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Yellowstone Caldera

Yellowstone’s Active Geology

Yellowstone Caldera
Geologically speaking the Yellowstone region is very active. It’s moving –- part of the ever shifting continental plates. It’s on top of a chamber of molten rock (magma) that rises and falls. In some places the hot lava is only a mile or two from the surface, and it heats groundwater to the point where it explodes into the air -– making geysers. Most things in geology take place very slowly, measured in millions of years. However, in a little more than two million years Yellowstone has exploded three times, among the largest volcanic explosions geologists have ever discovered. The last one was roughly 640,000 years ago, not all that long in geologic time. Since then there have been a few other minor eruptions and many times lava has escaped through cracks in the earth and flowed into the area around Yellowstone. In ‘recent’ times, perhaps as little as 6,000 years ago, there were eruptions that took place under the waters of Yellowstone Lake -– hydrothermal blowouts that formed Mary Bay, and the Indian Pond.

However, while the Yellowstone area is part of one of the world’s largest volcanoes -– a supervolcano –- it often doesn’t look or feel like that to visitors. For one thing, there is no classic volcanic cone-shaped mountain like Mauna Loa, or Mount St. Helens. There is no active crater with red hot lava jetting from it, such as Mauna Kea in Hawaii. Instead there is the gigantic but hardly visible Yellowstone caldera, the basin created by the last great explosion. Part of the basin was almost completely filled by lava, creating unspectacular plateaus, and another part of it became Yellowstone Lake. Most of the Yellowstone volcano is covered by rolling hills, deep forests, big lakes and rivers, and inhabited by thousands of animals. If it weren’t for the geysers and other hydrothermal features, to untrained eyes there would hardly be any reason to suspect volcanic activity. All of which means that Yellowstone is a safe volcano to visit; it’s not going to explode, or erupt lava, or even do much rumbling and grumbling. Not yet anyway and probably not for at least thousands of years. Meanwhile, geologists are monitoring this supervolcano, probing to discover the secrets of how volcanoes work, and measuring to know if changes are coming to Yellowstone’s activity. There will be warning if this giant starts to wake.

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