Ocean birth through rifting and rupture

Article By:

Calais, Eric Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana.

Ebinger, Cynthia Department of Geology, Royal Holloway University of London, London, United Kingdom.

Yirgu, Gezahegn Geology and Geophysics Department, Addis Ababa University, Addis Ababa, Ethiopia.

Wright, Tim Department of Earth Sciences, Oxford University, Oxford, United Kingdom.

Lewi, Elias Geophysical Observatory, Addis Ababa University, Addis Ababa, Ethiopia.

Last reviewed:2007

DOI:https://doi.org/10.1036/1097-8542.YB070250

The formation of a new ocean basin begins with the rupture of a more than 100-km-thick (60-mi) continental plate, but only after millions of years of heating and stretching. The deep, fault-bounded valleys above the zones of stretching and heating are called continental rift zones. Fortunately for Earth's inhabitants, the rate of geological processes is extremely slow, and the rupture occurs in episodes separated by hundreds of years. Volcanic and earthquake activity in these episodes affects only a sector of the long narrow rift zones, producing a regular along-axis rift segmentation that is maintained in subsequent episodes. In September-October 2005, a 60-km-long (40-mi) segment of the East African rift system in Ethiopia experienced an intense period of localized deformation. Over 162 moderate [body wave magnitude (mb) > 4.5 to 3.9] earthquakes and an explosive volcanic eruption occurred over a 3-week period. Subsequent field, remote sensing, and modeling studies showed that molten rock (magma) was intruded into the plate beneath this 60-km-long rift segment, with cracks and faults forming in the brittle rocks above the narrow zones of magma injection. Thus, we directly observed a rare event—the injection of an approximately 8-m-wide (26-ft) column of magma that will quickly freeze to form a new strip of ocean floor. Continued monitoring of the activity will provide vital information for seismic and volcanic hazard mitigation in East Africa.

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