Confirming a Suspected Rift Valley
Geologists Show that Seafloor Dynamics Are at Work in Splitting African Continent.
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.
Potential Hazards of Large-Scale Rifting
The new study, published in 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.
"Rifting In Concert"
"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."
Is Ethiopia Analogous to Ocean-Ridge Rifting?
"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."
Twenty Feet of Rifting in a Few Days
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.
About the University of Rochester
The University of Rochester (www.rochester.edu) is one of the nation's leading private universities.
Located in Rochester, N.Y., the University gives students exceptional opportunities for interdisciplinary
study and close collaboration with faculty through its unique cluster-based curriculum. Its College,
School of Arts and Sciences, and Hajim School of Engineering and Applied Sciences are complemented by
the Eastman School of Music, Simon School of Business, Warner School of Education, Laboratory for Laser
Energetics, Schools of Medicine and Nursing, and the Memorial Art Gallery.
|Aerial view of the rift near Afar, Ethiopia. Image by University of Rochester. Enlarge image.
|Aerial view looking down the rift valley bounded by tall, near-vertical fault scarps. Image by University of Rochester. Enlarge image.
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