A Geological Puzzle Box
In a small grotto behind a 30-foot (9-meter) waterfall, an 8-inch flame burns with surprising geological implications. The gas that feeds it seeps through fractures in the local rock, but its origin story contradicts established models of natural gas formation. The source rock is the Rhinestreet Shale, a layer of black shale formed from marine sediments during the Upper Devonian period, roughly 380 million years ago. This formation sits about 1,300 feet (400 meters) below the surface at the falls.
A 2013 study by researchers from Indiana University and Italy's National Institute of Geophysics and Volcanology revealed the anomaly. Thermogenic gas production, the standard process where heat breaks down carbon in shale, requires rock temperatures of at least 212°F (100°C). The Rhinestreet Shale in this location, however, is much cooler, comparable to a warm cup of tea. This finding suggests the gas is not being "cooked" in the usual way.
The gas composition is also unusual. Although most natural seeps are predominantly methane, the gas at Eternal Flame Falls is about 35% ethane and propane. This makes it a "wet" gas, a composition more commonly associated with hotter, deeper shale deposits. The main seep at the falls releases an estimated one kilogram (2.2 lbs) of methane per day, alongside numerous smaller micro-seeps in the surrounding area.
Catalysis in the Cold
One hypothesis for this strange gas production points to a previously unobserved geological mechanism. Scientists propose that the gas is forming through a low-temperature catalytic process. In this scenario, the shale rock itself acts as a catalyst, breaking down its large organic molecules (kerogen) into smaller gas molecules without the need for intense heat. Tectonic activity in the distant past likely created the faults and fractures in the shale that now allow this gas to travel to the surface.
The shale at the surface, part of the Hanover Shale formation, is also from the Devonian period. The region was once a shallow sea, and the organic-rich black shales are the result of accumulated plankton and other marine life settling on the seafloor. The constant seep of gas through these ancient layers provides a continuous fuel source for the flame. While legends suggest Native Americans of the Seneca Nation may have first lit the flame centuries or even millennia ago, today it is often relit by hikers after being extinguished by wind or water.