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How fast-rising magma contributed to deadly volcano

Magma from the deadly eruption of Irazú in Costa Rica decades ago, recently helped researchers better understand quickly erupting volcanos. Now scientists hope to learn more by investigating other volcanic sites.

By Becky OskinLiveScience / August 1, 2013

Alaska's erupting Pavlof volcano, in the Aleutian Islands, seen in a photo snapped from the International Space Station in May. Earthquakes deep beneath the surface may be driving some fast-moving volcanos, researchers have learned.

NASA Earth Observatory

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Molten rock from Earth's hellishly hot mantle can punch through miles of overlying crust in a matter of months, a new study finds.

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Before the deadly 1963 eruption of Irazú volcano in Costa Rica, magma surged 22 miles (35 kilometers) in about two months, traveling from the mantle to the volcano's shallow magma chamber, researchers report in the Aug. 1 issue of the journal Nature. The evidence comes from geochemical tests on crystals of the mineral olivine from ash erupted in 1963. Layers in the crystals helped re-create the magma's pre-eruption journey.

"We refer to our story as the 'highway from hell,'" said Phillip Ruprecht, lead study author and a volcanologist at Columbia University's Lamont-Doherty Earth Observatory in New York.

The discovery at Irazú helps confirm other clues for high-speed magma ascents, such as deep-seated earthquakes before eruptions at Mount Pinatubo in the Philippines and Iceland's Eyjafjallajökull volcano, the researchers said. Seismic tremors struck near the mantle below Pinatubo and Eyjafjallajökull in the weeks and months before the blasts. And other geochemical tracers in lava also suggest magma could shoot to the surface from the mantle in mere months. But the new study is the first hard evidence of a fast mode in volcanoes, Ruprecht said. [Amazing Images: Volcanoes from Space]

Skipping the stairs

Despite some clues suggesting speedy magma ascents, most models of volcano plumbing were akin to a slow pipe. A volcano's magma chamber fills from the bottom, like a sink filling from its drain. Many pulses of molten rock can pump into the chamber during a volcano's lifetime. Based on geochemical evidence in lava, researchers thought the magma melts would rise a bit, mix together, and then climb a little more, until finally reaching the chamber. The long journey happens over a span of thousands to hundreds of thousands of years.

"It's like going up a set of stairs. Each step is another change," said Adam Kent, a geologist at Oregon State University who was not involved in the study. "By the time you get to the surface, the magma has been changed quite substantially."

But the new study found evidence that magma feeding the 1963 eruption skipped the stairs and took the express elevator to the surface, mixing with other molten rock only at shallow depths, around 6 miles (10 kilometers) below the Earth's surface.

"This is telling us some interesting stuff about what's driving these volcanoes, which is hot stuff coming from deep within the mantle," Kent told LiveScience's OurAmazingPlanet. "The real proof of the pudding would be to find this behavior at many different places," he said.

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