An underground coal fire burning since the Chester A. Arthur administration could be linked to the Marshall Fire in Boulder County, Colorado, late last December, bringing renewed attention to the dangers posed by coal burning underground, the AP reports. At least 259 underground coal mine fires were burning in the U.S. as of last September according to federal data, with possibly thousands more undocumented fires in unmined coal seams. The subterranean fires can be ignited in multiple ways and are often impossible to extinguish because they feed on the oxygen naturally present in coal itself.

Burning coal seams not only emit toxic fumes and cause sinkholes like those that infamously forced the relocation of the entire town of Centralia, Pennsylvania, in 1962, but are becoming a greater potential danger as climate change, caused primarily by the extraction and combustion of fossil fuels, turns the vegetation above them into veritable tinder.

At least two Colorado wildfires in as many decades were started by mine fires that spread to the surface; and the Marshall Fire — the urban firestorm that incinerated more than 1,000 homes and buildings and killed at least one person in late-December 2021 — may have been started by an “impossible to extinguish” mine fire ignited in 1883. Another pair of fires sparked by burning coal reserves this past summer burned more than 170,000 acres of what is now Montana and on and around the Northern Cheyenne Indian Reservation. (AP; Climate Signals background: Marshall Fire)