Giant crack in Africa formed in just days

22:17 04 November 2009 by MacGregor Campbell

A crack in the Earth's crust – which could be the forerunner to a new ocean – ripped open in just days in 2005, a new study suggests. The opening, located in the Afar region of Ethiopia, presents a unique opportunity for geologists to study how mid-ocean ridges form.

The crack is the surface component of a continental rift forming as the Arabian and African plates drift away from one another. It began to open up in September 2005, when a volcano at the northern end of the rift, called Dabbahu, erupted.

The magma inside the volcano did not reach the surface and erupt as a fountain of lava – instead, it was diverted into the continental rift underground. The magma cooled into a wedge-shaped "dike" that was then uplifted, rupturing the surface and creating a 500-metre-long, 60-metre-deep crack.

Using sensor data collected by universities in the region, researchers led by Atalay Ayele of Addis Ababa University in Ethiopia reconstructed the sequence of seismic events that led to the crack's formation. They found that a 60-kilometre-long, 8-metre-wide dike of solidified magma formed in the rift, causing the crack, in a matter of days.

'Stunning' ferocity

Similar dikes in Iceland are typically around 10 kilometres long and 1 metre wide and can take years to form. The new study shows the formation of dikes can occur in larger segments – and over much shorter periods of time – than previously thought.

"The ferocity of what we saw during this episode stunned everyone," says Cynthia Ebinger, a team member at the University of Rochester in New York.

While the Mount Dabbahu rift is still hundreds of kilometres inland, Ebinger says it could continue to widen and lengthen. "As the plates keep spreading apart, it will end up looking like the Red Sea," she says.

New ocean

Eventually it could reach the east coast of Ethiopia and fill up with seawater. "At some point, if that spreading and rifting continues, then that area will be flooded," says Ken Macdonald, a marine geophysicist at the University of California, Santa Barbara, who was not involved with the study.

Ebinger says this won't happen any time soon – it would take around 4 million years for the crack to reach the size of the Red Sea. Other areas in the Afar region are below sea level, however, and could see flooding before that if similar rifting occurs near the coastal volcanoes to the north and east that form a natural levee against the sea.

Macdonald says the process of continental plates spreading apart and filling in with magma is analogous to what happens on the deep seafloor at mid-ocean ridges, which are difficult to study because they lie a few kilometres under water. "This is very exciting in terms of its implications for the deep ocean and how mid-ocean ridges work," he told New Scientist.

Journal reference: Geophysical Research Letters (doi:10.1029/2009GL039605)