Coal seams can burn underground
for years. The fire can start in a mine or be ignited by lightning or
human activity where the coal seam extends above ground.
The dark green
on this satellite image is the area burned by a wildfire near Glenwood
Springs, Colorado, which was started by a coal seam fire. This false-color
image picks up infrared-light wavelengths just beyond the visible
red we see. Healthy vegetation reflects a lot of infrared, shown
on the image as red. Burned or bare ground (or dead vegetation)
appears as green.
|Courtesy of Space
Fire Down Below
Most of the worlds
burning coal seams have been mapped and are monitored. Many start in abandoned
coal mines when sparks ignite coal dust, gas, or trash. They even show
up as abnormal hot areas on satellite images. "Hot spots" include
Pennsylvania, India, Indonesia, and China. This
New York Times article from January 2002 discusses the problem.
mining takes out the coal layer, leaving pillars to hold up the "roof."
If a fire starts and burns through the pillars, the mine can collapse.
Thats what happened to this burning coal seam in Ningxia Province,
China. Read more about it in this
Environmental Health Perspective PDF from the National Institute
of Environmental Health Sciences. (Adobe
Acrobat Reader is required to view the PDF.)
Anupma Prakash, Geophysical Institute, University of Alaska, Fairbanks