March 16, 2012. Samuel Valero
Lofty, rugged, and austere, the great Iranian range is a superb example of mountains that were formed by folding of the earth’s outer crust. The Zagros is the rugged, lofty mountain barrier that forms Iran’s western frontier. The range rises in northwestern Iran near its border with Turkey and the U.S.S.R.
It extends southeastward for about 1,100 miles (1,770 kilometers) to the Strait of Hormuz, the strategic narrows linking the Persian Gulf and the Gulf of Oman.
Many of the peaks and ridges in the Zagros exceed 10,000 feet (3,050 meters). The highest, the snowcapped volcanic summit of Mount Sabalan near Tabriz, reaches 15,592 feet (4,752 meters). To the east the Zagros encloses Iran’s high central plateau. On the west the mountains drop down to the Mesopotamian plains of Iraq and the Persian Gulf.
The range was born of a collision of two of the crustal plates that drift restlessly about on the surface of the earth’s molten interior. Moving slowly but relentlessly northeastward, the so-called Arabian plate collided with the Eurasian mainland. As the leading edge of the Arabian plate was forced down beneath the Eurasian plate, the great mountain range was heaved up along the collision zone.
The results of this impact were far from uniform, however, and the northwestern end of the Zagros contrasts dramatically with its southeastern counterpart. The northwest is a heavily faulted plateau where blocks of rock were thrust up along fractures in the earth’s crust to form mountain ridges, while other blocks sank to form basins. Iran’s largest lake, salty Lake Urmia to the west of Tabriz, lies in one of these landlocked basins. Lava erupted along many of the fault lines, dotting the countryside with massive volcanic cones such as Sahand and Mount Sabalan. The region, moreover, is still unstable. A few of the volcanoes continue to smolder, and the area is periodically wracked by violent earthquakes.
The southeastern part of the Zagros, in contrast, is one of the most beautifully folded mountain ranges in the world. Here the colliding crustal plates caused the area’s thick limestone deposits to buckle up in high folds, known as anticlines, separated by downwarps, or synclines. Extending from northwest to southeast is a broad zone of long parallel lines of enormous hogback ridges and deep intervening valleys. In places where compression was very intense, some of the folds were thrust over the tops of their neighbors, like collapsed dominoes.
Despite the rugged terrain and the meager rainfall, people live in the Zagros as they have for centuries. In the more densely populated northern part of the range, grains, fruits, and vegetables are grown in the fertile valleys. Farther south, nomadic tribes continue to make their traditional seasonal migrations. In summer they travel to the highlands to graze their flocks of sheep and goats on alpine meadows; in winter they return to the sheltered lowland valleys. Anna writes for the Majorca Guide and loves travelling and writing about travel.
Updated March 16, 2012. Published February 13, 2012. Samuel Valero
