Kaboom
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The Agitator
Last December, Matt Yglesias and Blad Plumer noted that we're past due for an eruption of the "supervolcano" that is Yellowstone National Park. That reminded me that several months earlier, I had promised you an excerpt of what such a cataclism might look like. After the break, a description, excerpted from Bill Bryson's wonderful book, A Short History of Nearly Everything.
Yellowstone, it turns out, is a supervolcano. It sits on top of an enormous hot spot, a reservoir of molten rock that rises from at least 125 miles down in the Earth. The heat from the hot spot is what powers all of Yellowstone's vents, geysers, hot springs, and popping mud pots. Beneath the surfaceis a magma chamber that is about forty-five miles across--roughtly the same dimensions as the park--and about eight miles thick at its thickest point. Imagine a pile of TNT about the size of Rhode Island and reaching eight miles into the sky, to about the height of the heighest cirrus clouds, and you have some idea of what visitors to Yellowstone are shuffling around on top of.
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Where the other supervolcanoes tend to bubble away steadily and in a comparatively benign fashion, Yellowstone blows explosively. It doesn't happen often, but when it does you want to stand well back.
Since its first known eruption 16.5 million years ago, it has blown up about a hundred times, but the most recent three eruptions are the ones that get written about. The last eruption was a thousand times greater than that of Mount St. Helens; the one before that was 280 times bigger, and the one before was so big that nobody knows exactly how big it was. It was at least twenty-five hundred times greater than St. Helens, but perhaps eight thousand times more monstrous.
We have absolutely nothing to compare it to. The biggest blast in recent times was that of Krakatau in Indonesia in August 1883, which made a bang that reverberated around the world for nine days, and made water slosh as far away as the English Channel. But if you imagine the volume of material ejected from Krakatau as being about the size of a golf ball, then the biggest of the Yellowstone blasts would be the size of a sphere you could just about hide behind. On this scale, Mount St. Helen's would be no more than a pea.
The Yellowstone eruption of two million years ago put out enough ash to bury New York State to a depth of sixty-seven feet or California to a depth of twenty.
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The ash fall from the last Yellowstone eruption covered all or parts of nineteen western states (plus parts of Canada and Mexico)--nearly the whole of the United States west of the Mississippi.
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It took thousands of workers eight months to clear 1.8 billion tons of debris from the sixteen acres of the World Trade Center in New York. Imagine what it would take to clear Kansas.
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The last supervolcano eruption on Earth was at Toba, in northern Sumatra, seventy-four thousand years ago. No one knows quite how big it was, except that it was a whopper.
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The event, it is thought, may have carried humans right to the brink of extinction, reduing the global population to no more than a few thousand individuals.
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All this was hypothetically interesting until 1973, when an odd occurence made it suddely momentous: water in Yellowstone Lake, in the heart of the park, began to run over the banks at the lake's southern end, flooding a meadow, while at the opposite end of the lake the water mysteriously flowed away. Geologists did a hasty survey and discovered that a large area of the park had developed an ominous bulge. This was lifting up one end of the lake and causing the water to run out at the other, as would happen if you lifted one end of a child's swimming pool. By 1984, the whole central region of the park--several dozen square miles--was more than three feet higher than it had been in 1924, when the park was last fomrally surveyed. Then in 1985, the whole of the central part of the park subsided by eight inches. It now seems to be swelling again.
The geologists realized that only one thing could cause this--a restless magma chamber. Yellowstone wasn't the site of an ancient supervolcano, it was the site of an active one. It was about this time that they were able to work out that the cycle of Yellowstone's eruptions averaged one massive blow every 600,000 years. The last one, interestinggly enough, was 630,000 years ago. Yellowstone, it appears, is due.
Beer, anyone?
Posted by Radley Balko |
