• An oasis is an area made fertile by a source of freshwater in an otherwise dry and arid region. Oases (more than one oasis) are irrigated by natural springs or other underground water sources. They vary in size from a cluster of date palms around a well or a spring to a city and its irrigated cropland. Dates, cotton, olives, figs, citrus fruits, wheat and corn (maize) are common oasis crops.

    Underground water sources called aquifers supply most oases. In some cases, a natural spring brings the underground water to the surface. At other oases, manmade wells tap the aquifer. In some oasis settlements, these wells might be centuries old and might have been diligently maintained for generations to preserve access to their life-giving water.

    Sands blown by desert winds threaten wells as well as agricultural areas in oases. Sand can destroy crops and pollute water. Communities have traditionally planted strong trees, such as palms, around the perimeter of oases to keep the desert sands from their delicate crops and water.

    Some of the world's largest supplies of underground water exist beneath the Sahara Desert, supporting about 90 major oases there. The Sahara is the largest desert on Earth—about the size of the continental United States. Though there are many oases there, traveling between them can take days because the desert is so vast.

    For this reason, oases in the Sahara and throughout the world have become important stops along trade routes. Merchants and traders who travel along these routes must stop at oases to replenish food and water supplies. This means that whoever controls an oasis also controls the trade along the route—making oases desirable to political, economic, and military leaders.

    Al-Hasa, Saudi Arabia, has been an important farming area for the Arabian Peninsula for thousands of years. Today, it continues to be a leading agricultural region, producing dates, rice, corn, sheep, cattle, and eggs. The al-Hasa region also lies above one of the richest oil fields in the world, making the oasis an important center of international trade.

    Rivers that flow through some deserts provide permanent sources of water for large, elongated oases. The fertile Nile River valley and delta in Egypt, supplied with water from the Nile River, is an example of this type of large oasis. At 22,000 square kilometers, it might be the largest oasis in the world.

    The palm trees of this oasis signal the presence of water in the middle of the Sahara.

    Meadow in the Mojave
    The Las Vegas Valley, in the U.S. state of Nevada, is a popular tourist destination known for gaming and entertainment. Before the arrival of casinos, however, Las Vegas was the site of a natural oasis in the Mojave Desert. Springs brought water from the regions aquifer to the surface, ultimately flowing into the Colorado River. Las Vegas means the meadows in Spanish, and was named when the oasis was discovered by Mexican merchants in 1829.

    The Las Vegas oasis has dried up. Development drained the springs. The areas empty aquifers are now used to store water from Lake Mead, an artificial lake created by the Hoover Dam on the Colorado River. Water is a major environmental and political issue in Las Vegas and throughout the U.S. Southwest.

  • Term Part of Speech Definition Encyclopedic Entry
    aquifer Noun

    an underground layer of rock or earth which holds groundwater.

    Encyclopedic Entry: aquifer
    arid Adjective


    casino Noun

    building filled with equipment and games for gambling.

    century Noun

    100 years.

    citrus Noun

    type of fruit tree, including lemon and orange.

    cluster Noun

    group of organisms or objects that share at least one characteristic.

    Colorado River Noun

    (2,335 kilometers/1,450 miles) river in the western U.S. and Mexico, draining into the Gulf of California.

    continental United States Noun

    U.S. land continuously stretching from the Atlantic to Pacific oceans (not including the states of Alaska and Hawaii.)

    crop Noun

    agricultural produce.

    Encyclopedic Entry: crop
    date palm Noun

    type of fruit tree.

    delicate Adjective

    fragile or easily damaged.

    delta Noun

    the flat, low-lying plain that sometimes forms at the mouth of a river from deposits of sediments.

    Encyclopedic Entry: delta
    desert Noun

    area of land that receives no more than 25 centimeters (10 inches) of precipitation a year.

    Encyclopedic Entry: desert
    development Noun

    construction or preparation of land for housing, industry, or agriculture.

    diligently Adverb

    hardworking and consistent.

    economic Adjective

    having to do with money.

    fertile Adjective

    able to produce crops or sustain agriculture.

    freshwater Noun

    water that is not salty.

    gaming Noun

    industry surrounding games of luck and skill in which players use their own money or goods to have a chance to win more. Also called gambling.

    generation Noun

    group in a species made up of members that are roughly the same age.

    Hoover Dam Noun

    dam on the Colorado River between the U.S. states of Arizona and Nevada. Also called the Boulder Dam.

    international Adjective

    having to do with more than one country.

    irrigate Verb

    to water.

    Lake Mead Noun

    (588 square kilometers/227 square miles) lake formed by the Hoover Dam in the U.S. states of Arizona and Nevada.

    maize Noun


    merchant Noun

    person who sells goods and services.

    military Noun

    armed forces.

    Mojave Desert Noun

    arid landscape in the U.S. states of California, Arizona, Nevada, and Utah.

    Nile River Noun

    (5,592 kilometers/3,473 miles) river in East Africa.

    oasis Noun

    area made fertile by a source of fresh water in an otherwise arid region.

    Encyclopedic Entry: oasis
    oil field Noun

    region with a large number of oil wells or other extractive technologies.

    perimeter Noun

    outline or border.

    permanent Adjective

    constant or lasting forever.

    pollute Verb

    to introduce harmful materials into a natural environment.

    rainfall Noun

    amount of precipitation that falls in a specific area during a specific time.

    replenish Verb

    to supply or refill.

    river Noun

    large stream of flowing fresh water.

    Encyclopedic Entry: river
    Sahara Desert Noun

    world's largest desert, in north Africa.

    sand Noun

    small, loose grains of disintegrated rocks.

    spring Noun

    small flow of water flowing naturally from an underground water source.

    trade Noun

    buying, selling, or exchanging of goods and services.

    trade route Noun

    path followed by merchants or explorers to exchange goods and services.

    vast Adjective

    huge and spread out.

    well Noun

    a hole drilled in the Earth to obtain a liquid or gaseous substance.

    wind Noun

    movement of air (from a high pressure zone to a low pressure zone) caused by the uneven heating of the Earth by the sun.