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By
Peter Rejcek
MOUNT EREBUS is famous for its persistent but low-level
activity as the world’s southernmost active volcano.
But last year it threw one of its biggest recorded tantrums
during its last 165 years.
For the second half of 2005, Erebus erupted as much as
six times a day, throwing what volcanologists call “bombs,”
hot rocks, out of the crater and onto the sides of the
3,794-meter-high volcano.
“A bomb hit one of our [geophysical] stations,”
said Phil Kyle, a volcanologist with the New Mexico Institute
of Mining and Technology who leads a team of scientists
and students attempting to find out what makes Erebus
tick.
Last year’s anomalous activity followed about three
years of uncharacteristic silence, according to Kyle.
Eruptions returned in 2004, and by the middle of 2005,
the scientists knew something was up thanks to data received
from a suite of about 10 seismometers located on the volcano,
mostly around the rim, that operate year-round.
Capt. James Ross provided the first historical record
of Erebus (which he named after one of his vessels) when
his log recorded lava flows on the side of the volcano.
Sketches at the time even showed eruptions, Kyle said.
“We’ve not seen anything like that in our time,”
he added, noting that it is hard to determine the exact
level of activity based on Ross’ notes. The only
other time the volcano has kicked up such a storm occurred
in 1984, when Erebus launched bombs measuring 10 meters
wide and slung them as far as 3 kilometers away from the
crater. Kyle said 2005 appears to be the third most volatile
period on record for the volcano, which has been active
for about 1.3 million years.
“Erebus is less active this year than last year,”
he said. “We don’t know why it starts and stops
like this.” But the answers are coming.
Pooling it together
For more than three decades, Kyle and colleagues have
explored Erebus, a “special” volcano with a
number of features that make it particularly appealing
to study.
Topping that list is its permanent lake of molten lava,
only one of three known to exist in the world, Kyle said.
The other two are located in Africa: Erta Ale in Ethiopia
and Nyiragongo in the Democratic Republic of Congo. The
lake is a result of natural convection that continuously
cycles magma from a chamber deeper inside the volcano
to the surface.
“This is a very rare feature in volcanoes. You just
don’t see these lakes,” Kyle said. “It’s
a window into the magma chamber, [and] it can help us
understand what’s going on.”
The 30-meter-wide lake has at least been in existence
since its discovery in 1972 and aerial photographs from
the 1960s indicate it was around before then, Kyle said.
He believes – based on accounts from the heroic age
of exploration – that the lava lake has likely been
percolating for the past century. Explorers like Robert
Falcon Scott and Ernest Shackleton apparently reported
seeing a red glow above the volcano’s cone during
the dark winter months. What they probably saw, Kyle said,
was the reflection of the lava lake on the clouds.
“I think it’s a persistent, long-lived feature.
It varies, and it’s dynamic. … Each year is
different for us,” Kyle explained. “Each year
we don’t know what we’re going to find.”
The lava itself is also rather rare. Most volcanoes contain
basalt lava but the fiery liquid bubbling in Erebus is
phonolite lava. The composition is particularly interesting
because phonolite is more explosive than basalt. Mount
Vesuvius, the infamous volcano that leveled Pompeii in
79 AD, also contained phonolite lava, according to Kyle.
Such a catastrophic explosion from Erebus is extremely
unlikely, however, because the magma column is exposed
and not capped like Vesuvius, so there is no way for pressure
to build. Also, early indications suggest there is less
gas in the Erebus magma, which is the driving force of
violent eruptions.
One of the goals of the team next season will be to discover
more about the volcano’s plumbing, particularly the
magma chamber inside Erebus that feeds the lake and the
conduit that connects the two. The researchers will install
about 25 additional seismometers on the volcano next year.
Seismometers measure and record the size and force of
seismic waves.
By studying seismic waves, the scientists can map the
interior of the volcano, much as a CAT scan images the
inside of an object using X-rays.
“We can use incoming earthquakes from different places
to see what happens as they pass through the volcano,”
Kyle said, adding that the seismic waves produced by eruptions
from the volcano itself will also be helpful for such
imaging. “Hopefully we’ll get a good look at
what’s inside there.”
What a gas
Volcanologists are also interested in learning more about
what comes out of the volcano to understand Erebus’
effects on the atmosphere and environment.
That’s more the specialty of volcanologist Clive
Oppenheimer, from the University of Cambridge, who is
in his fourth straight field season on Erebus. Using an
infrared spectrometer and other instruments, Oppenheimer
has identified the composition of the ever-present gas
plume that billows out of the volcano’s cone.
Like the lava boiling within Erebus, the makeup of the
gases emitted from the volcano is also fairly uncommon.
Evaporated water and carbon dioxide comprise about 99
percent of the gas, approximately in even proportions,
Kyle said. The Antarctic volcano also emits a number of
other gases in minute amounts including sulfur dioxide
and carbon monoxide.
“I don’t think anyone’s measured levels
of carbon monoxide that we’ve seen here,” Kyle
said. “[Erebus is] putting out a gas of very unusual
composition.”
Last year’s spike in activity also revealed a unique
signature in the gas bubbles that exploded at the lake’s
surface, according to Oppenheimer, speaking from the team’s
hut outpost on the flanks of Erebus.
It turns out the proportion of carbon dioxide is much
higher at the point of the explosion. Oppenheimer said
it’s likely that the source of these gas bubbles
is far deeper in the volcano than the gas normally emitted
from the lava lake.
“The geochemistry of the gases is telling us something
about the depth and the plumbing system and where those
gases are coming from,” Oppenheimer said.
In addition, some of the elements in the volcano’s
magma are very volatile and escape in a gas form. These
include elements such as lead, arsenic and mercury. The
scientists believe trace amounts of these elements could
be drifting at least as far as the South Pole, which sits
at a fairly high altitude.
“We can see Erebus in the snow at South Pole,”
Kyle said. “People have seen lead in ice cores.”
Oppenheimer said one challenge is to determine how big
of a natural polluter Erebus is to the Antarctic environment.
He said current research suggests the perpetual output
of certain Erebus gases such as bromine into the troposphere,
the layer of atmosphere closest to the earth, could affect
ozone. (The scientists say the volcano has no effect on
the ozone layer higher up in the stratosphere, where annual
depletion caused by anthropogenic chemicals makes a hole
form over the Antarctic around August.)
“I think it’s likely that Erebus has some kind
of regional impact on the atmosphere, possibly on the
ozone, but it will be another year or two of modeling
to discern that,” Oppenheimer said.
There are a number of questions the scientists want to
answer about the effects of the gas plume, which issues
non-stop from the volcano. Where does the gas plume go?
How does it affect the snow and ice? How long does the
gas stay in the atmosphere?
“Because it’s so clean down here, that stuff
does get spread out, and Erebus does have an impact on
the environment,” Kyle said. “We’re trying
to assess that.”
In the field
A typical field season lasts about four to six weeks,
with the team a mix of scientists and students. This season
is no different, with one undergraduate and three graduate
students from New Mexico Tech along with a fifth student
from the University of Cambridge.
This is Christine Kimball’s second year on Erebus.
A New Mexico Tech graduate student working on her master’s
degree, Kimball said her fieldwork on the volcano has
definitely influenced her future plans.
“It has been a really amazing experience so far,”
Kimball said from the on-site laboratory on the volcano
shortly before Christmas. “Antarctica is really why
I went to graduate school at Tech in the first place to
work with Phil. I think I’d like to continue to work
in Antarctica in the future, and it’s really made
me want to go for that PhD in the future and stay in research.”
Kimball’s specific project involves studying the
geochemistry of the so-called Erebus crystals, a mineral
called anorthoclase, a type of feldspar that consists
of aluminum silicate. The ones ejected out of Erebus from
the lava lake are highly unusual because of their size.
Kimball is studying and collecting the crystals to learn
more about their growth.
“It’s not well understood,” said Kimball,
who plans to finish her thesis this coming summer back
in the United States.
“Erebus is a great training ground for students …
and I’ve made a great effort to bring students down
here,” said Kyle, who estimated at least 20 students
have written their theses on Erebus over the years.
One of the team’s primary missions each season is
to repair and upgrade equipment. Storms packing winds
in excess of 150 kilometers per hour can cause significant
disruptions to year-round observation. The group relies
on wind generators to power equipment during the winter
but just such a storm trashed five of the generators this
past year.
In addition to the seismometers, other instruments include
microphones around the crater rim that detect explosions
and earthquakes as well as high-precision GPS units that
measure any deformation of the volcano. The latter occurs
if additional magma comes into the system, causing the
volcano to swell, a possible indication of a change in
activity and eruptions. So far, the volcanologists have
only detected slight variations, less than 5 millimeters
per year.
“The thing about Erebus is it’s amazingly stable,”
Kyle said. “It’s out there doing its thing with
relatively unchanged behavior since the ’70s.”
The volcano, which bears the name of the son of the Greek
god of Chaos, may be relatively static since scientists
began studying it in earnest 35 years ago, but today’s
technology is helping them change their ideas about its
role in the ecosystem.
“We used to have our hammer banging on the rocks.
Now we have sophisticated instruments. We’ve got
one of the better instrumented volcanoes in the world,”
Kyle noted. “We’re doing front-line science,
where in the past we were doing exploration.”
NSF-funded research in this story: Phil Kyle, New Mexico
Institute of Mining and Technology, www.ees.nmt.edu/Geop/Erebus/erebus.html.
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The
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