Among the first things that evoke eye-popping by the new visitor to Saudi Arabia's Eastern Province are the jebels.
A jebel (also called jabal) is a fairly flexible word that can mean either hill or mountain. The plural, actually, is jibal, but they're jebels to most Americans.
In the area of Aramco's oil operations, they are sometimes seen in solitude, standing in the desert like lost shepherds. Sometimes they're in pairs or in clusters.
They may be just dreary mounds of rock and gravel; but the many forms they take are weird, or grotesque, or stately, or like something sketched by an artist with a penchant for the abstract.
Naturally, one of the first questions that comes to mind is: what caused these strange formations, these bodies of rock poking up like haystacks from the surrounding plain or desert?
The answer is simple: water erosion with some recent modifications by the wind. The jebels, like a great numbers of other erosional features we see on the earth today, were fashioned by the action of water relentlessly wearing away the rock. In this arid area, the transformation took place when water was abundant, long before recorded history.
Over millions and millions of years the earth's surface has changed again and again as the result of heat, pressure, and mountain-making activities within. As a matter of fact, earthquakes and volcanic action are indications that the earth's surface is still changing.
Powerful subterranean pressures folded the rock layers in many places, pushing up highlands as though a giant fist were shoving up high spots under a blanket. As a result of this activity, the rock has faulted—zones of cracks and fractures—along where it had been forced up. And on these areas, rain and snow water, falling and flowing in the new highlands, chewed away voraciously at the faulted areas, leaving only the more resistant rock masses as surface remnants.
Some jebels close to- the Persian Gulf are relatively "young"—that is to say, only a few thousand years old and show less signs of wind erosion than the older jebels, because wind and sand can't wear away a rock surface as fast as water.
How do geologists determine the age of a jebel?
The best way to estimate the age of rock is by determining the fossil content of the various layers. These tell-tale marine animal and vegetable remains left in the rock accurately date the age in which the sediments were laid down in ancient seas. But what if there are no fossil clues?
Then the age of a jebel can also be estimated by matching the layers of rock in the jebel and under it with the same type of layers in nearby hills and escarpments. Undercut to its present outline by erosion, the jebel was very probably part of some nearby structure long ago.
Jebels hold an enduring place in Aramco's. history. It could almost be said that they were the reason for the birth of the oil industry in Saudi Arabia. Geologists on Bahrain Island off die mainland of Arabia, where oil had already been discovered, could see the silhouettes of jebels on clear days, and they looked very much like the same sort of structures that meant oil across the Gulf of Bahrain.
That's why it happened that more than 27 years ago, in 1933, the first two American geologists, bearded and wearing the familiar Arab dress, waded ashore at a little coastal fishing village named Jubail. And jubail is the diminutive of jebel—a little hill.
