Earth Protect Blog

 An underground coal fire is one of the potential causes investigators are looking into

By John Aguilar

The Denver Post

“It is impossible to extinguish this fire smoke and other gases from the fire emptying themselves through chimneys reaching to the surface in many places, make it look like a group of burning volcanoes,” mine inspector John Mc-Neil, assessing the state of coal mines on Marshall Mesa, 1883.

One hundred thirty-nine years after McNeil wrote those words, Boulder County investigators are looking at the possibility that burning coal under Marshall Mesa — still smoldering nearly a century after the last mine there shuttered — somehow ignited the ground above, sparking last month’s Marshall fire.

It’s just one of several theories that investigators are weighing as a cause of the Dec. 30 fire that, with the help of ferocious winds, swept east into Superior and Louisville and destroyed more than a thousand homes.

Authorities have also been investigating a religious compound near Marshall Mesa, where a passer-by recorded cellphone footage of a shed on fire shortly before evacuation orders were issued. Firefighters had responded to reports of a trash fire on the property, which is occupied by the Twelve Tribes group, less than a week before the Marshall fire exploded.

“The investigation into the cause and origin of the Marshall Fire remains ongoing,” Boulder County Sheriff’s Office spokeswoman Carrie Haverfield wrote in an email to The Denver Post.

“We are investigating any and all potential causes of the fire including coal mines in the area, power lines, human activity, etc.”

But a coal mine-triggered wildfire on the mesa, which sits southeast of Marshall Road and Colorado 93, isn’t without precedent.

In December 2005, authorities concluded that a brush fire that broke out in the popular hiking area was started by a hot vent — which was measured at a toasty 373 degrees — connected to a long-abandoned mine.

While that fire was quickly put out, a similar fire in Glenwood Springs three years earlier took a darker turn.

It’s believed that a burning underground coal seam in West Glenwood started a blaze that, driven by high winds, burned down 29 homes and torched 12,000 acres.

Guillermo Rein, a professor of fire science at Imperial College London who has studied coal seam fires, said there are hundreds of old coal mines on fire worldwide, especially in China and India. There are quite a few in the United States as well, he said, including one that started in the 1960s in Centralia, Pa., that prompted almost the entire town to pick up and leave.

“Colorado has many ongoing coal fires,” Rein said.

“It is hard to detect them because they burn underground releasing little heat and little smoke. The fact is that these fires represent a hazard and carry a low risk, but are not of zero risk.”

The Colorado Division of Reclamation, Mining and Safety in 2018 commissioned an inventory of the state’s 38 high-priority underground fires. The study, done by consulting and engineering firm Tetra Tech, took a close look at the Marshall mine in the fall of that year.

Coal mines operated in the Marshall Mesa area from 1863, before Colorado was a state, until 1939.

“The fire area was inspected, and no signs of fire features or snowmelt were observed,” the report read.

“Additionally, no coal combustion odors were noted during the site visit.”

Tetra Tech determined that the fire’s activity “is very low and thus presents little potential to start a surface fire.” While the firm said the Marshall mine fire “poses limited risk to public safety” and that no abatement was needed at the site, it said due to the fire’s erratic behavior over the years, “it is recommended that it be monitored annually to check for increases in fire activity.”

Tetra didn’t return a request for comment for this story.

Chris Arend, a spokesman for the Colorado Department of Natural Resources, said the state has not made “any additional observations” at the site since 2018.

He said Colorado’s Inactive Mine Reclamation Program within the Division of Reclamation, Mining and Safety “does not have statutory responsibility or mandate to monitor and/or mitigate underground coal mine fires at abandoned sites.”

He said the responsibility to monitor old mines generally falls on the landowner, which in the case of Marshall Mesa is Boulder Open Space and Mountain Parks, which bought the property in the early 1970s.

“The Inactive Mine Reclamation Program receives federal funding that can be used to assist landowners in monitoring and mitigating abandoned coal mine fires, but monitoring by the program is discretionary and generally at the invitation of the landowner who provides DRMS with legal surface access,” Arend said.

Boulder spokeswoman Sarah Huntley sees things differently.

While the city owns the land overlying the Marshall mine, she said, “all issues associated with the reclamation of the former mine site are entirely the province of other governmental agencies.”

“We cooperate with these entities,” she said.

The 2018 mine inventory report noted that workers in 2006 had filled in vents associated with the mine with 275 tons of aggregate material to minimize the potential for another grass fire.

Ten years later, two areas near the mine that had subsided, or sunk down, “were excavated, compacted, and backfilled to natural grade.”

Arend said the best way to extinguish a subterranean fire is to completely excavate and cool it, but “this requires significant resources and is often logistically impossible.”

Rein, the Imperial College London professor, said “smoldering coal is easy to ignite but hard to extinguish.”

“Suppression of a coal fire is very hard and requires plenty of resources and time. It requires a lot of water, like flooding to the top of the galleries of the mine, or sealing completely the access of air into the mine for years or decades until the fire is slowly smothered by lack of oxygen,” he said.

“This is why I say these fires are the most persistent on the planet.” John Aguilar: