Scattered across the globe are a few active volcanoes with such mighty potential. The notorious Yellowstone Caldera of Yellowstone National Park is one of them, inspiring visions of doom should it erupt. Another was recently discovered near Pompeii, Italy, the
Scattered across the globe are a few active volcanoes with such mighty potential. The notorious Yellowstone Caldera of Yellowstone National Park is one of them, inspiring visions of doom should it erupt. Another was recently discovered near Pompeii, Italy, the Roman town buried by the eruption of Vesuvius two millennia ago. But what is a supervolcano, and how did it get so powerful?
For a volcano to be called "super," it has to have the potential to eject more than 1000 cubic kilometers, or 240 cubic miles, of volcanic material. That is one thousand times greater than any volcanic eruption seen by modern humans. A dead giveaway of a volcano's potential to be super is hidden deep within the Earth's crust, where an enormous chamber of magma forms because of incredible heat (2500 F) rising from the Earth's mantle.
The magma reservoir buried 6 miles beneath Yellowstone is fed, according to computer models, by a 45-mile-wide plume of molten rock from at least 410 miles beneath the Earth's surface. A surge of magma into the chamber causes the pool to swell, like water in a balloon, and pushes the surface of the land above the magma chamber upward. Scientists posit that the magma migrates horizontally to cool and solidify, causing the surface to settle back down. According to geological surveys, the magma chamber beneath Yellowstone has been "breathing" like this for the past 70,000 years without eruption, big or small.
"Our earliest modern data begins in the 1920s when the roads in the park were first surveyed," says Jacob Lowenstern, scientist in charge of the Yellowstone Volcano Observatory. Lowenstern says the ground above the chamber rose about 7 inches between 1976 and 1984 and then dropped about 5.5 inches over the next decade. From 2004 to 2008, the land rose almost 3 inches a year, which is three times greater than ever observed since 1923. For comparison, the flanks of Mount St. Helens swelled 5 feet a day in the months prior to its 1980 eruption.
Lowenstern estimates that Yellowstone's magma chamber has a volume of about 15,000 cubic kilometers, which is greater than the volume of Lake Superior. But most of the magma is not uniform. Some is solid, some of it is viscous, and, at most, about 30 percent is molten. That's why scientists can predict exactly how catastrophic a Yellowstone eruption would be; the chamber would not erupt in its entirety.
Supereruptions of the Past and the Future
Every supereruption leaves behind a telltale token of its occurrence, a sort of "I exploded here" stamp in the ground in the form of a massive cauldron, or caldera. After the supereruption occurs, the land above the emptied magma chamber collapses to form a gigantic crater. The caldera formed after Yellowstone's last supereruption measures 28 by 47 miles. According to the USGS, the surface area and volume of a caldera corresponds to the area and volume loss of the magma chamber, but calderas can change over time.
Forty-seven known supereruptions have plagued the planet, disgorging their contents in regions where Earth's tectonic plates battle for position or at hotspots like Yellowstone where plumes of hot rock surge up from deep within a continent.
The largest known supereruption in the last 25 million years was caused by plates shifting in Lake Toba in Sumatra, Indonesia. This supervolcano erupted 74,000 years ago, ejecting 2800 cubic kilometers of volcanic debris—approximately the volume of Lake Ontario—and plunging the earth into a six-to-10-year volcanic winter. Scientists speculate that this supereruption may have whittled down the human population to a few tens of thousands.
A supereruption in Yellowstone could have similarly dire effects, owing to the sheer volume of magma sequestered in the crust and its volatile history. About 2.1 million years ago, Yellowstone's Island Park Caldera supereruption belched out 2500 times more ash than Mount St. Helens did in 1980. Since then, Yellowstone has belched two more supereruptions, one every 600,000 to 700,000 years. The most recent supereruption was 640,000 years ago.
The Phlegrean Fields volcano near Naples, Italy and the Lake Taupo volcano in New Zealand are two other active volcanoes capable of supereruptions. Other areas suspected of harboring supervolcanoes include Indonesia, the Philippines, Central America, the Andes, Japan, and the Kamchatka Peninsula in eastern Russia.
Beware the Ash
The first image of volcanic mayhem that most people picture is lava—hellish rivers coming down from on high, obliterating all in its path. It's easy to fear lava, but the ash is even more hazardous and travels much farther. A mixture of splintered rock and glass, volcanic ash clogs machinery, kill