Long term fire.  It turns out there are many very long lasting fires.  I became interested in the way fire moves underground back in 02000 when I saw parts of the Long Now property on fire, and the fire was spreading through the root systems of trees.  Every 5 minutes or so a tree would just appear to spontaneously combust.  That fire eventually blew up in near nuclear proportions (mushroom cloud and everything) and tragically took out a swath of the ancient bristlecones.

Since then I have noted several long term and underground fires (which also  produce massive amount of global CO2).  The one pictured above from Uzbekistan is one of the more photogenic.  I will keep the list below updated as I find more (like I do with the Underground Wonders post), so feel free to make notes of ones you know about in the comments and they will be added.

• Mt Wingen Australia underground coal fire first noted by westerners around 01828, but it is predicted that it has been burning for over 6000 years.
• “Fossil Reactors” are naturally occurring underground fission reactions in Uranium deposits of Oklo Africa, estimated at around 1.7 billion years old.
• “Door to Hell” (pictured above) Near Darvaz in Uzbekistan, burning since ~01972
• Coal mine seam fires, some of these have been burning since the Qing dynasty in China, and the Centralia PA fire has been burning since 01961.
• Some tire fires have lasted several years