The Arabian Peninsula is the largest peninsula in the world, covering about 3,237,500 km² of West Asia between the Red Sea, the Gulf of Aden, the Arabian Sea and the Persian Gulf. Seven countries lie on it: Saudi Arabia, which takes up about two-thirds, Yemen, Oman, the United Arab Emirates, Kuwait, Qatar and the island state of Bahrain, while the southern parts of Iraq and Jordan are often counted too. The peninsula sits on its own tectonic plate, tilted so that a high mountain wall runs down the Red Sea coast and the land slopes east to the Gulf. Its highest point is Jabal an-Nabi Shu'ayb in Yemen at 3,666 m, its largest feature is the Rub' al Khali sand desert, and it has almost no permanent rivers, so its people depend on ancient groundwater and on desalinated seawater.
Seven Countries Sharing 3.2 Million Square Kilometres
The northern edge of the peninsula fades into the Syrian Desert without a clear natural boundary, so it is usually drawn along the northern borders of Saudi Arabia and Kuwait. Inside that line the land is divided very unevenly. Saudi Arabia covers about 2,149,690 km² and is the twelfth-largest country in the world. Yemen follows with about 455,500 km², including its islands, and Oman with about 315,300 km². The four Gulf states are far smaller: the United Arab Emirates at about 83,600 km², Kuwait at about 17,820 km², the Qatar peninsula at 11,571 km² and Bahrain, an archipelago in the Gulf, at about 780 km². Bahrain is the one number that keeps changing, because land reclamation has pushed it up from 665 km² to about 780 km².
The scale is easier to grasp by comparison: the peninsula as a whole is roughly the size of India, a match explored in our article on whether the Arabian Peninsula is bigger than India. Most of it is desert, and the countries' populations crowd into a few places where water and trade come together: the Red Sea ports and holy cities of the Hejaz, the oasis capital Riyadh in the Najd plateau, the Gulf coast from Kuwait City to Dubai, the Batinah coast of Oman and the highland basins of Yemen around Sana'a. Medieval Muslim geographers divided Arabia into four regions along similar lines: the central plateau of Najd and al-Yamama, South Arabia (Yemen, Hadhramaut and southwestern Oman), al-Bahrain on the eastern coast, and the Hejaz with the Tihamah.
The Arabian Plate: Breaking Away from Africa
The shape of the peninsula comes from plate tectonics. For most of geological history Arabia was part of the African plate. Rifting along the line of today's Red Sea began in the Eocene, and Arabia separated from Africa around 25 million years ago, since when the Arabian plate has been moving north toward Eurasia. Its boundaries are all active. To the west the Red Sea Rift is a spreading centre where new ocean floor forms, and the Dead Sea Transform carries the plate edge north through the Levant. To the northeast the plate is colliding with Eurasia along the Zagros fold and thrust belt, pushing up the Zagros Mountains of Iran, and to the east its oceanic crust dives beneath Eurasia at the Makran subduction zone. Today the plate moves north relative to Eurasia at about 2 to 3 cm a year.
The rifting tilted the whole block. The western edge, next to the Red Sea, was lifted into a high escarpment, while the land slopes gently east toward the shallow Persian Gulf, so that the peninsula's great sand seas and its lowest coasts lie on the Gulf side. The opening of the rift also brought volcanism to western Arabia. Fields of basalt called harrats cover large areas of the Hejaz; the biggest, Harrat Rahat, last erupted in 1256 CE, when a lava flow travelled 23 km to stop within 4 km of the holy city of Medina.
Hejaz, Asir and the Red Sea Escarpment
That uplifted western edge forms the Sarawat, the mountain wall running parallel to the Red Sea from the Gulf of Aqaba to Yemen. In Saudi Arabia it has two main parts. The Hejaz Mountains in the north rise to about 2,100 m and fall to around 600 m near a gap in the middle of the coast; their western face drops abruptly to the narrow Red Sea coastal plain, the Tihamah. South of the gap, the Asir Mountains cover about 100,000 km² of the southwest and catch more rain than anywhere else in the kingdom, between 600 mm and over 1,000 mm a year in the wettest places, enough for terraced farming.
Saudi Arabia's highest summit lies here, although which one it is depends on the survey. The authorities officially recognise Jabal Sawda at 3,015 m, near the village of as-Sawda; a 2018 survey measured it at 2,999 m, slightly lower than nearby Jabal Ferwa at 3,002 m. Either way, the crops of the Asir, among them wheat, coffee, vegetables and palms, are mostly grown on steeply terraced mountainsides, and the region also supports cattle, sheep, goats and camels.
Jabal an-Nabi Shu'ayb and the Highlands of Yemen
The Sarawat reach their greatest height in Yemen, where all of the range's summits above 3,000 m stand. The highest is Jabal an-Nabi Shu'ayb, also called Jabal Hadhur, at 3,666 m in Bani Matar District of Sana'a Governorate, west of the capital. It is the highest mountain in Yemen and in Arabia and the 62nd most prominent peak in the world. The Yemeni highlands divide into western and central ranges; the western slopes receive more rain than anywhere else on the peninsula, and in the Haraz Mountains, where fortified villages cling to rocky peaks, summits of 2,800 to 3,300 m rise from feet only 500 m above sea level.
Rain is the reason Yemen has historically been the most densely farmed corner of Arabia. Roman geographers called this region Arabia Felix, "fertile" or "happy" Arabia, a translation of a Greek name attributed to Eratosthenes, to set it apart from the desert interior. Further east along the Gulf of Aden coast, the long valley system of the Hadhramaut carries farming deep into the plateau, and in Oman's Dhofar region the southwest monsoon, known locally as the khareef, brings cloud, drizzle and green hills from mid-June to mid-September, a monsoon summer it shares with Yemen's neighbouring Al Mahrah region.
The Hajar Mountains of Oman and the UAE
On the opposite corner of the peninsula stands a range with a completely different origin. The Hajar Mountains run for about 700 km from the Musandam Peninsula, which juts into the Strait of Hormuz, through the eastern UAE and down the coast of northern Oman, about 50 to 100 km inland from the Gulf of Oman and about 100 km wide. Their highest peak is Jebel Shams at 3,009 m, in the central part of the range.
The Hajar were built by plate collision rather than rifting. In the late Cretaceous the edge of the Arabian continent was pushed beneath oceanic crust, and a great slab of that ocean floor, the Semail Ophiolite, formed about 95 million years ago, was thrust up onto the land. It is one of the world's largest and best-exposed segments of oceanic crust, with volcanic rocks and ultramafic rocks from the upper mantle laid bare on the mountainsides. The range separates the low coastal plain of Oman from the high desert plateau inland.
Rub' al Khali: 650,000 km² of Sand
West of the Hajar begins the Rub' al Khali, the "Empty Quarter", which covers about 650,000 km² of the southern third of the peninsula across parts of Saudi Arabia, Oman, the UAE and Yemen. The 647,500 km² of it inside Saudi Arabia is often described as the world's largest contiguous sand desert. It stretches about 1,000 km long and 500 km wide, and its surface falls from about 800 m in the southwest to near sea level in the northeast. Most of it is erg, with dunes up to 250 m high separated by gravel and gypsum plains, and its sand is reddish-orange from feldspar. On its eastern edge lie the salt flats of Umm al Samim.
The desert was not always this dry. Hardened beds of calcium carbonate, gypsum and marl along its middle mark shallow lakes that existed between about 6,000 and 5,000 years ago, and again between 3,000 and 2,000 years ago. The first documented journeys by non-resident explorers came only in the early 1930s, by the British explorers Bertram Thomas and St John Philby, and Wilfred Thesiger mapped much of it on journeys between 1946 and 1950. The Empty Quarter is the core of the wider Arabian Desert; our Rub' al Khali guide follows its dunes and lake beds in more depth.
Wadis, Fossil Aquifers and Desalination Plants
What Arabia lacks above all is rivers. Saudi Arabia is the largest country in the world without a permanent river. Water flows only after storms, briefly, down dry valleys called wadis, and the low Gulf states have hardly any relief at all: Kuwait's highest point, on the Mutla Ridge, is 306 m, and Qatar's is just 103 m.
Two sources fill the gap. The first is groundwater, much of it non-renewable fossil water stored in deep aquifers during wetter periods long ago. Agriculture has drawn on it heavily and accounts for about 83% of Saudi water use, against 13% for towns and cities. A 2015 study of NASA GRACE satellite data from 2003 to 2013 named the Arabian Aquifer System the most over-stressed aquifer system in the world, with more than 60 million people depending on it. The second source is the sea. In Saudi Arabia about half of drinking water now comes from desalination, around 40% from mined groundwater and only about 10% from surface water in the southwestern mountains. The largest single plant, Ras Al-Khair on the Gulf coast, is operated by the state Saline Water Conversion Corporation; it opened in 2014 as the largest desalination plant in the world, built at a cost of $7.2 billion, and reached full commercial operation in March 2016. Its power station can produce 2,400 MW of electricity.
That pairing of power station and desalination plant sums up how the peninsula's people live with its geography: on a tilted block of desert with mountains at the edges, water is manufactured from seawater along the coasts, and the old oases of the interior survive on aquifers that are not being refilled.