Lake is a body of water surrounded by land. Lakes may be found in all parts of the world. Some large bodies of water commonly known as seas are really lakes. These include the Dead Sea, the Sea of Galilee, and the Caspian Sea. Some lakes lie near the highest regions of Earth, and others are far below sea level. Lake Titicaca, in South America, is 12,507 feet (3,812 meters) above sea level. The Dead Sea, between Israel and Jordan, lies about 1,411 feet (430 meters) below sea level. The word lake comes from a Greek word meaning hole or pond.
The life of a lake
How lakes are formed.
The greatest number of lakes lie in regions that were once covered by glaciers. In mountainous regions, glaciers carved deep valleys as they traveled. The basins they carved then filled with water to form lakes. In nonmountainous regions of North America and northern Europe, glaciers gouged hollows in the land and deposited rocks and earth as they melted. Many lakes formed in these hollows and in the uneven land created by glacial deposits. The action of glaciers explains why there are more lakes in the northern part of the United States than in the southern part. Minnesota has about 11,000 lakes formed by the action of glaciers. The Great Lakes were formed partly by glacial action.
Other areas that abound in lakes are regions lying on limestone bedrock, such as the Florida peninsula in the Southern United States. More than 1,400 lakes and ponds lie in Lake County, Florida. In a limestone region, underground water slowly dissolves the limestone rock. This action begins in cracks in the rock and continues until the surface collapses, forming a pit known as a sinkhole. The sinkhole may then fill with water and become a lake or a pond.
Sinkholes may be 60 feet (18 meters) or more deep. They sometimes lie in the course of a fast-flowing underground stream. In such cases, the sinkhole fills quickly, forming a beautiful pool of crystal-clear water. The uplands region of northern Florida has many of these “springs,” as they are known locally. The largest and best known is Silver Springs.
Lakes may also form in a number of other ways. The natural collection of rainwater in the craters of extinct volcanoes can create lakes. Crater Lake in Oregon was formed in this manner. Lake basins can be created by movements in Earth’s crust known as faulting. Lake Baikal in Russia, the world’s deepest lake, was formed this way. Lakes may appear when rivers deposit silt until the natural outlet to the sea is closed, and the water backs up. Dam construction creates great artificial lakes that are called reservoirs. The lake behind the dam in Kariba Gorge, on Africa’s Zambezi River, is more than 175 miles (282 kilometers) long.
How lakes are fed.
Rivers and mountain streams feed some lakes. Other lakes do not appear to have any water coming into them. They are actually fed by underground springs or streams. Still other lakes have inlets but no outlets. For example, the Great Salt Lake in Utah does not have any streams running out of it.
How lakes disappear.
The lakes that now exist will probably disappear in time. Some lakes dry up because of a change in climate or because of a change in the course of the waters that feed them. A bursting volcano or earthquake may change the surface of the surrounding region and cause lakes to disappear. In addition, lakes may drain into other bodies of water and vanish.
Ground water fills the sinkholes in limestone areas. A long drought in such areas can completely dry up lakes and ponds in sinkholes. A seepage outlet in a sinkhole may also cause a lake to disappear by draining the water into an underground cavern. Many low-lying regions on Earth’s surface are the basins of lakes that no longer exist. Small lakes can be filled in by deposits of mud, sand, and silt. These materials may form excellent soils.
The lake habitat.
Lakes create little worlds of their own. Water plants live under the surface of lakes. Some of the plants are attached to the lake bottom, and others float free. This vegetation provides food for water creatures such as water insects, snails, turtles, and fish. Lakes are also a habitat for waterfowl such as ducks, geese, swans, flamingos, egrets, cranes, and others. Land animals use lakes for drinking water. They also obtain food from lakes.
The importance of lakes
Climate.
The presence of large lakes in a region greatly influences the lives of the people living nearby. Lakes affect weather conditions over a large area. In summer, a lake never gets as warm as the surrounding land. Thus, breezes blowing over the water are cooled. In winter, a lake does not cool off as fast as the surrounding land, and may cause the climate to be warmer.
Warm winds blowing off a lake in autumn make it possible for certain crops to grow especially well. The warming influence of Lake Ontario in autumn extends the growing season of southern Ontario, making it possible to raise fruits and corn. The great fruit belt of Michigan, along the east shore of Lake Michigan, depends partly on winds off the lake. Cool spring winds delay the blossoming of the fruit trees until the danger of a killing frost has passed. Warm winds in autumn allow the fruit crops to be harvested before the frost strikes. The thousands of lakes in central Florida have an important effect on the location of the state’s citrus-fruit industry. Careful studies have shown that these lakes help reduce the damaging effects of cold spells that might cause great loss to fruitgrowers.
Travel and trade routes.
The growth of travel and commerce on the Great Lakes provides a typical example of people’s use of lakes. The early explorers of North America used lakes and their connecting rivers as their chief travel routes. Some of these explorers paddled canoes up the St. Lawrence River to the Great Lakes.
Steamboats took the place of canoes in the 1800’s. Today, freighters, tugboats, and barges work their way along inland navigation routes on the Great Lakes, carrying raw materials to the industrial cities that are located along the lakes. Products carried on the Great Lakes include coal, iron ore, and grain.
Irrigation.
Lakes provide an important source of water for irrigation. Water may be fed from the lakes to farmers’ fields by ditches or canals, or it may be pumped into an overhead system of sprinklers. People have built huge dams on rivers in desert areas to create reservoirs of water for irrigation. The Egyptians built the Aswan High Dam on the Nile River partly for this purpose. The dams on the Indus River provide water to irrigate 361/2 million acres (14.8 million hectares) of desert land. These irrigated regions, which lie mainly in Pakistan, supply food for millions of people.
Water supply
has been a serious problem ever since people started to live in towns and cities. Lakes offered a natural reservoir of water for early communities. But most cities today have outgrown such natural supplies, and people have built huge storage dams in order to provide additional water. The reservoirs formed by these dams sometimes lie far away from the city. For example, New York City uses water from the Catskill Mountains, which are located more than 100 miles (160 kilometers) away.
Hydroelectric power.
Lakes created as storage reservoirs can be used to generate electric power. To produce electric power, hydroelectric power plants make use of the force of water falling from the dam to the river below.
Recreation.
People use lakes for a variety of recreational activities. They flock to lakes to enjoy fishing, boating, swimming, water-skiing, and ice skating. In such states as Florida, the freshwater recreational industry provides millions of dollars of income every year.
