Arabian Peninsula

Arabia, the largest peninsula of Asia, in the southeastern part of the continent. It is washed on the west by the Red Sea, on the south by the Gulf of Aden and the Arabian Sea, and on the east by the Gulf of Oman and the Persian Gulf. The northern boundary of the Arabian Peninsula is usually drawn approximately along the 30°N parallel. It occupies an area of about 3 million sq km. The shorelines are straight and slightly rugged. Included as part of the Arabian Peninsula are the southern part of Iraq, Kuwait, Saudi Arabia, the Arab Republic of Yemen, the People’s Democratic Republic of Yemen, Oman, Qatar, and the United Arab Emirates.

Geological structure and relief. The Arabian Peninsula constitutes the northeastern part of the ancient African-Arabian platform. Crystalline and metamorphic Proterozoic rocks of the Nubian-Arabian shield form outcroppings on the west and in the center of the Arabian Peninsula, while rocks of the Arabian-Aden-Somali shield form outcroppings on the extreme southwest. Axial parts of the shield are dissected by young grabens of the Red Sea and Gulf of Aden. The southern and western portions of the Arabian Peninsula have experienced recurrent activization (particularly starting at the end of the Cretaceous era). Outflows of basalts occurred along young fracture lines, while volcanic buttes occurred in the southwest along fault scarps running out to the Red Sea. Prolonged denudation of the shields formed by crystalline and metamorphic rocks brought about a topography of terraced highlands and plateaus elevated to 1,800–2,300 m.

The eastern portion of the Arabian Peninsula is a platform of a bench in which base rock strata are submerged under a sedimentary mantle consisting predominantly of Jurassic, Cretaceous, and Cenozoic limestones and sandstones. The lowest areas of the Arabian Peninsula are found in this region: the Hasa depression with elevation points below 200 m. Large petroleum deposits have been discovered on the shoreline of the Persian Gulf.

In the center of the peninsula, rocks of the platform mantle frame the Nubian-Arabian shield in the form of cuesta escarpments extending over a stretch longer than 1,200 km. Masses of incoherent sands are extensively developed: the Rub’ al Khali and the Dahana deserts; in the north the Great Nafud, with its sands and hammadas. The southern border of the Arabian Peninsula is formed by the highly elevated (to 2,469 m) bedded Hadhramaut plateau pierced by numerous wadi valleys. In the southwest a lava-bed plateau comprises an anticlinal mass overlain by thick sedimentary and igneous strata with several volcanoes and peaks reaching to 3,600 m (Mount Nabi Shaib). Along the west littoral of the Red Sea extends a narrow strip of desert with saline soils, sands, and rock debris (the southern part of this region is known as Tihamah). The extreme southeast features a region marked by folded medium highlands of Alpine age in blocks, with extensive development of basic and ultrabasic magmatic rocks (the Akhdar ridges reaching to 3,019 m, Hajar al Sharqii, and others).

Climate. The climate of the southern and central parts of the Arabian Peninsula is tropical and modified by the trade winds. January temperatures range from 14°C (Riyadh) to 24.8°C (Aden); July temperatures soar to 33.4°C (Riyadh), with peak temperatures running as high as 55°C. The tropical regions of the Arabian Peninsula receive scanty rainfall. Precipitation is about 100 mm a year, with less than 50 mm a year in the south (most of the precipitation occurs in the summer months). Annual precipitation increases to 700–900 mm on the western slopes of the mountains in the southwestern part of the peninsula when these regions are visited by the monsoons, and up to 500 mm precipitation occurs in the mountainous areas of the southeastern part. In the extreme north the climate is subtropical with winter cyclonic precipitation; the summer is dry. Precipitation is 150–300 mm each year. The January temperature is 10–15°C; the temperatures drop to below zero when cold air sweeps in from the north.

Rivers and lakes. The low water runoff to the surrounding bodies of water and the sparse network of rivers and lakes are typical. Constant water streams are found in the south and in the southwest (Masila, Tiban, and other rivers). Wadis thread the peninsula in conformity with the general slope of the surface from west to east; most of the wadis terminate blindly in desert sands; the largest wadis are al-Rummah, extending over 1,000 km in length, and al-Dawasir. Underground waters and karst springs in the central part of the cuesta region of the Nejd are significant. Abundant springs come to the surface on the shoreline of the Persian Gulf (Hasa) and are connected with stratal waters flowing out from lower strata. The dearth of fresh water has necessitated construction of large desalini-zation plants in the oil-rich districts (Kuwait).

Soils and flora. About 95 percent of the surface of the Arabian Peninsula is occupied by tropical desert with primitive soils or dispersed and semifastened sand; the salinized depressions contain solonchak soils and salt flats with succulent saltworts, seepweeds, and other plants. Small areas of cereal-growing steppes appear intermittently in the center; in the red-brown soils of the south there are desiccated savannas dominated by acacias. There are subtropical semideserts and deserts in the north; arid steppes dominated by sagebrush, angustifoliate cereals, and subshrub-bery are found on sierozems and gray-brown and brown soils. Sparse thickets of acacias, Jerusalem thorns, and tamarisks flourish along the wadi beds and in oases of piedmont zones. The richest communities are the tropical monsoon-watered areas of the mountainous southwest and southeast, which feature tamarinds, candelabra-like milkweeds (spurges), acacia, and other plants; pistachio and olive trees and various evergreen shrubs prosper at heights from 1,500 to 1,800 m; mesophytic meadows are found higher up. The soils are either mountain red-brown soils or dark-hued on volcanic rock. Cultivated plants include the date palm, coffee, fruit trees, wheat, barley, corn, and millet.

Fauna. The southern and central parts of the Arabian Peninsula belong to the Saharan subregion of the Ethiopic region, while the north belongs to the Mediterranean sub-region of the Palearctic region. Ungulate fauna—including species of antelope, gazelle, and onager—are typical; shrews and jerboas also flourish. Predators are represented by foxes, hyenas, and jackals. There are many reptiles and birds, including migratory birds. Locust breeding centers are located on the Arabian Peninsula.

Natural regions. (1) Western Arabia is a desert, medium-altitude, terraced highland dissected by deeply entrenched wadi channels that descend in broken escarpments to the Red Sea. (2) The volcanic plateau of the southwestern portion of the Arabian Peninsula has greater precipitation, tropical forests in the south with sparse wooded areas, and savannas on the east. (3) The high stratified plateaus of the southern border regions of Hadhramaut have an impressively large number of oases. (4) The region of cuesta stratified plains is interlaced with wadi valleys with some areas covered by sand; there is winter and spring shrub and grass vegetation; oases are located at outcroppings of karst springs. (5) The sand deserts of Rub al Khali, Dahana, and the Great Nafud are medium and low (on the east) stratified plains with infrequent oases. (6) The region of hills and low mountains in the southeast has savannas and arid sparsely wooded areas.

REFERENCES

Zarubezhnaia Aziia, Fizicheskaia geografiia, Moscow, 1956.
Birot, P., and J. Dresch. Sredizemnomor’e, vol. 2. Moscow, 1962. (Translated from French.)
Gourou, P. Aziia. Moscow, 1956. (Translated from French.)
Stamp, L. D. Asia, 9th ed. London-New York, 1957.
Cressey.G., et al. Land and Life in Southwest Asia. Chicago, 1960.

N. V. ALEKSANDROVSKAIA

Arabian Peninsula