Did you know that, deep below the snowpack during the winter, wildfires can still smolder? It’s pretty rare – but these overwintering fires do happen! Typically, when forest fires are put out, they stay out. They don’t survive cold, wet winters. But in boreal forests of Canada and Alaska, just below the Arctic Circle, some fires travel and persist underground, biding their time until the winter snowpack melts and spring begins. That’s when they reignite on the surface.
The deepest soil layers in the Arctic and sub-Arctic regions of North America and Siberia contain peat, which is rich in organic matter. The smoldering flames can devour that matter, staying alive even when the surrounding temperatures drop to minus 40 degrees Fahrenheit. The consequence of burning peat, though, is that it emits methane, a greenhouse gas with 80 times the warming potential of carbon dioxide.
These types of fires are more frequent after very hot summers in which large fires burned across wide areas. The higher summer temperatures get, the drier the underground vegetation and soil gets. The bigger the fire at the surface, the deeper its flames can penetrate underground in the summer, making it more likely to survive the winter.
The good news is that these types of fires are still pretty rare – and they account for less than 1% total of areas burned. By keeping tracking of summer temperatures and recording where the largest fires were each summer, firefighters might be able to predict and suppress these fires before they fully reignite.