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As Yellowstone Bubbles, Experts Are Calm
Aerial view of a rare eruption of Steamboat Geyser, Norris Geyser Basin, Yellowstone National Park. This 1984 picture shows the world's largest concentration of geysers and hot springs, fed by Yellowstone's active volcanic system. This geyser seldom erupts, only at months to year intervals.
(Courtesy of Robert B. Smith)
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There are a couple of dozen active calderas around the world, but the last super-eruption may have been 26,000 years ago, in New Zealand. There has been speculation that the eruption of the Toba caldera on the Indonesian island of Sumatra 74,000 years ago may have caused global climate changes that led to a die-off of most human beings on the planet.
[an error occurred while processing this directive]A report from the U.S. Geological Survey earlier this year tried to calibrate the volcanic hazards at Yellowstone.
"Depending on the nature and magnitude of a particular hazardous event and the particular time and season when it might occur, 70,000 to more than 100,000 persons could be affected; the most violent events could affect a broader region or even continent-wide areas," the USGS concluded.
Among the hazards are hydrothermal explosions, when steam breaks through the surface and forms a crater. In the 126 years since records have been kept at the park, 26 such explosions have been observed. But the same report argued that a super-eruption is essentially not worth worrying about. The magma chamber below Yellowstone is now "largely crystallized mush."
Yellowstone's hot spot is caused by a plume of magma rising through the Earth's mantle. Over the past 16 million years, the North American tectonic plate has been sliding to the west across the plume. The hot spot has, in turn, bubbled up ever farther to the east from a starting point in eastern Oregon. From a geological perspective, Yellowstone is not so much a permanent place on the map as it is a kind of migratory surface feature of the West.
Volcanologists will readily confess that their field is full of unknowns. The geological processes of the Earth are more chaotic than linear. Large calderas are a particular enigma, with no known major eruptions in recorded human history.
"I can't say we can predict specific events at this point," said USGS volcanologist Robert L. Christiansen. "We keep learning."
Jacob Lowenstern, the scientist in charge at Yellowstone Volcano Observatory, said that with new technology, "we're all kind of viewing the patient for the first time."
