Super volcanic eruptions that blast loads of ash sky-high can change the climate.

Now scientists are finding that the relationship could go both ways — with the climate having an impact on huge volcanic eruptions.

A bone-dry climate, which occurs in periods between ice ages, could make conditions just right for building up enough underground magma to fuel a giant volcanic eruption, said Allen Glazner of the University of North Carolina in Chapel Hill.

He presented this idea here last week at a meeting of the American Geophysical Union.

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Human civilization has never experienced such a catastrophic eruption, which could blanket the state of Texas with soot two feet deep.

The last one was 74,000 years ago, when Mount Toba in Indonesia blew its top in the largest eruption in the past 2 million years.

Even still, with the potential to devastate the Earth's climate with ash and soot, colossal-size eruptions are front and center for researchers who want to find ways of predicting the when, where and how big of such blasts.

Making magma

Beneath the ground, a large enough store of magma must build up to fuel the eruptions.

"It's all got to be underneath the ground in one place, so that when you tap that magma chamber it all comes out at once, or at least in a relatively short period of time, days to weeks," said Jake Lowenstern, the U.S. Geologic Survey's chief scientist at the Yellowstone Volcano Observatory.

[Like Mount Toba, Yellowstone National Park sits atop a giant magma chamber, which slowly fills for hundreds of thousands of years before erupting. It last erupted 640,000 years ago; a similar eruption would devastate a large part of North America.]

Glazner suggested that if more magma gets pumped up from below a volcano than exits at the surface, a super-eruption could result.

One way to change this balance is to turn up the heat, which can occur, he said, during inter-glacial periods when precipitation decreases.

"If you have a system where you're pumping heat in at the bottom and you're cooling it off the top, at the same time you never make a big magma body," Glazner told LiveScience.

When conditions dry out, the cooling effect of water gets turned off. Without cooling, super-size magma chambers can build and ultimately fuel an eruption.

Past blasts

Looking over the history of giant eruptions, Glazner did find that many occurred during inter-glacial periods and in areas with dry climates. He hopes to complete a detailed analysis of the geologic record of eruptions to bolster this theory.

Lowenstern said that Glazner's idea is interesting, but it shouldn't be used to look at any individual volcano.

"So when I look at what Allen was talking about, you're really looking at the effect of one particular factor out of many and how it may be important in the overall behavior of global volcanic systems," Lowenstern said.

Time scales

The trouble with studying super-size eruptions is they don't happen often.

"We've been studying for 30 or 40 years something that is active on hundreds of thousands of years of time scale," Lowenstern said.

"It's kind of like if you were trying to take somebody's pulse and you only left the stethoscope on for a tenth of a second. You might not even get one heartbeat," he added.

Still, researchers are monitoring active and inactive volcanoes to answer their questions.

For instance, they would like to know the size of the underground magma chamber, but imaging techniques are still to crude to show such detail.

"We want to understand what causes those kinds of eruptions, how to recognize when one is coming. And I'm just interested in this idea that the atmosphere and the climate can affect what happens with the style of eruptions," Glazner said.

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