When this supervolcano blows, the entire United States will be impacted. Politics will have little meaning afterwards. Yellowstone's magma chamber is as big as three Lake Michigans combined. The supervolcano may not explode in our lifetime, but the geologic record proves that this supervolcano has erupted approximately every 500,000 years. The last eruption occurred about 640,000 years ago. Therefore, when magma begins to move at Yellowstone, it is wise to pay attention.
By Brian Handwerk
National Geographic News
January 19, 2011
Yellowstone National Park's supervolcano just took a deep "breath," causing miles of ground to rise dramatically, scientists report.
The simmering volcano has produced major eruptions—each a thousand times more powerful than Mount St. Helens's 1980 eruption—three times in the past 2.1 million years. Yellowstone's caldera, which covers a 25- by 37-mile (40- by 60-kilometer) swath of Wyoming, is an ancient crater formed after the last big blast, some 640,000 years ago.
(See "When Yellowstone Explodes" in National Geographic magazine.)
Since then, about 30 smaller eruptions—including one as recent as 70,000 years ago—have filled the caldera with lava and ash, producing the relatively flat landscape we see today.
But beginning in 2004, scientists saw the ground above the caldera rise upward at rates as high as 2.8 inches (7 centimeters) a year. (Related: "Yellowstone Is Rising on Swollen 'Supervolcano.'")
The rate slowed between 2007 and 2010 to a centimeter a year or less. Still, since the start of the swelling, ground levels over the volcano have been raised by as much as 10 inches (25 centimeters) in places.
"It's an extraordinary uplift, because it covers such a large area and the rates are so high," said the University of Utah's Bob Smith, a longtime expert in Yellowstone's volcanism.