Ancient Tsunami Behind Huge Yellowstone Explosion

Jan. 15, 2008 -- Tsunami-like waves created by an earthquake may have triggered the world's largest known hydrothermal explosion some 13,000 years ago, a federal scientist says.

The explosion created the Mary Bay crater that stretches more than one mile across along the north edge of Yellowstone Lake. Debris from the explosion has been found miles away.

Lisa Morgan of the U.S. Geological Survey told a gathering of scientists over the weekend at Mammoth Hot Springs that an earthquake may have displaced more than 77 million cubic feet of water in Yellowstone Lake, creating huge waves that essentially unsealed a capped geothermal system.

Though much has been made in recent years of a possible eruption of Yellowstone's "super volcano," geologists studying the park have long said that the likelihood is greater for a large hydrothermal explosion.

Morgan said that over the last 14,000 years there have been 20 hydrothermal explosions in Yellowstone that mostly left craters bigger than football fields. They resulted in well-known Yellowstone landmarks such as Mary Bay, Turbid Lake and Indian Pond, all near the north edge of Yellowstone Lake.

The explosions happen when hot water just below the surface flashes into steam and breaks through the surface.

Smaller explosions in Yellowstone happen about once every two years but rarely when people are around or in danger, according to a 2007 hazard assessment produced by USGS.