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In geography, an oasis (plural: oases) or cienega (Southwestern United States) is an isolated area of vegetation in a desert, typically surrounding a spring or similar water source. Oases also provide habitat for animals and even humans if the area is big enough. The location of oases has been of critical importance for trade and transportation routes in desert areas. Caravans must travel via oases so that supplies of water and food can be replenished. Thus, political or military control of an oasis has in many cases meant control of trade on a particular route. For example, the oases of Awjila, Ghadames and Kufra, situated in modern-day Libya, have at various times been vital to both North-South and East-West trade in the Sahara.
Oases are formed from underground rivers or aquifers such as an artesian aquifer, where water can reach the surface naturally by pressure or by man made wells. Occasional brief thunderstorms provide subterranean water to sustain natural oases, such as the Tuat. Substrata of impermeable rock and stone can trap water and retain it in pockets, or on long faulting subsurface ridges or volcanic dikes water can collect and percolate to the surface. Any incidence of water is then used by migrating birds who also pass seeds with their droppings which will grow at the water's edge forming an oasis.
The word oasis comes into English via Latin: oasis from Ancient Greek: ὄασις óasis, which in turn is a direct borrowing from Demotic Egyptian. The word for oasis in the later attested Coptic language (the descendant of Demotic Egyptian) is wahe or ouahe which means a 'dwelling place'.
Growing plants 
People who live in an oasis must manage land and water use carefully; fields must be irrigated to grow plants like dates, figs, olives, and apricots. The most important plant in an oasis is the date palm, which forms the upper layer. These palm trees provide shade for smaller trees like peach trees, which form the middle layer. By growing plants in different layers, the farmers make best use of the soil and water. Many vegetables are also grown and some cereals, such as wheat, barley and millet, are grown where there is more moisture.
Notable oases 
- Nile River valley and delta, Egypt, is claimed as the world's biggest oasis by the 2007 edition of The Guinness Book of World Records with a stated area of 22,000 square kilometres.
- Bahariya Oasis, Egypt
- Dakhla Oasis, Egypt
- Farafra Oasis, Egypt
- Gaberoun, Libya
- Jalu, Libya
- Kharga Oasis, Egypt
- Kufra Oasis, Libya
- M'Zab Valley, Algeria
- Ouargla, Algeria
- Siwa Oasis, Egypt
- Tafilalt, Morocco
- Timimoun, Algeria
- Tozeur, Tunisia
- Tuat, Algeria
North America and South America 
- Fish Springs National Wildlife Refuge, United States
- Huacachina, Peru
- La Cienega, New Mexico, a paraje on El Camino Real de Tierra Adentro, United States
- Las Vegas Valley, Nevada, United States, what was once an oasis in the vast Mojave desert has over the years grown into a metropolitan area.
- Mulege, Baja California Sur, Mexico
- San Ignacio, Baja California Sur, Mexico
- Twentynine Palms, California, United States
- Warm Springs Natural Area, United States
- Al-Hasa,The largest in Asia, Saudi Arabia.
- Al-Qatif, Saudi Arabia, large oasis on the coast of the Persian Gulf.
- Azraq, Jordan
- Ein Gedi, Israel
- Liwa Oasis, United Arab Emirates
- Loulan, China
- Miran, China
- Niya, China
- Tabas, Iran
- Turpan, China
- Yarkand, China
See also 
- Great Manmade River – World's largest irrigation project developed in Libya connecting cities with fossil water
- (French) référence: Jardins au désert (Vincent Battesti)|Battesti (Vincent), Jardins au désert, Evolution des pratiques et savoirs oasiens, Jérid tunisien, Paris, Éditions IRD, coll. À travers champs, 2005, 440 p. ISBN 2-7099-1564-2 Open Archives: book in free access / in French
|Wikimedia Commons has media related to: Oases|
- The dictionary definition of oasis at Wiktionary