Like animals, fires can hibernate in the cold, smoldering underground for months on end. Known as holdover or zombie fires, they are not characterized by roaring flames but by plumes of smoke seeping from the ground. How and where do zombie fires originate?
Zombie fires mainly originate in the cool boreal conifer forests found in Canada, Alaska, Northern Europe, or Siberia, where the ground is covered with a thick layer of needles and other vegetation that burns easily.
The soils in these regions are also often very peaty. As the precursor to coal, peat is highly flammable, so when boreal forests go up in flames, it doesn't take much for the fires to spread underground, where they stay alight for a long time. Particularly when the soil is dry.
Even when it snows, the fires tend not to go out, because not enough moisture gets into the soil to extinguish them.
In fact, if there is a lot of peat and other plant residue in the ground, these fires can continue to burn throughout the winter.