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To look deep inside an Antarctic volcano, scientist Phil
Kyle and his team have to use a little force.
Researchers spent more than three months installing an array
of seismometers around Mount Erebus to listen to waves of
energy generated by small, controlled blasts from explosives
they buried along its flanks and perimeter. Seismometers
measure and record the size and force of underground energy,
or seismic, waves.
By studying the refracted and reflected seismic waves,
the scientists can map the interior of the volcano, much
as a CT scan images the inside of an object using X-rays.
Kyle, a volcanologist with the New Mexico Institute of
Mining and Technology, has learned much about Erebus in
the last 35 years. But so far, he only has suspicions
of what lies below the magma lake, a pool of molten rock,
visible from the crater rim.
“There have been very few direct studies of a volcano’s
magma chamber,” Kyle said. “What you see in
the textbooks — the long, straight conduit leading
down to a round chamber — probably isn’t at
all what it looks like.”
Instead, Kyle said, what probably exists is a conduit
that leads down to a series of irregularly shaped chambers.
He makes the point with a zigzag of his fingers.
This year’s goal to establish the seismic network
and test the concept hasn’t been an easy one to reach.
Atrocious weather often pinned down the people working
on the 3,796-meter-high volcano and left helicopters on
standby at McMurdo Station for days at a time.
Still, as the season came to a close at the end of January,
the scientists had managed to install 23 of 25 planned
broadband seismic stations around the flanks and summit
that will stay out to record sound waves from distant
earthquakes and the volcano’s own rumblings over
the next year. In addition, the team set up 14 temporary
sensors just to record the explosions, and later recovered
those instruments.
Catherine Snelson, assistant professor of geophysics
at New Mexico Institute of Mining and Technology, is in
charge of the active-source seismic work. She and blasters
from McMurdo Station had managed to set off seven blasts
to start building an image in the upper 2 kilometers of
the volcano, in what they hope will set the stage for
a possible larger campaign in a coming field season.
“We’re going down about 21 kilometers,”
Snelson said. “The emphasis this year is to develop
the technique.”
(Environmental effects from the installation, operation
and removal of the seismic instruments — in addition
to the use of explosive charges on Mount Erebus —
should be less than minor or transitory, according to
an environmental review of the project prior to the beginning
of the season. Following detonation, non-explosive residues
are collected and transported to McMurdo Station for disposal
as waste.)
The seismic waves recorded by the instruments after the
explosions help the scientists infer where areas of heat
and magma are located. Snelson said the velocity of the
waves also says something about the types of rocks and
liquids buried below.
Kyle emphasized that there was no danger of the explosives
creating any sort of reaction in the volcano. “They’re
like little earthquakes,” he said.
The process to create these little earthquakes isn’t
too earth shattering, they said.
Seismometers at crater rim monitor the 'heartbeat'
of the volcano
The process begins with drilling a hole, worked performed
by Jay Kyne from the Ice Core and Drilling Services at
the University of Wisconsin-Madison. Using an ice core-drill,
he made 15-centimeter-wide holes up to 12 meters deep
into the ice, at three locations of interest for the project.
The explosive used by the blasters, led by Marty Reed,
is ammonium nitrate/fuel oil (ANFO), an explosive fertilizer
mix. Snelson said the fertilizer is environmentally safe
and normally stable unless deliberately detonated.
The explosives team placed a small amount of ANFO in
the bottom of each hole to serve as a bed for the detonators
and boosters (that, as the name implies, gives a boost
to ignite the ANFO), then poured several more sacks of
ANFO into the holes, according to Reed.
“The amount of explosives was in relation to the
depth of the holes,” Reed explained. “In some
areas, where rock might be encountered, drilling would
stop — the reason the drilling machine was designed
for cutting through ice and not rock.”
The holes and the blasts have only a negligible and short-lived
impact on Erebus’s environment, and the explosive
work conforms to strict safety standards, according to
National Science Foundation (NSF) officials.
Reed’s team often supports science and construction
projects throughout the summer season. For example, they
work with marine biologists to create holes in sea ice
for scuba diving if the project is too far away from McMurdo
Station to use heavy equipment to drill the holes.
“When we are with geologists, the projects vary
from the seismic work like the current Mount Erebus project
or fracturing siltstone for removing plant and animal
fossils like on Beardmore Glacier,” Reed said.
“The Beardmore Glacier camp was a fantastic adventure
in 2003,” he added. That season, a science team led
by Allan Ashworth found various plant and animal fossils
on Oliver Bluffs and Bill Hammer’s group collected
dinosaurs specimens on Mount Kirkpatrick.
This was the first time the blasters worked on Mount
Erebus, he said. “Just being on a volcano in Antarctica
is unusual; using explosives as a tool for the research
just adds to the novelty,” Reed said.
A short film clip of one detonation recorded a dull thud,
a muffled version of the explosion one hears on a ski
mountain to control avalanches. A small geyser of snow
shot into the air to mark where the team had set the ANFO.
A few whoops of excitement followed by some off-camera
voices.
Snelson said the technique is still a little rough, as
the explosion shouldn’t have disturbed the surface
snow. Instead, the explosion should have been contained
to maximize the seismic energy produced. The team brought
about 850 kilograms of ANFO to Erebus this year. In future
seasons, she said, they plan to use about ten times that
amount — still well below the annual limits dictated
by environmental protocols.
The seismic work itself is not new to how Kyle’s
team monitors the volcano. Several permanent seismometers
sit at the crater rim — though the number was reduced
by one in March 2007 when a “bomb,” a hot rock
launched from the open lava lake, crushed the instrument.
Most of the time, the instruments work passively, picking
up the sound waves from distant earthquakes, or the rumblings
and grumblings of Erebus, what Kyle refers to as “monitoring
the heartbeat of the volcano.”
Tom Wagner, program manager for Earth Sciences in the
Office of Polar Programs at the National Science Foundation
(NSF), said the project will answer a fundamental question
about volcanism — the nature of that deep plumbing
system — that he is surprised hasn’t already
been discovered.
“If you want to understand why [volcanoes] undergo
explosive eruptions or predict when they are going to
erupt, this is the sort of fundamental information that
you need,” he said.
“And it’s profoundly important to do this work
at Erebus because of the lava lake, which is a window
into the plumbing system,” Wagner added. “By
combining all of the information on gas release, heat
exchange, and magma history with the seismology, we have
a chance to develop a picture of how volcanoes work in
way that cannot be done elsewhere on earth.
“This is one of the most exciting projects we have
going on for the next couple of years.”
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Antarctic
Sun
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