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How to Super-Size a Volcanic Eruption

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Athena Nike
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« on: August 07, 2009, 01:18:40 pm »

How to Super-Size a Volcanic Eruption

By Jeanna Bryner
LiveScience Staff Writer
posted: 22 December 2006
11:18 am ET



SAN FRANCISCO—

Super 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.



Human civilization has never experienced such a catastrophic eruption, which could blanket the state of Texas with soot two feet deep, for about 74,000 years. That’s when Mount Toba in Indonesia blew its top making history as the largest eruption in the last 2 million years.



Even still, with the potential to devastate Earth, 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.



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, U.S. Geologic Survey’s chief scientist of the Yellowstone Volcano Observatory.



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 if 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.


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.




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.

http://www.livescience.com/forcesofnature/061222_super_volcanoes.html

http://whyfiles.org/091beach/5.html

ourselves, here's the new view. Most of the ice sheet rests on land that's below sea level. At a point called the "grounding line" it starts floating, thus displacing its own weight in water, so the important question is to locate the grounding line. And as it turns out, the line may not move much because the flow of the ice streams seems to be restrained by friction against rocks at the bottom and sides rather than the ice shelf. The streams, says Bentley, "don't particularly care whether there is an ice shelf there or not." So if the ice shelf melts, the flow of the streams should not change appreciably.

And since the volume added to the ocean depends on how much ice moves from land to water -- as determined by the grounding line -- the upshot seems to be relative stability. "The ice streams do not appear to be susceptible to the kind of unstable retreat once envisaged," says Bentley. "Their flow is largely insensitive to the presence of the ice shelf so the grounding line would remain the same."

Instead of possibly collapsing in 100 years, as was considered possible 10 years ago, Bentley says the West Antarctic Ice Sheet is more likely to collapse -- if at all -- in perhaps 5,000 years at the soonest.
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