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Saudi Arabia
Topography and Natural Regions
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 .
Data as of December 1992
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