Volcanic
Riddle: Burst in Mount Etna Eruptions Puzzles Experts
Mount
Etna is spitting lava more violently than it has in years, and
scientists are baffled as to why. Despite being the world's
most-studied volcano, the Sicilian mountain is also its most
unpredictable.
26
May, 2013
The
volcano is raging. Fountains of lava, some taller than the Eiffel
Tower, shoot from its mouth every few weeks, flowing in red-hot
streams into the surrounding valleys. There have been 13 eruptions
since the beginning of February.
Mount
Etna, 3,329 meters (10,922 feet) high, towers majestically above the
Sicilian city of Catania. In June, the United Nations Educational,
Scientific and Cultural Organization (UNESCO) will decide whether to
list it as a World Heritage Site. Etna is considered the most heavily
studied volcano in the world, and it is thoroughly wired with
sensors. In addition to lava, Etna spits out vast amounts of data --
several gigabytes a day, coming from magnetic field sensors, GPS
altimeters and seismic sensors.
Despite
this wealth of data, Etna still poses a conundrum to scientists. "The
eruptions in recent weeks have been unusually fierce and explosive,"
reports German volcanologist Boris Behncke, who monitors the mountain
together with a few hundred colleagues at Italy's National Institute
of Geophysics and Volcanology (INGV). "There have been lava
fountain events in the past, but rarely in such rapid succession."
Behncke
has fallen under Etna's spell. During the day, he maps the lava
flows; at night, he hikes along its slopes. His Twitter hash tag is
"@etnaboris." The volcano is the first thing he sees when
he looks out of his bedroom window every morning.
"This
time, the range of ash fall is much wider than usual," says
Behncke. A layer of black ash covers cars as far as 50 kilometers (31
miles) away.
Even
in ancient times, people marveled at the forces that were capable of
shooting fountains of lava into the sky. In Greek and Roman
mythology, the volcano is represented by a limping blacksmith
swinging his hammer as sparks fly. Legend has it that the natural
philosopher Empedocles jumped into the crater 2,500 years ago. What
he found there remained his secret, because he never returned. All
that remained of him were his iron shoes, which the mountain later
spat out.
A
Champagne Bottle under Pressure
For
many geologists today, Etna is still the most inscrutable volcano in
the world. The mountain is located at precisely the spot where the
African and European tectonic plates rub against each other like two
giant ice floes. At this plate margin, lava with low viscosity flows
upward from a depth of 30 kilometers into a reservoir of magma two
kilometers beneath the summit.
"The
stream of magma doesn't move uniformly, but in spurts, vibrating as
if it were in a hydraulic pump," explains Stuttgart geophysicist
Rolf Schick. "This makes Etna so unpredictable." Schick has
been a star among volcanologists since 1972, when he caused a stir
with his new discoveries about Etna. Using seismic sensors, he
discovered a "pulse rate" of sorts in the stream of magma,
which is forced through the vent at a rate of 72 beats per minute --
coincidentally, at a rate similar to that of the human heartbeat.
Schick
spent 40 years traveling repeatedly to Sicily to explore Etna. "I
used to believe that we would soon be able to predict volcanic
eruptions," says the scientist, who turns 80 next month. "Today,
I'm no longer certain that we'll ever succeed."
On
one trip, Schick was traveling near the town of Nicolósi, which has
been repeatedly destroyed by streams of lava. Based on the volcanic
pulse he had measured, the geophysicist recognized that a molten
heart was beating underneath him. The magma was only 400 meters
beneath the surface, and an outbreak seemed imminent.
But
nothing happened.
Etna
is currently behaving like a champagne bottle under pressure. The
magma, a foam-like brew of gas and red-hot molten rock, has been
flowing to the surface more quickly in recent years.
At
the moment, the mountain is belching out about a million tons of
water vapor and more than 50,000 tons of carbon dioxide each day. As
they ascend, the gas bubbles expand with lighting speed, and if they
cannot readily escape, they hurl clumps of magma into the air like
oversized champagne corks.
"There
have been violent eruptions like this once every few thousand years,
as, for example, in the year 122 B.C.," says Behncke. The
scientist also expects a destructive outbreak on the eastern flank in
a few months or years. "This is relatively normal for Etna, but
society has changed tremendously. It's become much more difficult
today to carry out an evacuation."
Translated
from the German by Christopher Sultan
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