A Brief History of Nearly Everything
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North American (General)Transcript
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chris stone breaker. Reading from a short history of nearly everything by Bill bryson. Chapter 15. Dangerous Beauty In the 1960s while studying the Volcanic history of Yellowstone National Park Bob Christiansen of the United States Geological Survey became puzzled about something that oddly had not troubled anyone before. He couldn't find the park's volcano. It had been known for a long time. The Yellowstone was volcanic in nature. That's what accounted for all its geysers and other steamy features. And the one thing about volcanoes is that they are generally pretty conspicuous, but Christiansen couldn't find the Yellowstone volcano anywhere in particular. What he couldn't find was the structure known as the caldera. Most of us, when we think of volcanoes think of the classic cone shapes of Fuji or Kilimanjaro, which are created when erupting magma accumulates in a symmetrical mound. These conform remarkably quickly. In 1943 at Cary Coutant in Mexico, a farmer was startled to see smoke rising from a patch on his land. In one week he was be the bemused owner of a cone 500 ft high. Within two years it had topped out at almost 1400 ft and was more than half a mile wide Altogether. There are some 10,000 of these intrusively visible volcanoes on earth all but a few 100 of them extinct, but there is a second less celebrated type of volcano that doesn't involve mountain building. These are volcanoes so explosive they that they burst open in a single mighty rupture Leaving behind a vast subsided pit the caldera from the latin word cauldron. Yellowstone obviously was of this second type, but Christiansen couldn't find the caldera anywhere. By coincidence, just at this time, Nasa decided to test some new high altitude cameras by taking photographs of Yellowstone copies of which some thoughtful official passed on to the park authorities on the assumption that they might make a nice blow up for one of the visitor centers. As soon as christians and saw the photos, he realized why he had failed to spot the caldera Virtually the whole park. 2.2 million acres was called Dara. The explosion had left a crater more than 40 miles across, much too huge to be perceived from anywhere at ground level. At some time in the past, Yellowstone must have blown up with a violence far beyond the scale of anything known to humans. Yellowstone, it turns out, is a super volcano. 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 surface is a magma chamber that is about 45 miles across, roughly 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 highest serious claws and you have some idea of what visitors to Yellowstone are shuffling around on top of The pressure that such a pool of magma exerts on the crust above has lifted Yellowstone and about 300 miles of the surrounding territory about 1700 ft higher than they would otherwise be If it blew. The cataclysm is pretty well beyond imagining. According to Professor Bill McGuire of University College London, you wouldn't be able to get within 1000 km of it while it was erupting. The consequences that followed would be even worse. Super plumes of this type on which Yellowstone sits are rather like martini glasses thin on the way up, but spreading out as they near the surface to create vast bowls of unstable magma.