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Question: What is a super-volcano?
Answer: The name 'Super-Volcano' is reserved for the volcanic complexes that produce really big eruptions. Long Valley, California is a large collapse structure called a caldera that was produced by a series of eruptions that occurred about 770,000 years ago, and were about 600 times bigger than the 1980 Mt. St. Helen's eruption. The Yellowstone caldera had an eruption 640,000 years ago that was 1000 times bigger than the 1980 Mt. St. Helen's eruption, and an eruption 2.5 million years ago that was 2,500 times bigger. The La Garita Caldera in Colorado is 22 miles wide by 47 miles long and was produced by an eruption 28 million years ago that may have been 5,000 times bigger than the 1980 Mt. St. Helen's eruption. These large calderas form wide depressions that you could easily drive across without realizing that they were, in fact, volcanoes. Although they do not have the classic cone-shape we see in Hollywood volcano disaster movies, the size of their eruptions mark these volcanic centers as 'Super-Volcanoes'. It is hard to imagine the devastation that would occur if such an eruption were to happen today.
Krakatoa Volcano in Indonesia erupted in 1883 and produced an eruption that was 20 times bigger than the 1980 Mt. St. Helen's eruption. This event produced a massive tsunami that killed 36,000 people, and the explosion was heard over 2900 miles away, but it still isn't the biggest historical event. In 1815, the Tambora Volcano in Indonesia produced an eruption more than 100 times bigger than the 1980 Mt. St. Helen's eruption. The exact death toll is unknown, but it was very large. More than 10,000 were killed directly,and as many as 80,000 may have died afterwards from the poor sanitation and starvation that were indirect results of the eruption. Closer to home, the Katmai, Alaska eruption in 1912 was 30 times bigger than the 1980 Mt. St. Helen's eruption, and the Mount Mazama, Oregon eruption in 4600 BC was 50 times bigger. The Katmai eruption produced the 'Valley of 10,000 Smokes' when the hot volcanic ash filled a nearby valley and continued to release steam for the next 20 years. The Mount Mazama eruption, covered an area of 5,000 square miles with more than 6 inches of volcanic ash, and formed a 'Crater Lake' 5 miles wide and 2000 feet deep where the mountain had been. Fortunately, both of these events occurred in areas that were sparsely populated at the time. These events, however, were still only moderate sized volcanic eruptions.
Although you and many readers are too young to remember the eruption of Mt. St. Helen's on May 18th, 1980, it is an event that made a big impression on people of my generation. At 8:32 AM a small earthquake triggered a large landslide on the north side of the mountain. This landslide uncorked the magma chamber that had been slowly rising under the mountain since early March. The sudden release of steam from the top of the magma chamber resulted in a lateral blast that traveled to the north at 600 miles/hr, knocking down and covering over 235 square miles of forest area. Following this lateral blast, the volcano released a vertical eruption column that continued for the next 9 hours, reaching an eruption height of 16 miles and discharging about 35,000 cubic feet of volcanic ash. One of my college classmates, David Johnston, was about 6 miles north of the volcano at a US Geological Survey observation post. He was never found. He and 63 other people were killed by the eruption. Total damage was in excess of 3 billion dollars. The total energy release from this eruption, including the earthquakes, the steam explosions, the landslide, the lateral blast, and the eruption column, totaled about 5 trillion kilowatt hours. This is such a large number, 5 followed by 12 zeros, that it is hard to understand. During the 9-hour eruption, the volcano was producing 250 times more energy than the entire US power generation capacity; it was the equivalent of 1 Hiroshima sized atomic bomb per second for 9 hours; or enough energy to make 100,000 cups of coffee (or hot cocoa) for every man, woman, and child in the US. We were lucky; this was a small eruption.
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