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The Empty Quarter
In the winter of 2005-2006 the Saudi Geological Survey was in the midst of planning a major field excursion to the Saudi Arabian 'Empty Quarter' for numbers of its technical staff and invited outside experts. The field trip, which ran from February 25 to March 9, 2006 was a great success in giving the attendees a rich, varied, but quick overview of the vast region. The trip sparked interest in a  number of follow-up scientific projects in the region, some of which are now being considered as cooperative programs between SGS and external agencies.  
:: Overview of the Empty Quarter
:: Evolution and Structure
:: Flora and fauna
:: Population and infrastructure
:: Names of landmarks in the Empty Quarter
:: Importance of this region
:: Selected References
Overview of the Empty Quarter 
Sand deposits are widespread in the Kingdom of Saudi Arabia, particularly in the Arabian Platform, where they cover almost one-third of the total land area of the country.  The major sand seas of the Kingdom included An Nafud, in the north, Ad Dahna, in the east-central part of the Kingdom, and Al Jafurah in the east.  And of course, the largest of the Kingdom’s sand sea areas is the Rub al Khali, or Empty Quarter.  These sand units differ in their evolution, formation, shapes and colors.
Location and total area
The Empty Quarter (Ar-Rub al-Khali) lies in the southeastern part of the Arabian Peninsula. It covers almost a quarter of the total area of the Peninsula, and lies between long. 44°30''-56°30'E., and lat. 16°30'-23°00'N.  It is approximately 1200 km long and 650 km wide.  With a total area of 650,000 km2 , it is among the largest continuous deserts in the world.  About 80 percent of this area is in the Kingdom of Saudi Arabia, and covers about a quarter of the Kingdom's land surface. Its eastern edges extend into the United Arab Emirates, and its southern margin is in the Sultanate of Oman. Parts of its southern and southwestern limits are in the Republic of Yemen.

The region is almost empty of human beings due to the extreme heat, and scarce rain, vegetation, and water. Hence, in Arabic it is called 'Ar Rub al Khali' which means the Empty Quarter.  Moreover, its natural features of high sand dunes made it difficult for human life to survive and move around.  It is also known as the Great Sandy Desert.
The source of the name 'Ar Rub al Khali' is not exactly known. Some researchers say it is an old Arabian name used in the book of the famous Arabian seafarer Ibn Majid. The name of the book is 'Al-Fawa'id fii Osool Ilm al-Bihar wa al-Qa'wahid' (Benefits in the origins of Marine Science and Bases) where it was used to refer to places at the edge of Ma'rib and Al Jouf.  Other researchers say that the name was given by European explorers and orientalists who visited or attempted to cross the area.

Evolution and Structure 
The Empty Quarter is believed to have formed during pluvial and interpluvial periods in the Tertiary and Quaternary.  Former Aramco geologist Hal McClure said that the Empty Quarter was an alluvial valley created during the Paleocene epoch (over 65 million years ago) and confined to most of the Quaternary era; the sand dunes were formed during dry periods at the end of the Pleistocene (2 million years ago).
John Whitney (USGS) and others think that the sand dune areas in the Empty Quarter emerged from the end of the Miocene (25 million years ago) and up to the late Pleistocene.  The Empty Quarter represents a sedimentary basin that extends in the southeast, between the Al Hagar Mountains in the Sultanate of Oman; to the Zafar (Dhufar) and Hadhramaut highlands in the south, and to the As Sarawat Mountains and Tuwaiq Mountains, in the southwest, and north-northwest, respectively.
The Sand
Some experts say that there are two main sources for the sand seas in the Empty Quarter:
1--Continental sand transported by wadis flowing from Jibal al Hagar, Oman, Hadhramaut, Sarawat and Tuwaiq. The major wadis of this group that flow in the Empty Quarter basin are Wadi al Ain, Mowaitheel, Baladi, and Aswad, coming from the Al Hagar Mountains; Wadi Mighshin, Meetin, Jadeelah, Dhahiyyah, Armah, Hardha, Khadhrah, and Hazr, which come from Zafar and Hadhramaut; Wadi al Atfain, Waslah, Najran, and Habouna from Al Sarawat mountains; and Wadi al Ghar, and Al Hanu, which flow from the Tuwaiq Mountains. This is in addition to the sands coming from the Arabian shield, Oman Mountains, Hadhramaut, and Yemen Mountains. The sand is concentrated in southern, western, and northwestern parts of the Empty Quarter, and is characterized by its red color, a result of the presence of iron oxides.
2--Marine sands of the Arabian Gulf. These were formed by the continuous regressions of Arabian Gulf water during successive epochs. Then the sands were moved by the winds to the Empty Quarter basin. These sands are characteristically white, coarse, salty, and easy to move. They are concentrated in the eastern, and the northeastern parts of the Empty Quarter. Al Gafourah sands represent an ideal source of marine sand of the Empty Quarter.
The wind plays a major role in forming and shaping the sands of the Empty Quarter. The area slopes generally from the west to the east and northeast at a rate of 1 m per km. The average height above sea level of the sands in the western and southwestern parts of the area ranges between 900-1000 m.
The average height in the middle of the Empty Quarter is 400-500 m, and in the eastern and northeastern fringe it is 100-150 m a.s.l. Elevations decrease as one moves towards the Arabian Gulf.
The Empty Quarter can be divided into 5 sections based on the types of its Dunes:
1. Barchan dunes: These are high and large dunes often hosting moist sabkha interspersed among them. Some dunes can reach as much as 150-200 m in height.  Most of these are in the northeastern part of the area, such as the obstructive 'uruqs, which are sinuous, elongate, sand ridges, many kilometers in length, and the 'uruqs at Ash Shaibah.
2. Star dunes: These dunes have steep pyramidic shapes, and steep tops, and are formed individually or as interstructural shapes.  In some areas, they can reach as much as 200 m in height.  They occur in the southern and eastern parts of the Empty Quarter.  Examples are the Al G'ad and Ghonaim sand dunes.
3. Domal dunes: These dunes have the characteristic of being high and interstructured. They represent the junction of longitudinal dunes that run in opposite directions. Some domal dunes reach as much as 100 m in height.  They can be found in the middle of the Empty Quarter. The most famous are Al Hibak, Al Hawayah and Al Gama'eer sand hills.
4. Sand sheets: These form semi-flat to wavelike sand cover, and include sand hills and low hills such as As Sanam and Al Galdah.

5. Longitudinal dunes: These are long 'uruqs of sand that extend, in parallel formation, between the southwestern and northeastern parts of the Empty Quarter; segments may reach up to 100 m in height. Typical dunes of this type are represented by Al Gha'amiyat, Maghdarat, Al Awrak, Bani Ma'aridh, Bani Humran, and Al Majari. The dunes are spread extensively over the western part of the Empty Quarter.

Flora and fauna 
Plant life exists in the Empty Quarter, and in places can be good for grazing. In some areas plants can grow thick despite the scanty rains.
There exist plants that have local names such as Al-Abal, Al-Haram, As-Shinan, Az- Zahar, Al-Andab, Al- Alqa, Al-Burkan, and Al-Ghadha; these are seasonal and resistant to drought for relatively long periods. The vegetation, in earlier periods, allowed parts of the Empty Quarter to be a refuge for a number of large animal species. Until recently, Arabian oryx, ostrich, sand tigers, and other species were known in the region, but they are now gone, possibly from drought or hunting.
The National Commission for Wildlife Conservation and Development in the Kingdom of Saudi Arabia established a wildlife park in the southwestern edge of the Empty Quarter, at 'Uruq Bani Ma'aridh. The total conservation area is 12,000 km2. It lies south of As Sulayyil and east of Jabal Tuwaiq. It is intended as a resettlement location for animals previously in this area, such as the Arabian oryx and reem gazelle. It is also meant to protect local plants from unregulated grazing and cutting.

The Empty Quarter has many ancient wells and water sources. These sources are relatively plentiful in the eastern, northeastern, and northern parts of the area due to the relative nearness of groundwater. The main sources of water are:
Artesian wells with sulfurous water dug by Aramco during its survey and exploration activities. The wells are scattered over most parts of the area.
Gorges containing brackish water, spreading in the eastern part of the Empty Quarter.  Such water is near to the surface.
Wells: these contain water that is somewhat potable. The local inhabitants and shepherds cover the tops of these wells after using them to avoid sand dumping. They are well marked for their use when needed.
Famous water sources in the Empty Quarter are: B'ir Al Shalfa'a, B'ir Fadil, ‘Ayn Humaidan, B'ir Owbar, Galmat Al Juhaish, B'ir Hadi, B'ir al Towairgiyah, Galmat al Harsha'a, B'ir ath Thuwairah, Galmat Mahoula (The Triangle), Abar Ma'amourah, B'ir Umal Hadeed, B'ir Faisal, B'ir Faris, Galmat Ummahat Borkan, Galmat Uwairkrah, Galmat at Taweelah, Galmat Hamraa Natheel, Galmat Um Shaddad, B'ir al Gidairat, Galmat al Abellah, Galmat al Hafra, B'ir Taweelat Hadi, among others.
The Kingdom established laboratories for water technology of some artesian wells dug at inhabited centers in Ash Sharourah, Alwadee'ah, Al Kharkheer, Ardah, As Samhah, Zaabalutin, and Shabeetah, and in the border guard centers close to neighboring countries.  The Ministry of Water has a project that is underway to dig wells in Al Nigaha'a in the Empty Quarter east of Najran to draw and purify water for Najran city.

Population and infrastructure 
The Empty Quarter is inhabited by a number of tribal populations, the best known being the Yam, Al-Murrah, Ad Dawasir, Ar Raswashid, Al Manaheel, and Al Say'ar.
The largest settled population centers in the Empty Quarter and its periphery are in Najran, Al Wadee'ah, Ash Sharourah, Al Akha'sheem, Khabash, Al Mankhali, Tamani, Zalma, Al Hassa, Al Gadeed, Raidah, As Sulayyil, Yibreen, Ardah, As Samha, Za'balutin, and Al Kharkheer.  A number of significant archeological locations, such as Najran, Al Fau, Yibreen, Awbar, and other localities can be found along the perimeter of the Empty Quarter.
Some paved and dirt roads traverse the Empty Quarter and its margins. These roads were constructed to link the population centers, frontier stations, water resources and oil production centers with adjacent towns.
The paved roads include:
1.-A paved road constructed by Saudi Aramco in the northeast of the Empty Quarter to link Ash Shaibah oil field to major highways in the east, and to Aramco headquarters in Dhahran.
2.-A paved road (under construction) that links Ash Sharourah to Al Kharkeer through the centers of Sultanah and Al Akhasheem.
Unpaved roads that cross the Empty Quarter include:
1.-A road in the central Empty Quarter linking Al Kharkeer to Haradh and Yabreen through Galmat Nadgan, Al Abeilah, B'ir Faisal and B'ir Hadi.
2.-A road that forks off the Ash Shaibah road and joins the road described above, near Al Ebailah.
3.-A road linking Najran with the northwestern margins of the Empty Quarter up to Raida and Al Hassy, Al Jadeed and As Sulayyil.
4.-A road extending from Ash Shaiba, along the Saudi border with the UAE and Oman, linking Ardah, Za'abalutin and Al Kharkheer in the Eastern Region.
There are airports and airstrips at some of the population centers around and at the margins of the Empty Quarter such as the Najran and Ash Sharourah commercial airports, and the asphalted airstrips at As Sulayyil, Za'abalutin, Ardah, Shibailah, and Ash Shaibah.  In addition to these, there are dozens of earthen airstrips scattered over the central part of the Empty Quarter, constructed by Saudi Aramco for its survey and exploration operations.

Names of landmarks in the Empty Quarter 
The Empty Quarter remained unknown for long periods of time, and in particular its more remote parts, because of its vast area and difficult climatic conditions, and its rugged terrain and largely unknown resources. Consequently, visits to the area were few, and roads and other infrastructure were largely absent.  As a result there are few named landmarks. Such names as do exist are mostly limited to major landforms, and sources of water.  Due to the general uniformity of many features found in the Empty Quarter, most named locations are derived from the shapes and forms of those features.  Sometimes locations are named for plant types known to exist there or are related to events that occurred there, or the tribes that live there, or the names of wadis.
The most famous landmarks in the east of the Empty Quarter are: 'Uruq ash Shaibah, Al Kadan, Al 'Uruq al Mu'taridah, Al Manadir, Al Qu'od and Ghunaim; to the west, the best known named landmarks are: Al Mahakik, Al Habak, Ad Dikakah and Al Hawaya; to the north: As Sanam and Az Zufrah; to the northwest: 'Uruq al Majari, Bani Humran and Bani M'arid; to the south: Uruq al Awrak, Al Jildah, 'Umahat Maru and Maghdrat.
In the western part of the Empty Quarter there are numerous depressions between the sand dunes.  These extend long distances between linear dunes and are often named.  For example, they are called Najran, Al Ajashir, Al Khareetah, Al Esharat, Al Bakrah, Al Kanawir, Umahat Joudan and Al Ma'ateef, etc.  Commonly, the names for these depressions are better known in the region than the names of the adjacent linear dunes.
Importance of this region 
Entering and crossing the Empty Quarter is not an easy task.  Few outsiders managed to do it other than a handful of orientalist explorers who were accompanied by experienced tribal guides with good knowledge of its tracks, trails, and resources.  Among such explorers were: D.E. Cheeseman in 1923, Burtram Thomas in 1930, Abdullah Philby in 1932, and Wilfred Thesiger (Mubarak Bin London) in 1945.
At the beginning of the 20th century the Empty Quarter began to attract the attention of the countries across which it lies; thus research and exploration was carried out to identify its natural resources.  Petroleum and gas were discovered in the UAE and Oman. In Saudi Arabia, Aramco carried out survey and exploration operations for petroleum and gas throughout the Empty Quarter. These two commodities were found in commercial quantity in a number of areas, such as the large Ash Shaibah petroleum field.
During the period 1979-1982 the Aerial Survey Department of the Saudi Arabian Ministry of Petroleum and Mineral Resources established a geodetic network covering most parts of the Empty Quarter and which is currently part of the national geodetic network. This was followed by the production of topographic maps based on aerial photos covering the entire Empty Quarter at a scale 1:100,000 from which maps at smaller scales were produced to serve the purposes and needs of different agencies in the Kingdom.
Following demarcation of the international boundaries between the Kingdom and neighboring countries, which include many kilometers within the Empty Quarter (with the UAE, Sultanate of Oman, and Arab Republic of Yemen), a number of Saudi population centers near the border have grown and expanded considerably, such as the town of Ash Sharourah (Najran Region).  Other centers were also established along the border with Oman, such as Aradah, As Sahmah, and Za'abulutin (Eastern region).  A number of Saudi Frontier Guard posts and stations were also established along the length of the international boundary.  In addition, entry points were established on the border with Yemen such as at Al Khadra and Al Wadi'aa (Najran region).
In April 1968 the huge Ash Shaibah oilfield was discovered close to the border with UAE.  Saudi Aramco started production at that field in July 1998. The Kingdom announced investment opportunities for exploration of non-associated gas in the Empty Quarter.  Partnership agreements were signed between Saudi Aramco and a number of international companies for non-associated gas exploration and exploitation at various localities in the Empty Quarter.
In addition to oil and gas, the Empty Quarter contains other resources that have not been exploited up to now, including localities containing abundant water, dense sands, extensive sabkhas and archeological sites, which may have touristic potential.
Selected References 
• Al-Walee'ie Abdallah bin Nasir, 1417 A. H. (1997); Sand seas in the Kingdom of Saudi Arabia.
• Clark, A., 1989, Lakes of the Rub’ al Khali, in Saudi Aramco World, vol. 40, 3, p. 28-33.
• Edgell, H.S., 2006, Arabian Deserts: Nature, Origin, and Evolution, Springer, 261 p.
• Ministry of Petroleum and Mineral Resources, Aerial Survey Department, 1406-1414 A.H. (1986-1993).
• Saudi Geological Survey: Field trips 1423-1426 A.H. (2003-2005.)
• Whitney, J.W., Faulkender, D.J., and Rubin, M., 1983, The environmental history and present condition of Saudi Arabia’s northern sand seas: U.S. Geological Survey Open-File Report 83-749.