In 1872, President U. S. Grant signed a bill designating Yellowstone the world’s first national park. At over 2.2 million acres, it is larger than Rhode Island and Delaware combined. Although the park has some beautiful mountains, rivers, lakes and waterfalls (over 100 of them), it is most notable for its thermal features. About 600,000 years ago an enormous volcanic eruption created a 1,300 square mile caldera (crater), one of the world’s largest. By comparison, the one created by the Mount St. Helens eruption was only a couple of square miles. Much of the hole was eventually filled with lava, and the caldera is barely visible today, but the earth’s crust, which is normally 20-30 miles thick, is only 2 miles thick here. This makes for a lot of thermal activity. Yellowstone has over 75% of
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