have fled their homes and 13 died when a gas pipeline ruptured near a makeshift dam intended to halt the muddy tide.

For Indonesia it is the latest in a series of woes, from the tsunami of 2004 to the eruption of Mount Merapi, a volcano on Java, and the earthquake that wrecked Yogyakarta, the cultural capital, last May.

But this appears to be no natural disaster. A report by researchers led by Professor Richard Davies of Durham University has concluded that it was “almost certainly man-made.” It was just after the Yogyakarta earthquake, less than 200 miles away, that the villagers noticed the stench of rotten eggs around the site of a nearby natural gas drilling rig.

Unknown to them, the British experts believe, a drill had ruptured a layer of earth 9,000ft below the surface, releasing hot water under high pressure. First a trickle, then a torrent of foul sludge erupted from the site. Superstitious locals feared the spirits of the Javanese universe had been angered. For their part, scientists thought the cause was an aftershock from Yogyakarta.

PT Lapindo Brantas, the gas prospecting company controlled by the family of Indonesia’s powerful welfare minister, Aburizal Bakrie, denied negligence. It paid for temporary dams to block the mud and offered relief to poor local people.

As the months went by, the mud engulfed farms and factories. Crops were ruined and workers were laid off. People who lost their homes are living in abandoned warehouses on handouts of £15 a month.

More than 1,000 patients reported to clinics with breathing difficulties, burning sensations and flaking skin. Doctors supplied by the gas company at first told them it was “stress”, local people said. Later, medical staff realised toxic gases, including methane and hydrogen sulphide, were poisoning the atmosphere.

Indonesia’s environment watchdog estimated that clean-up costs could exceed £150m, a huge sum for a poor country. Public dismay turned to anger at the company. That was reinforced when the British-led geological team suggested human error, not the Yogyakarta earthquake, was the likely cause.

“Such an earthquake would be too small and too far away to cause such an eruption,” said Davies. “Our scientific paper proposes that the well was probably the trigger for the eruption, because it drilled into highly pressurised rocks, while having some of the borehole unprotected by steel casing. This caused these unprotected rocks to fracture.”

Tremendous forces underground then drove mud to the surface. In simple terms, said Davies, it was “a blow-out”.

Davies is sceptical about the attempts to seal the vent. He believes it is impossible to gauge the size correctly and thinks the concrete balls may drop uselessly into the morass. He terms it a “David and Goliath” exercise.

Environmentalists are calling for the company to be prosecuted. Yusuf Kalla, the country’s vice-president, believes the firm should bear the costs but has not supported legal action. The government prefers to talk about solving the problem. Rachmat Witoelar, the environment minister, said the latest scheme is to cleanse the liquid and pump it into the sea. This suggestion, too, has set off protests.

While the politicians and businessmen wrangle, nature may give them plenty of time in which to debate the issue.

According to Davies, the disaster is similar to a blow-out caused by drilling off Brunei in 1979. The oil company concerned had to drill 20 wells to relieve the subterranean pressure and it was many years before the eruption stopped.

Additional reporting: Dewi Loveard, Jakarta

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