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.

oasis
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.

Noun

an underground layer of rock or earth which holds groundwater.

arid
Adjective

dry.

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.)

Noun

agricultural produce.

date palm
Noun

type of fruit tree.

delicate
Adjective

fragile or easily damaged.

Noun

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

Noun

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

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

corn.

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.

Noun

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

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.

Noun

large stream of flowing fresh water.

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.