History of Yellowstone’s Supervolcano

The area in and around Yellowstone National Park has seen tremendous volcanic activity in its past. Three giant eruptions have occurred between 2.1 million and 640,000 years ago. The most recent eruption formed the Yellowstone caldera. Since then, the park has seen roughly 80 mostly non-explosive eruptions. Some of these events were about the size of the 1991 Pinatubo eruption in the Philippines. The most “recent” of these smaller events occurred in the Pitchstone Plateau, located in the Bechler and Fall River drainages, 70,000 years ago.

So are we do for another volcanic event in the near future? Scientists from the United States Geological Survey say no. They guess that 15 to 20 giant eruptions have occurred along the Yellowstone hotspot in the past 16.5 million years. Looking over data from the past 2.1 million years, large eruptions only occur once every 600,000 to 800,000 years.

When the volcanoes do blow their tops, it’s a cataclysmic event. Scientists estimate that the three caldera-forming eruptions that happened between 2.1 million and 640,000 years ago were 6,000, 700, and 2,500 times bigger than Mt. St. Helens’ 1980 eruption in Washington State. Together, the eruptions would have expelled enough ash and lava to fill the Grand Canyon.

Researchers also estimate that volcanic ash covered a significant portion of North America’s western half during these eruptions. Those living within 200 miles of Yellowstone would have been in ash up to mid-calf. Individuals living farther away on the continent would still have been dusted with a few inches of the volcanic debris. With wind-swept sulfur aerosol and extremely light ash particles breezing from continent to continent, the effects were felt around the world, likely resulting in a “notable” temperature decrease around the world.

http://volcanoes.usgs.gov/volcanoes/yellowstone/yellowstone_sub_page_54.html