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 Arabic
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.
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.
