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March 15, 2006

AFRICA'S NEW OCEAN

A Continent Splits Apart

By Axel Bojanowski

Normally new rivers, seas and mountains are born in slow motion. The
Afar Triangle near the Horn of Africa is another story. A new ocean is
forming there with staggering speed -- at least by geological standards.
Africa will eventually lose its horn.

Geologist Dereje Ayalew and his colleagues from Addis Ababa University
were amazed -- and frightened. They had only just stepped out of their
helicopter onto the desert plains of central Ethiopia when the ground
began to shake under their feet. The pilot shouted for the scientists to
get back to the helicopter. And then it happened: the Earth split open.
Crevices began racing toward the researchers like a zipper opening up.
After a few seconds, the ground stopped moving, and after they had
recovered from their shock, Ayalew and his colleagues realized they had
just witnessed history. For the first time ever, human beings were able
to witness the first stages in the birth of an ocean.

Normally changes to our geological environment take place almost
imperceptibly. A life time is too short to see rivers changing course,
mountains rising skywards or valleys opening up. In north-eastern
Africa's Afar Triangle, though, recent months have seen hundreds of
crevices splitting the desert floor and the ground has slumped by as
much as 100 meters (328 feet). At the same time, scientists have
observed magma rising from deep below as it begins to form what will
eventually become a basalt ocean floor. Geologically speaking, it won't
be long until the Red Sea floods the region. The ocean that will then be
born will split Africa apart.

The Afar Triangle, which cuts across Ethiopia, Eritrea and Djibouti, is
the largest construction site on the planet. Three tectonic plates meet
there with the African and Arabian plates drifting apart along two
separate fault lines by one centimeter a year. A team of scientists
working with Christophe Vigny of the Paris Laboratory of Geology
reported on the phenomenon in a 2006 issue of the Journal of Geophysical
Research. While the two plates move apart, the ground sinks to make room
for the Red Sea and the Gulf of Aden.

Bubbling magma and the smell of sulphur

A third crevice cuts south, splitting not far from Lake Victoria. One
branch of the rift runs to the east, the other to the west of the lake.
The two branches of this third crevice are moving apart by about one
millimeter a year.

The dramatic event that Ayalew and his colleagues witnessed in the Afar
Desert on Sept. 26, 2005 was the first visual proof of this process --
and it was followed by a week-long series of earthquakes. During the
months that followed, hundreds of further crevices opened up in the
ground, spreading across an area of 345 square miles. "The earth has not
stopped moving since," geophysicist Tim Wright of the University of
Oxford says. The ground is still splitting open and sinking, he says;
small earthquakes are constantly shaking the region.

Scientists have made repeated trips to the area since the drama of last
September. Locals have reported a number of new cracks opening in the
ground, says geologist Cynthia Ebinger from the University of London,
and during each visit, new crevices are discovered. Fumes as hot as 400
degrees Celsius (752 degrees Fahrenheit) shoot up from some of them; the
sound of bubbling magma and the smell of sulphur rise from others. The
larger crevices are dozens of meters deep and several hundred meters
long. Traces of recent volcanic eruptions are also visible.

In a number of places, cracks have opened up beneath the thin layer of
volcanic ash that covers the region. As there is no ash in the fissures,
it's clear that they opened up after the volcanic eruptions, most of
which took place at the end of September or in October, 2005. A number
of locals who fled the eruptions have reported that a black cloud of ash
-- spewed out of the Dabbahu volcano -- darkened the sky for three days.

A new ocean floor on the Earth's surface

Basalt magma has risen into some of the crevices. For the moment, Ayalew
explains, the lava seems not to be rising further. A number of recent
eruptions, though, have left layers of new basalt lava on the Earth's
surface. And it's the exact same kind of lava that spews out of volcanic
ridges deep under the ocean -- a process which slowly pushes older lava
sediments away on either side. The process has only just begun in the
Afar Triangle -- and scientists for the first time can witness the birth
of a new ocean floor.

The source of the African magma looks to be a gigantic stream of molten
rock rising from beneath the Earth's crust and slicing through the
African continental plate like a blow torch. It's a process that began
thirty million years ago when lava broke through the continent for the
first time, separating the Arabian Peninsula from Africa and creating
the Red Sea.

Now, it's the Afar Triangle's turn and it's sinking rapidly. Large areas
are already more than 100 meters (328 feet) below sea level. For now,
the highlands surrounding the Denakil Depression prevent the Red Sea
from flooding these areas, but erosion and tectonic plate movement are
continually reducing the height of this natural barrier. The Denakil
Depression, which lies to the east of Afar, is already prey to regular
floods -- each flood leaving behind a crust of salt.

Africa to lose its horn

The chain of volcanoes that runs along the roughly 6,000 kilometer
(3,730 mile) long East African Rift System offers further testimony to
the breaking apart of the continent. In some areas around the outer
edges of the Rift System, the Earth's crust has already cracked open,
making room for the magma below. From the Red Sea to Mozambique in the
south, dozens of volcanoes have formed, the best known being Mt.
Kilimanjaro and Mt. Nyiragongo.

These fiery mountains too will one day sink into the sea. Geophysicists
have calculated that in 10 million years the East African Rift System
will be as large as the Red Sea. When that happens, Africa will lose its
horn.

© SPIEGEL ONLINE 2006