The coldest place on Earth is also one of the rare spots
where a roiling lava lake offers a window into the heart of a
volcano.
At erebus volcano in Antarctica, a long-lived lava lake puffs
steam and launches lava bombs at scientists who scale its slopes,
hoping to unravel the mysteries of how volcanoes work. (Lava bombs
are flying blobs of molten rock.)
"We think lava lakes are really the top of a magma chamber, so by
studying lava lakes we can see what's happening in the guts of the
volcano," said Philip Kyle, a volcanologist at New Mexico Tech in
Socorro, who has visited Erebus since the late 1960s.
Erebus has been continuously active since as early as the 1970s.
For more than 40 years, researchers like Kyle have climbed its
12,450-foot-tall (3,794 meters) peak during the brief summer,
installing a battery of monitoring equipment that transforms Erebus
into one of the most intensely watched volcanoes in the
world.
In the early decades, scientists gathered just a few precious
weeks' worth of data each summer at Erebus. Now, despite the harsh
climate, everything from earthquake monitors to infrared cameras
perch on the volcano year-round. Instruments also track the
swelling and sinking of the volcano's surface, snooping on magma
pulsing underground; listen to infrasound (sound below
the range of human hearing); and sniff gases escaping into the
air.
The dragon's breath
One of the remarkable discoveries to come from this long encampment
is how regularly the lava lake huffs and churns, like a sleeping
dragon. "I like to say Erebus is breathing, though I've been told
off because Erebus can only breathe out," Kyle said.
Kyle's collaborator, Clive Oppenheimer, a volcanologist at the
University of Cambridge, first noticed the lake's reliable pattern
several years ago, from measuring its never-ending gas prume.
The total amount of gas — mostly an equal measure of carbon dioxide
and water, with a little sulfur dioxide and hydrogen chloride —
rises and falls in a 10-minute-long cycle. The composition of the
gas also switches on the same cycle.
But the brief summer research season meant scientists weren't sure
if the phenomenon occurred only on their watch. Perhaps the dragon
awoke in winter.
Now, with year-round equipment, Erebus investigators have proved
the cycle persists year-round, varying between five and 18 minutes
since 2004, according to a study to be published June 2014 in the
journal.
"The behavior has stayed remarkably constant, which is actually
quite unusual for volcanoes," said Nial Peters, lead study author
and a geophysicist at the University of Cambridge in the United
Kingdom.
The new study also reports other intriguing behavior in the
bubbling lake. For instance, the lava heaves in concert with its
10-minute gas cycle, its surface rising and falling by about 6 to
10 feet (2 to 3 m), Peters said. And lava cooling on the lake
surface cracks and flows outward at a speed that matches the
fluctuating gases. "Think of the lake as a bowl sitting on top of a
pipe, and as fresh batches of magma come up into the bottom they
rise up and spread out," Peters told Live Science's Our Amazing
Planet. "That's what we see in the velocity flow outward from the
center of the lake. It looks like a thick, treacly liquid, which is
gradually convecting."
A rare view
Lava lakes are rare — there are only four long-lived lakes on
Earth, because the volcano must continuously supply lava to the
surface. There are lakes at Erebus, Hawaii's Kilauea volcano,
Ethiopia's Erta Ale volcano, and Nyiragongo volcano in the
Democratic Republic of the Congo.
Erebus volcano's magma is a rare type called phonolite, up to 100
times more viscous than the basalt at Kilauea in Hawaii and Erta
Ale in Ethiopia. Though Erebus is the only
active volcano with phonolite lava, its twin is
Kilimanjaro in the East African Rift, Kyle said. Both are
steep-sided, cone-shaped phonolite volcanoes rising from rifts,
where the Earth's crust is stretching apart. Looming up from Ross
Island, Erebus is visible from McMurdo research station and New
Zealand's Scott Base.
The long-term observations at Erebus volcano's lava lake are among
the only rigorous studies of these valuable windows into magmatic
systems, said Matt Patrick, a volcanologist with the U.S.
Geological Survey's Hawaii Volcano Observatory, who was not
involved in the study.
"The Peters paper represents a big step in understanding active
lava lakes, in large part due to the uniquely detailed observations
they have made of the lava lake activity," Patrick said.
How it works
With their bounty of data, the members of the Erebus team are now
moving toward their next big goal: explaining how the volcano
works.
"That's the $64,000 dollar question," Kyle said of the oddly
predictable plumbing.
Here's what might cause the steady exhalations. Think of blobs
rising and falling in a lava lamp. Now put those blobs in an
underground pipe that feeds the lava lake from a deeply buried
magma chamber. Lava moves up and down the pipe — a flow and
counterflow similar to a lava lamp, according to a model in a
separate study to be published in the same issue of the journal
Earth and Planetary Science Letters.
"The physics of what's going on are fairly different, but it's an
easy analogy," said Peters, who is co-author on the "lava lamp"
study. "Batches of fresh magma come in as blobs, not as a
continuous stream."
But just like a real body, this "breathing" comes from a different
part of the volcano than its burping eruptions. Erebus erupts
when a large gas emerge and burst in the lake,
splattering lava on the surrounding slopes. Some of the volcano's
lava bombs are nearly bus-size.
At Erebus, these belches have a different composition than the
gases that ebb and flow every 10 minutes, researchers discovered.
The investigators think this difference means that the
bomb-launching bubbles come from deeper in the volcano.
"It looks like the two behaviors are very decoupled from each
other," Peters said. The gas cycling continues even when eruptions
suddenly lower the lava lake level, he noted.
Computer modeling of the upper and lower volcanic
plumbing will help explain this strange set of behaviors and
provide insight into the inner workings of other volcanoes, Peters
said.
But there's a hurdle.
"Basically, all the measurable properties of the lava are still up
for grabs," Peters said. Even the lava's temperature is
only a guess — it's never been directly measured. That's partly
because of the risk of death from flying bombs, and partly because
the lake is ensconced in a 330-foot-deep (100 m) crater. "The pipe
dream is to do what's called volcano fishing, which is instruments
dangled from cables into the lake," Peters said.
