How fast-rising magma contributed to deadly volcano

03.08.2013 01:34

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.
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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.