Hidden Riches of the Arabian Desert
That long, rich geologic history helps explain the vital importance to the world of this seemingly barren and inhospitable desert. In its northern reaches, the 1,300-mile-long (2,080 km) Arabian Peninsula merges with Arab Asia through the treeless plains of Syria. The highest point lies in Yemen, 12,336-foot (3,760 m) Mount Al-Nabi Shu'ayb. Much of the peninsula is low, dry, and hot, but the southern tip is dominated by the Yemen plateau, with an average elevation of 7,000 feet (2,100 m).
West of the Red Sea the area is bounded by a remarkable line of 2,000-foot-tall (670 m) cliffs that run for some 600 miles (960 km). Caused by a massive uplift of the Earth due to the rifting along the bottom of the Red Sea, the elevation changes from some 600 feet (670 m) at the base of this uplifted line of cliffs to some 3,300 feet (1,100 m) along their lip. These rugged cliffs cut off the desert interior from moist ocean air and have long isolated the distinctive desert people who have made a hard living here for thousands of years. Great sandy, rocky plains with only modest hills mark the rest of the Arabian Desert. Nearly featureless expanses of sand cover perhaps one-third of the total area.
This whole landscape is laid down on top of one of Earth's most remarkable geological features, the African Shield, a mass of Precambrian gneiss that includes rocks formed some 2.6 billion years ago as a great, molten mass deep beneath the surface. Shifts in the Earth have forced this molten mass of rock to the surface in the past 500 to 900 million years, determining the foundation geology of much of Africa.
The final major stage in creating the current landscape began some 35 million years ago when the Red Sea began to open up along this deep crack in the Earth. This created a titanic series of volcanic outbursts some 20 to 30 million years ago. Magma broke through fractures in the rifting crust and burst out onto the surface. In some places, the flood of molten basalts piled on in layers up to 9,800 feet (3,000 m) thick. These almost unimaginable lava floods now form the mountains along the Red Sea margin in Yemen. A second, much smaller volcanic period ended about 10,000 years ago, leaving lava domes and an extensive fault system along the western edge of the desert. Some 18 relatively young volcanic fields are scattered throughout the area, some of them covering 10,000 square miles (25,899 sq km).
The same forces that created these volcanic outbreaks have left several large, uplifted plateaus. That includes most of Jordan east of the Dead Sea, the sandstone mass of Mount Al-Tubayq in the southeast, and several other plateaus that advance to the edge of the Al-Nafud, the great sand desert of the north.