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Watching a continent splinter.


Ancient human ancestors inhabited some of the rawest land on Earth, amid the East African Rift Valley rift valley, elongated depression, trough, or graben in the earth's crust, bounded on both sides by normal faults and occurring on the continents or under the oceans. The central flat block forming the trough slips downward relative to the crustal blocks on either side. The appearance is that of a fallen keystone in a broken arch. Rift valleys form by tensional forces, typically those associated with the initiation of plate separation (see plate tectonics tectonic /tec·ton·ic/ (tek-ton´ik) pertaining to construction.).. There, two sections of the planet's skin are pulling apart like a fresh wound. For years, geoscientists have wondered why this gash gash (gsh)
v.
To make a long, deep cut in; slash deeply.
n.
1. A long, deep cut.
2. A deep flesh wound.
 disappears south of Mozambique

Mozambique, country, Africa

Mozambique (mō'zəmbēk`), officially Republic of Mozambique, republic (2005 est. pop. 19,407,000), 302,659 sq mi (784,090 sq km), SE Africa.
. Two researchers now have an answer.

The East African rift marks the boundary between two tectonic plates: the Nubian plate to the west and the Somalian plate to the east. A general rule of plate tectonics plate tectonics, theory that unifies many of the features and characteristics of continental drift and seafloor spreading into a coherent model and has revolutionized geologists' understanding of continents, ocean basins, mountains, and earth history.

Development of Plate Tectonics Theory

 is that such rifts must hook up to other plate boundaries, but researchers have had trouble tracing the connection of the East African rift. South of Mozambique, there are no earthquakes or other signs of disturbance like those seen along the rift to the north.

Dezhi Chu of Exxon Production Research Co. and Richard G. Gordon of Rice University, both in Houston, tracked the continuation of the East African rift by studying ocean rocks. Between Africa and Antarctica Antarctica (ăntärk`tĭkə, –är`tĭkə), the fifth largest continent, c.5,500,000 sq mi (14,245,000 sq km), asymmetrically centered on the South Pole and almost entirely within the Antarctic Circle.

Geology and Geography



Antarctica consists of two major regions: W Antarctica (c.
, there is a rift in the seafloor where the crust spreads apart and new rock is born. In the process, the two African plates inch away from Antarctica.

Using Antarctica as a signpost, Chu and Gordon discerned the motion between the Nubian and Somalian plates. Instead of pulling straight apart, the two plates rotate like scissors blades around a pivot point
Pivot Point
A technical indicator derived by calculating the numerical average of a particular stock's high, low and closing prices.

Notes:
The pivot point is used as a predictive indicator. If the following day's market price falls below the pivot point, it may be used as a new resistance level. Conversely, if the market price rises above the pivot point, it may act as the new support level.
 east of South Africa, the two report in the March 4 Nature. In the region of the East African rift, far north of the pivot point, the two plates are separating by 6 millimeters a year. Just south of the pivot point, the two plates are crushing together at a rate of only 2 mm per year, so slowly that they don't often produce large earthquakes.

By understanding the motion, or kinematics kin·e·mat·ics (kn-mt, of these two plates, geoscientists will have more success in resolving how all Earth's plates behave. "It solves, in a sense, this 30-year mystery of how the East African rift fits in kinematically in the plate-tectonic scheme," says Gordon.
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Title Annotation:watching continental drift in the Great Rift Valley
Publication:Science News
Article Type:Brief Article
Geographic Code:60AFR
Date:Mar 20, 1999
Words:329
Previous Article:When Meteorologists See Red.(research on climactic change)
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