From: Biniam Tekle (biniamt@dehai.org)
Date: Tue Nov 03 2009 - 11:50:42 EST
http://www.sciencedaily.com/releases/2009/11/091102172037.htm
African Desert Rift Confirmed As New Ocean In The Making
ScienceDaily (Nov. 3, 2009) — In 2005, a gigantic, 35-mile-long rift broke
open the desert ground in Ethiopia. At the time, some geologists believed
the rift was the beginning of a new ocean as two parts of the African
continent pulled apart, but the claim was controversial.
Now, scientists from several countries have confirmed that the volcanic
processes at work beneath the Ethiopian rift are nearly identical to those
at the bottom of the world's oceans, and the rift is indeed likely the
beginning of a new sea.
The new study, published in the latest issue of *Geophysical Research
Letters*, suggests that the highly active volcanic boundaries along the
edges of tectonic ocean plates may suddenly break apart in large sections,
instead of little by little as has been predominantly believed. In addition,
such sudden large-scale events on land pose a much more serious hazard to
populations living near the rift than would several smaller events, says
Cindy Ebinger, professor of earth and environmental sciences at the
University of Rochester and co-author of the study.
"This work is a breakthrough in our understanding of continental rifting
leading to the creation of new ocean basins," says Ken Macdonald, professor
emeritus in the Department of Earth Science at the University of California,
Santa Barbara, and who is not affiliated with the research. "For the first
time they demonstrate that activity on one rift segment can trigger a major
episode of magma injection and associated deformation on a neighboring
segment. Careful study of the 2005 mega-dike intrusion and its aftermath
will continue to provide extraordinary opportunities for learning about
continental rifts and mid-ocean ridges."
"The whole point of this study is to learn whether what is happening in
Ethiopia is like what is happening at the bottom of the ocean where it's
almost impossible for us to go," says Ebinger. "We knew that if we could
establish that, then Ethiopia would essentially be a unique and superb
ocean-ridge laboratory for us. Because of the unprecedented cross-border
collaboration behind this research, we now know that the answer is yes, it
is analogous."
Atalay Ayele, professor at the Addis Ababa University in Ethiopia, led the
investigation, painstakingly gathering seismic data surrounding the 2005
event that led to the giant rift opening more than 20 feet in width in just
days. Along with the seismic information from Ethiopia, Ayele combined data
from neighboring Eritrea with the help of Ghebrebrhan Ogubazghi, professor
at the Eritrea Institute of Technology, and from Yemen with the help of
Jamal Sholan of the National Yemen Seismological Observatory Center. The map
he drew of when and where earthquakes happened in the region fit
tremendously well with the more detailed analyses Ebinger has conducted in
more recent years.
Ayele's reconstruction of events showed that the rift did not open in a
series of small earthquakes over an extended period of time, but tore open
along its entire 35-mile length in just days. A volcano called Dabbahu at
the northern end of the rift erupted first, then magma pushed up through the
middle of the rift area and began "unzipping" the rift in both directions,
says Ebinger.
Since the 2005 event, Ebinger and her colleagues have installed seismometers
and measured 12 similar -- though dramatically less intense -- events.
"We know that seafloor ridges are created by a similar intrusion of magma
into a rift, but we never knew that a huge length of the ridge could break
open at once like this," says Ebinger. She explains that since the areas
where the seafloor is spreading are almost always situated under miles of
ocean, it's nearly impossible to monitor more than a small section of the
ridge at once so there's no way for geologists to know how much of the ridge
may break open and spread at any one time. "Seafloor ridges are made up of
sections, each of which can be hundreds of miles long. Because of this
study, we now know that each one of those segments can tear open in a just a
few days."
Ebinger and her colleagues are continuing to monitor the area in Ethiopia to
learn more about how the magma system beneath the rift evolves as the rift
continues to grow.
Additional authors of the study include Derek Keir, Tim Wright, and Graham
Stuart, professors of earth and environment at the University of Leeds,
U.K.; Roger Buck, professor at the Earth Institute at Columbia University,
N.Y.; and Eric Jacques, professor at the Institute de Physique du Globe de
Paris, France.
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