Wednesday, June 21, 2017 The Nugget Newspaper, Sisters, Oregon
9
Analyzing magma temps may help in forecasting eruptions
By Mark Floyd
Guest Contributor
CORVALLIS — Although
volcanic eruptions are often
quite hazardous, scientists
have been unable to pinpoint
the processes leading up to
major eruptions – and one
important limitation has been
a lack of knowledge about
the temperature history of the
magma.
A new study analyzed
crystals of the mineral zir-
con – zirconium silicate – in
magma from an eruption in
the Taupo Volcanic Zone in
New Zealand about 700 years
ago to determine the magma’s
history. The analysis shows
the magma went through a
comparatively “cool” period
for thousands of years before
heating up. Once magma tem-
peratures reached 750 degrees
Celsius, it was a short amount
of time – decades or less –
before an eruption occurred.
This pattern of long-term
crystal storage in near-solid
magma, punctuated by rapid
heating, is applicable to many
other volcanoes around the
world, the researchers say, and
may begin to help scientists
recognize when a volcano is
heading toward an eruptive
phase.
Results of the research,
which was supported by the
National Science Foundation,
are being reported this week
in Science.
“Mobility in magma is a
function of temperature, and
most of the time when it’s
sitting there in the Earth’s
crust under the volcano it’s
cool,” said Adam Kent, an
Oregon State University
geologist and co-author on
the study. “Of course, cool is
a relative description since
it’s still some 650 degrees
(Celsius). I wouldn’t put my
finger on it.
“But to erupt onto the
Earth’s surface magma needs
to heat up so it can be runny
enough to be squeezed along
cracks in the Earth and pushed
up to the surface. At lower
temperatures, the magma is
too crystal-rich and viscous to
move. It’s like trying to spread
cold peanut butter onto a piece
of bread. It takes higher tem-
peratures to get things mov-
ing – and then our data show
it’s only a period of years or
decades before it erupts.”
Kent said the Taupo
magma system has similari-
ties to many volcanoes around
the world, including the
Cascade Range in the Pacific
Northwest of the United
States. A past study by Kent
and his colleagues using a
different approach found that
Mount Hood in Oregon also
spent most of its history in a
cold, rigid state before mov-
ing rapidly into an eruptive
phase.
This new study adds more
certainty to the method and
provides a new tool to apply
this work to other volcanoes,
the researchers say.
The key to honing in on
these long-term geologic pro-
cesses is understanding the
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volcanoes’ thermal or tem-
perature history, according to
the researchers. Past studies
began making inroads into
understanding the history of
magma temperatures, but they
relied on trying to reconcile
data from a sample containing
many thousands of individual
crystals.
Using zircon crystals,
which can be dated through
analyzing the decay of ura-
nium and thorium, adds more
resolution, or precision, to the
process. The crystals are like a
“black box” flight recorder for
studying volcanic eruptions,
according to Kari Cooper of
the University of California,
Davis, corresponding author
on the study.
“Instead of trying to piece
together what happened from
the wreckage,” Cooper said,
“the crystals can tell us what
was going on while they were
below the surface, including
the runup to an eruption.”
Zircon crystals occur in
magma from many volcanoes,
and the new technique will
have wide applications to vol-
canoes along the ring of fire
– the belt of volcanoes that
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and elsewhere.
“It removes some uncer-
tainty and gives us a great
new tool to go back and look
at other volcanoes,” Kent said.
The finding also suggests
that if many volcanoes store
their magma in this relatively
cold state, recognizing volca-
noes where warm and mobile
magma is present may help
researchers find volcanoes
in the early throes of pro-
ducing future eruptions. The
technology to monitor vol-
canoes using seismic waves
and other remote techniques
is improving all the time, the
researchers said.
The Science study was led
by Allison Rubin and Cooper
of the University of California
at Davis. Other research-
ers included Christy Till and
Maitrayee Bose of Arizona
State University; Fidel Costa,
Nanyang Technological
University of Singapore;
Darren Gravley and Jim
Cole of the University of
Canterbury in New Zealand;
and Chad Deering, Michigan
Technological University.
Kent is on the faculty of
the College of Earth, Ocean,
and Atmospheric Sciences at
Oregon State.
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