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WEEKLY NEWSLETTER
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Saudi Arabia
Index
Figure 4. Topography
The Arabian Peninsula is an ancient massif composed of stable
crystalline rock whose geologic structure developed concurrently
with the Alps. Geologic movements caused the entire mass to tilt
eastward and the western and southern edges to tilt upward. In
the valley created by the fault, called the Great Rift, the Red
Sea was formed. The Great Rift runs from the Mediterranean along
both sides of the Red Sea south through Ethiopia and the lake
country of East Africa, gradually disappearing in the area of
Mozambique, Zambia, and Zimbabwe. Scientists analyzing
photographs taken by United States astronauts on the joint United
States-Soviet space mission in July 1975 detected a vast
fan-shaped complex of cracks and fault lines extending north and
east from the Golan Heights. These fault lines are believed to be
the northern and final portion of the Great Rift and are presumed
to be the result of the slow rotation of the Arabian Peninsula
counterclockwise in a way that will, in approximately 10 million
years, close off the Persian Gulf and make it a lake.
On the peninsula, the eastern line of the Great Rift fault is
visible in the steep and, in places, high escarpment that
parallels the Red Sea between the Gulf of Aqaba and the Gulf of
Aden. The eastern slope of this escarpment is relatively gentle,
dropping to the exposed shield of the ancient landmass that
existed before the faulting occurred. A second lower escarpment,
the Jabal Tuwayq, runs north to south through the area of Riyadh.
The northern half of the region of the Red Sea escarpment is
known as the Hijaz and the more rugged southern half as Asir. In
the south, a coastal plain, the Tihamah, rises gradually from the
sea to the mountains. Asir extends southward to the borders of
mountainous Yemen. The central plateau, Najd, extends east to the
Jabal Tuwayq and slightly beyond. A long, narrow strip of desert
known as Ad Dahna separates Najd from eastern Arabia, which
slopes eastward to the sandy coast along the Persian Gulf. North
of Najd a larger desert, An Nafud, isolates the heart of the
peninsula from the steppes of northern Arabia. South of Najd lies
one of the largest sand deserts in the world, the Rub al Khali
(see
fig. 4).
Data as of December 1992
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