This is a light that never goes out: an eternal flame, hidden behind a waterfall in Erie county, New York, which is a result of natural gas seeping out from underground rocks.
While gas seeps are extremely common, if the flow concentrates into a "macroseep"—a strong concentrated stream of gas—it can ignite and perhaps never go out. This one burns two pounds of gas, most of which is methane, every day, and the flame reaches eight inches in height.
The gas comes from a shale formation about 400 meters below the surface—a result of "natural fracking", where tectonic events have shifted underlying rocks and caused the gas to escape. While it would be a shame to eradicate the flame, the researchers who have studied it rightly point out that it could be tapped for gas—without the need to resort to artificial fracking. [Marine and Petroleum Geolog via New Scientist]