LIUHANGGOU, China - Cai Zhongyong gestures across barren hills, where two stray camels graze on a few brown-green shrubs, and conjures up a medieval vision of hell.
“This used to be a sea of fire. There were flames coming out of holes in the ground,” said the mild-mannered engineer who has devoted his working life to putting out underground infernos.
Puffs of steam still escape from the ground where fire had blazed for over a century and has since been extinguished.
But others are strung out across the coal-mining areas of dry and sunny northern China, many started by careless miners but others sparked naturally by lightning or wildfires.
Often smouldering in coal seams on or just below the surface, they have shaped the landscape of remote western Xinjiang province for millennia and were mentioned by curious 10th century Chinese visitor Wang Yande, says Cai.
Now the government wants to extinguish the fires which are damaging a fragile environment and wasting resources in a rapidly developing country which relies on coal for about three-quarters of its energy.
The smoke clouds already-polluted skies, the fires emit poisonous gases, and can even make the earth cave in - swallowing roads, homes, animals and humans - when weak ash replaces firm coal underground.
Xinjiang is at the heart of the problem
Some 1.8 million tonnes of coal a year were going up in smoke at Liuhuanggou alone each year, and the fire was only put out in 2004 after a four-year, 100 million yuan ($12.4 million) battle.
“Xinjiang probably has the most serious coal fire problem, not just in our country but in the whole world,” Cai said.
In total, the province was losing around 100 million tonnes of coal a year at the time of the last survey in 1996, he added, equivalent to nearly five percent of China's output last year, even though the worst five blazes had been doused.
The government aims to tame all of Xinjiang's fires by 2015 - ambitious given their complexity, and the bitter winters that limit working seasons to 7 or 8 months a year.
Suffocating The Dragon
Extinguishing the buried fires is complicated because the infernos, which reach up to 1000 degrees Celsius, can also travel at up to 2 to 3 metres a month.
“It's like a fire dragon that moves. It has a head, body and tail and it is travelling underground,” said geologist and coal fire expert Huang Wenhui, who thinks the government's timetable may be too optimistic.
“You have to work out which direction it is travelling in if you really want to stop it.”
Seams, or layers of coal, can go on for miles underground, which means they have fuel to burn for decades or centuries.
The land round Liuhuanggou is scattered with red and grey rock that Cai says was formed by coal fires millions of years ago, long before humans reached the area.
The shallowest fires, just on or below the surface, can be tackled by digging out the embers, and slightly deeper ones by excavating a “fire-break” ditch through the coal seam that cuts off the fuel for the blaze.
Those not so easily cut off can be doused with water to bring down surface temperatures - if there is any available.
Mud and water are then pumped down through wells dug into the heart of the fire before it is “buried” again by cutting off the oxygen needed to keep embers glowing.
The gas can be hard to trace, although eventually, all coal fire sites end up covered over to cut off the air.
“Its difficult to work out where it's coming from, particularly in unmapped old mines, which have a lot of corridors,” Huang said.
When underground temperatures fall below a still scalding 70 degrees they are declared extinguished - but they can take decades to cool to completely safe levels.
At Liuhuanggou, pipes still stick out of the ground for engineers to inspect temperatures on a monthly basis.
For now, the land is left to the camels.
“If people start mining again, if oxygen gets in somehow, then it will start burning again,” warns Cai, as the ground behind him puffs steam into the air.
