The serene natural beauty of Yellowstone National Park belies a violent past.
Yellowstone sits within a caldera 20 miles across, the result of multiple eruptions of a supervolcano. The crater consists of the rubble that subsided into the void left by the magma and ejected pyroclastics after the eruption.
Under the caldera, rising magma has filled a chamber 37 miles long, 18 miles wide and 5 miles deep. The source of the magma is a hot spot, a plume of molten rock rising from Earth’s mantle.
Around 17 million years ago, the Yellowstone hot spot began erupting near what is now the Oregon-Idaho-Nevada border. As the North American tectonic plate drifted southwest, the hot spot fed more than 140 massive flood eruptions along a northeast-trending path that forms Idaho’s Snake River Plain.
Unlike Hawaii, where Earth’s crust is thin, the thick continental crust acts as a lid, allowing the magma chamber to grow to huge proportions as the pressure builds within.
The magma chamber beneath Yellowstone resembles a lumpy banana, with a bulbous end poking up toward the northeast corner of Yellowstone National Park, and the rest tilted gently southwest. Previously, researchers had thought the magma beneath Yellowstone was in separate blobs, not a continuous chamber.
Yellowstone overran the hot spot about 2 million years ago and stalled there, yielding three huge caldera eruptions about 2 million, 1.3 million and 642,000 years ago.
The first two of these eruptions blanketed half of North America with volcanic ash, producing respectfully 2,500 times and 1,000 times more ash than the 1980 eruption of Mount St. Helens. Smaller but still massive eruptions occurred at Yellowstone in between the big blasts and as recently as 70,000 years ago.
Yellowstone’s active periods span thousands of years and feature multiple, weaker eruptions that occur more frequently than previously thought. Even so, the chance of one happening in any given year is less than 1-in-10,000.
The recurrence of cataclysmic eruptions is neither regular nor predictable, but another supervolcano eruption in Yellowstone is inevitable.
Eight other supervolcanoes at various locales are known from the geologic record, and there may be even more as yet undiscovered. A massive eruption occurred in Sumatra 73,000 years ago that released 15 percent more energy than the largest Yellowstone eruption and 20,000 times more than the largest human-made nuclear explosion, or 60 million times the energy of the Hiroshima bomb.
It plunged Earth into a volcanic winter and may have eradicated 60 percent of the human population, leaving as few as 1,000 breeding pairs whose DNA we all carry.
We cannot predict, prevent or prepare for such cataclysms, but we must be humbled by the knowledge that such events have been and will continue to be an important part of the history of our planet on geological time scales.
A full-scale supervolcanic eruption would almost certainly mean the end of our civilization, a sobering and grievous reminder of our tenuous existence and the planet’s blind disregard for us and our ways.
Richard Brill is a professor of science at Honolulu Community College. His column runs on the first and third Fridays of the month. Email questions and comments to brill@hawaii.edu.
