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
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.
PHOTO GALLERY: HIGH-SPEED GEOLOGY IN AFRICA
Click on a picture to launch the image gallery (9 Photos).
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
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
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.