Here are some pictures of, arguably, the world's most famous mine fire: Centralia, Pennsylvania.

   Snow--melted by the heat of the underground fire---on some days, one can see small vents of steam from this area.

   Venting valley:

   Sinkhole, anyone? This sinkhole, at the western end of the "hot" (that is, near the surface) region of the fire, is almost surrealistically deep--at well over seventy feet.  Taking into consideration the fact that I have seen that it has been partially filled in with concrete, etc. at least three times over the years, it absolutely boggles the mind to think of how much coal has been consumed to cause that much subsidence.

   Venting valleys:

   A closer look:

   Subsidence, anyone? -Several years ago, this area was approximately level--or at least on a gentle incline.

More fire! Fire!! FIRE!!!!'s.  Um. -Sorry about that.  :)