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Because of the hundreds shakes and shimmers through the year Yellowstone is considered one of the most seismically active places on the planet. Even though, the last known eruption occurred more than 70,000 years ago, geologists believe that it may happen again. At the heart of Yellowstone's past, present, and future lies volcanism. Disastrous eruptions occurred here several times in history. Eruptions occurred first, at about 2 million years ago, then 1.2 million years ago, and then 600,000 years ago. The latest, spewed out nearly 240 cubic miles of rubbish. The ash from the eruption spread over the area of 22 western states, it was so deep that it was mined in the 1930's and used to make a cleanser. What is now the park's central portion then collapsed, forming a 28- by 47- mile caldera. The magmatic heat powering those eruptions still powers the park's famous geysers, hot springs, fumaroles, and mud pots.
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