Do Eternal Cave Fires Really Exist?

Sacred fires, blazes that erupt eternally from mysterious caves plummeting deep, deep into the earth, are a central plot point to my ebook novel, Gettysburg Passage. People have asked, can such a thing really exist? Are you basing your imaginative fiction on something that is not credible? In reality there are documented fires erupting from deep underground that burn indefinitely, perhaps forever. For instance, there are many stories on the web about a fire that burns underground in Centralia, PA. I have attempted to include a few photos of that cave fire but the blogger image loaded is not cooperating. What causes the initial combustion? A fuel source is necessary, like a seam of coal that is exposed near the earth's surface. Ignition may come from many causes, including naturally occurring brush fires from a passing lightning and thunder storm, for example. But not all cave fires are so easily explained and some believe certain fires linked to sacred grounds are a signal from the Creator and maybe an amazing yet risky portal to the unknown.....