Global cooling: What happens if the Iceland volcano blows

USA Today, by Doyle Rice, Contributing: Associated Press

Lava spews out of the Eyjafjallajokull volcano in Iceland on March 21. The small volcano eruption that forced more than 600 people to flee their homes in Iceland over the weekend could set off a larger volcano. (By Fior Kjartansson, AFP/Getty Images)

Watch Live Streaming Iceland Volcano Erupting Video

The potential eruption of Iceland's volcano Katla would likely send the world, including the USA, into an extended deep freeze.

"When Katla went off in the 1700s, the USA suffered a very cold winter," says Gary Hufford, a scientist with the Alaska Region of the National Weather Service. "To the point, the Mississippi River froze just north of New Orleans and the East Coast, especially New England, had an extremely cold winter.

"Depending on a new eruption, Katla could cause some serious weather changes."

Eyjafjallajokull, the Icelandic volcano that has continued to belch lava, ash and steam since first erupting last weekend, isn't the direct problem. It's Katla, the noisier neighbor, that's the concern. If lava flowing from Eyjafjallajokull melts the glaciers that hold down the top of Katla, then Katla could blow its top, pumping gigantic amounts of ash into the atmosphere.

Scientists say history has proven that whenever the Eyjafjallajokull volcano erupts, Katla always follows -- the only question is how soon.

"If it (Eyjafjallajokull) continues to belch, then you worry," says Hufford.

What's key in having volcanic eruptions affect the weather is both the duration of the eruption, and how high the ash gets blasted into the stratosphere, according to Hufford.

For example, he says, Mount Pinatubo pumped ash for two days in 1991, and spewed it 70,000 feet into the stratosphere. This dropped temperatures worldwide about four degrees for about a year.

"When volcanic ash reaches the stratosphere, it remains for a long time," reports Hufford. "The ash becomes a very effective block of the incoming solar radiation, thus cooling the atmosphere's temperatures."

Scientists are continuing to monitor Eyjafjallajokull for signs of further activity.

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