Science News - July 2, 2011

On the move In 2005, the Envisat satellite captured how tectonic plates pulling apart in the Afar region caused the greatest ground deformation ever seen from space. At left, the rainbow pattern reveals which parts of the ground surrounding the Dabbahu rift segment moved between May and October of that year— due almost entirely to a September rifting event. Other analyses of ground motion ( middle and right) reveal that movement was concentrated along a thin band in the rift zone.

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Line of sight (cm)

Line of sight (m)

Semera, and a nearby dam lie atop the
many fault lines that crisscross the
region. Both were planned long before
the September 2005 eruption and are
unlikely to be decommissioned in a place
where starvation and disease are more
pressing concerns than geologic hazards.

Still, Ayele says he and his colleagues spend a lot of time working to educate the local government and people about the earthquake risk.

“We had 48 hours of lava heaven,” says
Field. “I watched my rocks being born.”
Erta Ale’s lava is thinner and less
sticky than that at Dabbahu, suggest-
ing that it is erupting directly from the
mantle rather than sitting in reservoir
chambers for a while, says Field. (Magma
undergoes chemical changes when it sits
in a reservoir, such as by melting the sur-
rounding rocks and incorporating their
minerals.) Erta Ale is also much closer
to the Red Sea’s spread-
ing center, so the ground
there may more closely
resemble ocean crust than
the Dabbahu rift zone
does at the moment. How
the two areas of volcanic
activity are related — and
how they fit into the big-
ger tectonic triple junction
picture — remains to be
explored.

“We’re not done yet,” says Ebinger.
Already, researchers have recorded a
flurry of earthquakes to the east, about
100 kilometers offshore in the Gulf of
Aden. That activity, in December 2010,
could mean a dike was injected there
below the seafloor, which may be related
to the activity at Dabbahu. “It’s likely
when stress is relieved at one point it can
“It’s likely
when stress is
relieved at one
point it can
trigger another
point that is
critically close
to failure.”
ATALAY AYELE

In some ways, Afar’s chronic volcanism has become an everyday part of life in the region. The Afar people have adapted to gather water for themselves and their goats from natural fumaroles, or steam vents. First, says Field, the locals hold a piece of obsidian glass up to a vent; if it turns cloudy, that signifies too many poisons are in the steam. But if the obsidian stays clear, the people lay reeds down into the vent, then use a can to collect the water that condenses on and drips off the reeds.

In the long term, Afar may need to brace for volcanoes and earthquakes for quite a while. Scientists aren’t sure exactly how long Afar will remain highly active, but they do have one point of comparison: the Krafla eruptions in northern Iceland, which took place over nearly a decade in the 1970s and 1980s. Eruptions at Krafla poured out lava for several years, then quieted down, then burst out again with a lot of magma right at the end.

At Afar, “things have been suspiciously quiet since May 2010,” Wright says, with no dikes or eruptions along the Dabbahu segment. But if Krafla offers a comparison, Afar might yet expect a lot of magma to pour out in another couple of years. Afar also has more magma underlying it to start with than Krafla did.

In other ways, modern life has not
adapted so well to local geology. The
newly built regional capital of Afar,
trigger another point that is critically
close to failure,” Ayele says. But scien-
tists can’t take a ship to study the region,
because of the threat of Somali pirates.