October 2003 Poll Question:
The odds would seem to be against those ~120 of you who expect to see an eruption at Yellowstone in your lifetime. Yellowstone’s last volcanic eruption formed the rhyolite of the Pitchstone Plateau about 70,000 years ago. Like nearly all of the 30 most recent eruptions on the Yellowstone Plateau, all post-dating the last caldera-forming eruption 640,000 year ago, the Pitchstone Plateau rhyolite flow was non-explosive and produced little if any ash. Averaged over the past 640,000 years, there has been an eruption at Yellowstone every 21,000 years. However, volcanic activity is clearly episodic, with numerous lava flows issued during discrete periods, followed by very long epochs of dormancy. Just when volcanism will resume is unknown.
The most likely geologic hazards at Yellowstone are those that have occurred within historic times. Earthquakes regularly rock the region, including the deadly 7.5 M Hebgen Lake earthquake in 1959. Landslides are a constant battle for Park road crews.
Hydrothermal eruptions frequently occur in the park, resulting in Yellowstone's geysers. Every few years a geyser may erupt too forcefully, hurling bits of rock when boiling water is explosively decompressed due to sudden pressure changes. Rarely, very large hydrothermal explosions create holes in the ground that are thousands of feet across. Between 5 and 10 of these large hydrothermal explosions occurred during the past 14,000 years. As intense as these events must have been, none were followed by extrusion of magma.
This year has been eventful at Yellowstone’s Norris Geyser Basin. Steamboat Geyser, the world’s tallest, erupted three times. New thermal vents grew at Nymph Lake, 3.5 km north of Norris, and increased shallow boiling caused closure of the Back Basin Trail for 3 months. This sort of activity has occurred many times over Yellowstone National Park’s 131 year history, but clearly warrants close attention and vigilant monitoring.
The Yellowstone Volcano Observatory is a partnership between the U.S. Geological Survey, the University of Utah and Yellowstone National Park.