Deserts
... withstand long dry periods. Most desert plants have thick bark and waxy leaves to help them save water. Those like the cactus have thorns for protection against animals. In some deserts underground springs or rivers provide water for more luxuriant vegetation. A place in the desert that has enough water for dense plant growth is called an oasis. It looks like a green island in a sea of desert. Some basins in the dry deserts have no outlets to an ocean. The meager rainfall flows from surrounding uplands, carrying minerals that have dissolved from the soil and rock. If there is enough water, it collects to form salt lakes. Great Salt Lake in Utah and the Caspian Sea on the border between Europe and Asia are examples of large desert salt lakes. Most salt lakes are much smaller. Evaporation causes them to dry up soon after a flood, leaving the minerals behind. These temporary lakes are called playas. The soils of these dry lakebeds are too salty for most plants. Cold deserts Like the hot, dry deserts, the cold deserts have little plant life and few people. The hot deserts are deserts of drought. Low temperatures cause the cold deserts. The deserts of the Arctic are not as cold as the Antarctic ice cap, but the winters are long, dark, and very cold. The summers are bearly warm enough for a few lichens, mosses, and grasses to grow. Even in the warmer parts of the cold deserts the ground is frozen for most of the year. The soil thaws only at the surface and on sunny slopes. Snow is never very deep except on permanent ice caps and where it has been drifted by the wind. Rainfall is light in the warmer months. Water is slow to evaporate in the cool air, and does not sink deeply into the frozen soil. That is why parts of the cold deserts are swampy in summer. The oases of the cold deserts are the patches of tundra grasses that grow in sheltered spots among the stretches of bare rock, gravel, or snow. Since there are not many plants for food, the number of animals is also small. Musk oxen and caribou sometimes graze in the desert tundra. There are also wolves, foxes, Arctic hares, and mouselike lemmings. Many birds choose the cold deserts for their summer breeding grounds. A few, such as the ptarmigan and the snow bunting, stay all winter. Importance of the deserts No matter how dry a desert may be, it is not necessarily worthless. In some of the driest regions people have found valuable minerals. The manufacture of salt is one of the industries at Great Salt Lake in Utah. In the Atacama Desert of Chile, nitrates are mined for use in industry and fertilizer taken from salt deserts. Borax comes from Death Valley in California. Underground in the deserts are many of the same minerals that are found in other parts of the world. Copper comes from mines in the Atacama Desert and in Arizona and Utah. In the past, discoveries of gold or silver set of rushes of prospectors and miners to the deserts of the western United States. A few gold-mining centers like Kalgoorlie in western Australia have produced gold for many years. Uranium ore is mined on the Colorado Plateau in the southwestern United States. The Namib Desert of southwestern Africa is a leading source of diamonds. The discovery of petroleum has brought great changes to the deserts. Oil is the most important export of several desert countries in the Middle East and North Africa. This valuable resource has made such countries very wealthy. The cold desert of northern Alaska is also a source of oil and natural gas. Pipelines carry the petroleum from wells in the desert to refineries and ports. From there it is shipped to other nations in huge tankers. Desert animals There are many animals in the desert. Some are very large, like the kangaroo or the gazelle. Both are big and have to travel long distances for water at a spring, or an oasis. Camels are also extremely big. They have one or two humps used for storing water and food. For this reason camels need very little water. People of the desert often used camels as transportation. Another fairly large animal is the addax. The addax is a desert antelope. They live in the Sahara Desert. All addaxes are herbivores. There are less than 200 of them left because of hunting and tourists. Some animals slither or crawl along. Examples of these are snakes and lizards. Snakes rarely drink water; they get their moisture from other prey that they eat. So do others, like the kangaroo rat. Lizards are commonly found in the desert. They stay out of the sun and move as little as possible. There are also other animals in the desert. ...