Zombie Apocalypse Megastore

A cloud of ash billowing from Puyehue volcano near Osorno in southern Chile, 550 miles south of Santiago, on June 5, 2011. (Claudio Santana/AFP/Getty Images)

Super-volcanoes have probably caused more extinctions than asteroids. But until now it has been thought that these giant volcanoes took thousands of years to form — and would remain trapped beneath the earth’s crust for thousands more years — before having much effect on the planet.

But new research indicates these catastrophic eruptions, possibly thousands of times more powerful than the 1980 eruption of Mount St. Helens, may happen only a few hundred years after the volcanoes form. In other words, they may have a very “short fuse,” according to researchers at Vanderbilt University.

Such an event could make thermonuclear war or global warming seem trivial, spewing untold tons of ash into the atmosphere to block sunlight. The result would be many years of frigid temperatures, wiping out millions of species. A super-volcano that erupted 250 million years ago is now believed to have created the greatest mass extinction the world has ever seen, wiping out up to 95 percent of all plant and animal species. Some renegade scientists believe it was a volcano, not an asteroid, that killed off the dinosaurs 65 million years ago.

But is global suicide lurking right below our feet? Is a super-volcano about to blow its top? Not as far as scientists can tell. Such a volcano results from the accumulation of a giant pool of lava just a few miles below the ground, and there is no known formation anywhere on the planet that is expected to erupt in the immediate future.

Scientists, who could be wrong about that, have thought for decades that once that pool forms, it stays there for thousands of years before erupting. But the new study by geophysicists from Vanderbilt, along with colleagues at the University of Chicago and elsewhere, documents several lines of research showing that the trigger could be pulled quickly, possibly within a few hundred years.

“Our study suggests that when these exceptionally large magma pools form they are ephemeral and cannot exist very long without erupting,” Vanderbilt’s Guilherme Gualda said in releasing the study, published in the journal Public Library of Science ONE.

That research, as well as earlier research that led to a very different conclusion, was based on the formation of crystals in the molten magma that decay at known rates and thus provide a geological clock, dating various events in the history of the volcano.

According to Gualda, previous researchers looked at the decay of zircons, which are common in volcanic rocks, and concluded that the giant magma pools could exist for 100,000 years. But his team looked at the crystallization of quartz, the most abundant mineral in volcanic deposits, and concluded that such a pool would have to erupt in one-tenth of that time, and possibly in only about 500 years.

That makes the threat of super-volcanoes a bit more serious, but there’s no reason to panic.

Gualda’s team studied deposits in the Long Valley Caldera in northeastern California, where a violent eruption blew 150 cubic miles of molten rock into the atmosphere, blanketing much of North America with hot ash and dropping the earth’s surface more than a mile as it sank into the area once occupied by the magma. That was about 760,000 years ago, but all these years later the region still keeps a lot of scientists on the edge of their seats.

The Long Valley geology began misbehaving again in 1978 when a 5.4 earthquake struck six miles southeast of the caldera, suggesting that the volcano might be reasserting itself. In subsequent years that was followed by swarms of small quakes, which are closely associated with pending volcanic eruptions.

A couple of decades ago, trees began dying on nearby Mammoth Mountain from large amounts of carbon dioxide seeping from the magma, according to the U.S. Geological Survey.

Today, the caldera seems to be quieting down, despite several recent bursts of seismic events, but it is probably the most closely watched volcano on the planet. Scientists with the USGS are keeping a close eye on it, monitoring every little belch, and they insist there is no reason for the folks who live in California to be concerned. At least not yet.

Meanwhile, scientists at Oregon State University have been focusing their attention on Yellowstone National Park, where an eruption a couple of million years ago is believed to have been 2,000 times larger than Mount St. Helens. That region also shows constant signs of seismic unrest, and there have been eruptions there several times in the past, according to the Oregon researchers.

Incidentally, researchers at Washington State University in Pullman, who have also been studying Yellowstone, concluded earlier this year that the big eruption 2 million years ago wasn’t one blast, but two, separated by about 6,000 years.

But just because it was split into two parts doesn’t mean it was benign. The Washington researchers believe the first blast was the biggest, and it darkened the sky with ash from California to the Mississippi River.

So super-volcanoes cannot be ignored, and now it seems they can pull the trigger much more quickly than anyone had thought.