Landforms and Landscapes

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Landforms and Landscapes For Years 6-8

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Antarctica

The icy continent surrounding the South Pole is called Antarctica. Its name means “opposite to the Arctic,” referring to the region around the North Pole. Antarctica is the fifth in size among the continents, larger than Europe and Australia. It is a cold and forbidding land that has no permanent human population and is almost devoid of animal or plant life. However, the ocean surrounding Antarctica teems with life.

A map of Antarctica highlights the major geographic regions, ice sheets, and research stations (with …

Encyclopædia Britannica, Inc.

Gentoo penguins live in Antarctica.

Paul Souders—Stone/Getty Images

Researchers study the Ross Ice Shelf at the Bay of Whales, Antarctica.

Michael Van Woert/NOAA NESDIS, ORA

Ice and stormy seas kept anyone from seeing Antarctica until about 1820. In 1950 more than half the continent still had not been seen. Now airplanes and tractors have taken people to most parts of Antarctica, and satellite photographs have revealed the rest. But Antarctica remains a frontier, and much is yet to be learned about it.

Almost no one goes to Antarctica except scientists and some adventurous tourists. The continent has natural resources that someday may be used, but the harsh environment of the area makes them difficult to exploit. Countries interested in Antarctica have signed a treaty that reserves the region for science and other peaceful purposes.

The Land

Paradise Bay is a harbor on the Antarctic Peninsula.

Antarctica covers an area of about 5.5 million square miles (14.2 million square kilometers). It would be essentially circular except for the Antarctic Peninsula and two indentations created by the Ross Sea and the Weddell Sea. The Antarctic Peninsula forms an 800-mile (1,300-kilometer) northward extension of Antarctica toward the southern tip of South America, about 600 miles (970 kilometers) away.

The enormous Beardmore Glacier extends across the Transantarctic Mountains of central Antarctica.

Commander Jim Waldron USNR—Antarctic Photo Library/National Science Foundation

An ice sheet covers nearly all of Antarctica. At its thickest point the ice sheet is 15,670 feet (4,776 meters) deep—almost 3 miles (5 kilometers). It averages 7,000 to 8,000 feet (2,100 to 2,400 meters) thick, making Antarctica the continent with the highest mean elevation. This ice sheet contains 90 percent of the world’s ice and 70 percent of the world’s fresh water.

An iceberg floats in the waters off Antarctica.

iStockphoto/Thinkstock

This picture shows the edge of an ice shelf in Antarctica. An ice shelf is a thick mass of floating…

The Antarctic ice was formed from the snows of millions of years that fell on the land, layer on layer. The weight of new snow squeezes the old snow underneath until it turns to a substance called firn, then ice. As the ice piles up, it moves toward the coast like batter spreading in a pan. The moving ice forms into glaciers, rivers of ice that flow into the sea. Pieces of the floating glaciers break off from time to time, a process called calving. These icebergs float north until they reach warm water, break into pieces, and melt. Icebergs as large as 40 by 30 miles (64 by 48 kilometers) have been sighted, but most are smaller. In some places the floating glaciers stay attached to the land and continue to grow until they become ice shelves. The Ross Ice Shelf alone is about the size of Canada’s Yukon Territory and averages 1,100 feet (330 meters) thick.

The Transantarctic Mountains divide Antarctica into eastern and western parts. The mountains stretch …

Hannes Grobe

The Transantarctic Mountains extend for more than 2,000 miles (3,200 kilometers) across the continent, dividing the ice sheet into two parts. The larger, eastern part—called East Antarctica—rests on land that is mostly above sea level. It has been there at least 14 million years. The smaller, western part—called West Antarctica—is on land that is mostly below sea level.

Other mountain ranges include the Prince Charles Mountains and smaller groups near the coasts. The Antarctic Peninsula has many mountains. The Ellsworth Mountains are Antarctica’s highest, the Vinson Massif rising 16,050 feet (4,892 meters) above sea level. Mountains with only their peaks showing through the ice (called nunataks) are found in some areas. Several active volcanoes on the continent provide spectacular and scenic landforms at many places and are located near the Antarctic Peninsula and in the Transantarctic Mountains.

Only about 2 percent of Antarctica is free from ice. These unusual land areas, called oases, generally are near the coast and include the dry valleys of southern Victoria Land and the Bunger Oasis in Wilkes Land. High rims at the end of the valleys prevent entry of large glaciers. The warm local climate melts the ends of smaller glaciers extending into the valleys.

Surrounding Antarctica is a cold water mass called the Southern, or Antarctic, Ocean. It contains what were once considered the southern parts of the Pacific, the Atlantic, and the Indian oceans. The Ross and Weddell seas are extensions of the Southern Ocean. The Antarctic Convergence, which encircles Antarctica roughly 1,000 miles (1,600 kilometers) off the coast, divides the cold southern water mass from warmer waters to the north. The Antarctic Circumpolar Current, the world’s largest ocean current, moves eastward around the continent at an average speed of about half a knot (1 kilometer per hour). Sea ice up to 10 feet (3 meters) thick forms outward from the continent every winter, making a belt 300 to 1,000 miles (500 to 1,600 kilometers) wide. Even in summer the sea ice belt is 100 to 500 miles (160 to 800 kilometers) wide in most places.

The aurora australis, or southern lights, glow in the skies over Antarctica in winter.

Antarctica has three points that are called South Poles. The best known is the geographic South Pole, at 90° S latitude on the axis of Earth’s rotation. In the early 1990s the geomagnetic South Pole, which moves, was located at about 78° S, 108° E, in East Antarctica; it is the center of the Southern Hemisphere auroras. The magnetic South Pole is the area toward which compasses point; it is just off the Adélie Coast at about 66° S, 139° E, and moves a few miles to the northwest each year.

Antarctica does not have 24-hour periods broken into days and nights. This is because the continent lies almost entirely south of the line of latitude of 66.5° S, which is known as the Antarctic Circle. Because of the tilt of Earth’ s axis as it revolves around the Sun, the Antarctic Circle has one day each year when the Sun does not set (the summer solstice, December 21 or 22) and one day when the Sun does not rise (the winter solstice, June 21 or

22). The number of days without sunset or sunrise increases southward from the Antarctic Circle. At the South Pole the Sun rises on about September 21 and moves in a circular path upward until December 21, when it reaches about 23.5° above the horizon. Then it circles downward until it sets on about March 22. This “day,” or summer, is six months long. From March 22 until September 21 the South Pole is dark, and Antarctica has its long “night,” or winter.

According to scientific theory, some 200 million years ago Antarctica was joined to South America, Africa, India, and Australia in a single large continent called Gondwana. There was no ice sheet, and trees and large animals flourished. Today, only geological formations, coal beds, and fossils remain as clues to Antarctica’s warm past. Climate

Antarctica is the coldest continent. The world’s record low temperature of –128.6 °F (–89.2 °C) was recorded there. The mean annual temperature of the interior is –70 °F (–57 °C). The coast is warmer. Monthly mean temperatures at McMurdo Station range from –18° F (–28 °C) in August to 27 °F (–3 °C) in January. Along the Antarctic Peninsula temperatures have been as high as 59 ° F (15 °C).

A person walks in the wind at a camp in Antarctica.

FLPA/SuperStock

Because it is such a large area of extreme cold, Antarctica plays an important role in global atmospheric circulation. In the tropics the Sun warms the air, causing it to rise and move toward the poles. When these air masses arrive over Antarctica, they cool, become heavier, and fall from the high interior of the continent toward the sea, making some Antarctic coasts the windiest places in the world. Winds on the Adélie Coast in the winter of 1912 to 1913 averaged 40 miles (64 kilometers) per hour 64 percent of the time, and gusts of nearly 200 miles (320 kilometers) per hour have been recorded.

Antarctica’s interior is one of the world’s major cold deserts. Precipitation (if melted) averages only 1 to 2 inches (2.5 to 5 centimeters) a year.

Plant and Animal Life

Antarctic hair grass (Deschampsia antarctica) is one of only two flowering plants that grow in…

Lomvi2

The severe climate has kept Antarctica nearly devoid of life. Plants are limited almost entirely to primitive types that are capable of surviving lengthy winter periods of total or near-total darkness during which photosynthesis cannot take place. The most common plants are lichens, which comprise about 350 species. Mosses and liverworts grow mostly in ice-free areas along the coast. Two species of flowering plants—a grass and an herb— are found on the peninsula and a few islands. More widespread than plants are numerous types of bacteria, algae, and fungi such as yeasts and molds.

The native land animals are limited to arthropods (such as insects), which become inactive during the coldest months. Nearly all the species are found only in Antarctica. These springtails, midges, mites, lice, and fleas live generally along the coast among plant colonies. Some species live as parasites on birds and seals.

The immense numbers of birds and seals that live in Antarctica are, properly speaking, sea animals. They spend most of their time in or over the water, where they get their food. These animals come ashore only to establish rookeries and breed.

Emperor penguins can be found around the entire coastline of Antarctica.

About 45 species of birds live south of the Antarctic Convergence. Two penguin species—the emperor and the Adélie—are distributed widely around the entire coastline. Gentoo and chinstrap penguins occupy Antarctic Peninsula coasts and some islands. Penguins are excellent swimmers and catch and eat their food—mostly krill (a shrimplike animal) and fishes—underwater.

The animal life of Antarctica includes Adélie penguins and leopard seals.

Stockbyte/Thinkstock

Sea mammals native to Antarctica include seals, porpoises, dolphins, and whales. Four species of seals breed almost exclusively in the Antarctic. They are the Weddell seal, which ranges as far south as the sea does and can dive as deep as 2,000 feet (600 meters) for nearly an hour; the crabeater seal, which spends most of its time around pack ice (sea ice); the leopard seal, which favors penguins as its food; and the Ross seal, rarely seen. Other Antarctic species include the fur seal and the huge elephant seal. Most populous is the crabeater, whose numbers are estimated to be in the millions. Among the whales of Antarctic waters are the killer whale, sperm whale, and rare bottle-nosed, or beaked, whale.

A marine biologist examines specimens hauled up from the depths of the Southern (Antarctic) Ocean,…

Contunico © ZDF Enterprises GmbH, Mainz

Fishes peculiar to the Antarctic include the Antarctic cod and the icefish. These and other Antarctic fish have developed blood that enables them to live in seawater as cold as 28 ° F (–2 °C).

Antarctic krill (Euphausia superba).

Matt Wilson/Jay Clark/NOAA NMFS AFSC

The most important single member of the Antarctic marine food chain is the krill. This crustacean looks like a small shrimp and exists in huge numbers; one vast swarm stretching several miles in length was observed from ships, and some biologists think the total population may be 5 billion tons or more. Krill eat small marine organisms called plankton and in turn are eaten in great numbers by squid, birds, seals, and whales. Economic Development

Antarctica is so far from world markets, and its environment is so hostile, that little economic development has taken place. Also, little is known about the amounts of natural resources that exist there. But, if world shortages of food and energy products become severe, Antarctica may be more intensely explored. Because no one country governs the land, however, exploitation of the continent’s resources would raise questions of ownership. In addition, economic development would be limited by the Antarctic Treaty of 1959, which preserved the continent for scientific research, as well as later international agreements designed to protect its resources.

The first people to make money by going to Antarctica were whalers and sealers. Seal hunters began catching Antarctic seals for their oil and fur in the late 1700s. Fur seals were reduced almost to extinction by the 1820s, at which point the sealers started hunting elephant seals. The hunting of elephant seals continued until 1964, when some 20 countries signed measures to protect the plants and animals of Antarctica. The Convention for the Conservation of Antarctic Seals, signed in 1972, established guidelines for any future sealing. It prohibits the taking of fur, elephant, and Ross seals and limits the annual catch of crabeater, leopard, and Weddell seals.

Whaling began in Antarctic waters in the 19th century. The industry enlarged greatly in the early 1900s, when steamships, harpoon guns, and shore processing stations (notably at South Georgia) were introduced. During the 1912–13 season 10,760 whales were caught. After that time nearly all the whales caught in the world were caught in Antarctic waters. In 1931, a peak year, 40,199 whales were caught in the Antarctic, while only 1,124 were caught in the rest of the world. So many whales were caught that their numbers declined, just as had those of the seals. The industry declined after 1960. In the 1980–81 season fewer than 6,000 whales were caught in the Antarctic; all were minke whales, a relatively small-sized species also called the lesser rorqual. In 1986 the International Whaling Commission banned commercial whaling, though Japan continues to take Antarctic whales in the name of scientific research.

The Soviet Union began commercial fishing on a large scale in 1967. Within a decade, intensive fishing led to severe declines in the numbers of Antarctic cod and other types of fish. Krill fishing began in the early 1970s and grew rapidly over the next decade. In response to these threats to the Antarctic ecosystem, multiple countries signed the Convention on the Conservation of Antarctic Marine Living Resources in 1982. This agreement—an addition to the Antarctic Treaty—set catch limits on krill, finfish, and other marine animals. After a period of decline, krill harvests increased again in the early 21st century as a source of food for the growing aquaculture (fish farming) industry.

Petroleum and other minerals have never been exploited in Antarctica. Minerals have been found in great variety on the continent but almost always in small amounts. Only two large mineral deposits have been found: iron ore in the Prince Charles Mountains and coal in the Transantarctic Mountains. However, it would cost too much to get these materials to market to make them economically attractive.

Large reserves of petroleum may exist in Antarctica, and oil has generally been considered to be the most likely prospect for exploitation. Little exploration has been done, however, and even if reserves were found, extraction would be difficult. The edge of the Antarctic continental shelf is 1,000 to 3,000 feet (300 to 900 meters) deep, much deeper than the world average continental shelf depth of about 600 feet (200 meters), and Antarctica’s icebergs would threaten drill rigs. Also, the environmental impact of spills would be greater in Antarctica

because low temperatures retard the growth of biological organisms that reduce crude oil to environmentally harmless components.

Even as these economic barriers discouraged mining in Antarctica, the Antarctic Treaty countries took an additional step to prevent the practice. In 1991 they signed a protocol to the treaty that prohibited the exploitation of mineral resources in Antarctica for 50 years. The protocol took effect in 1998, meaning that mining was banned until 2048.

Some people have devised ingenious schemes for towing Antarctic icebergs north to serve as a source of fresh water. As with the continent’s other potential resources, however, delivery costs would be too high to make these plans economically feasible.

Antarctica has abundant scenic resources, and it seems likely that they have greater potential for economic development than do mineral and biological resources. Commercial tourist visits to Antarctica began in the 1950s. Between 1958 and 1980 an estimated 16,600 passengers on 80 cruise ships visited places along the Antarctic Peninsula and in the Ross Sea. Tourism continued on a small scale until the 1990s, when the number of visitors began to multiply more quickly. In the early 21st century, the continent typically received a few tens of thousands of visitors each year. Most visitors come to the northern Antarctic Peninsula aboard cruise ships. A small but growing number of more adventurous tourists have ventured into or across the continental interior by ski, dog team, or private aircraft.

New technologies for landing large wheeled aircraft on inland ice sheets have opened possibilities for tourist facilities in many parts of Antarctica. Permanent accommodations for tourists ashore seem inevitable, especially in the Antarctic Peninsula. The flourishing tourist industry, however, has few controls under Antarctic Treaty regulations. Parties to the treaty are studying effects of tourism in order to provide regulations for ensuring protection of Antarctica’s highly sensitive ecosystem. Safeguarding penguin rookeries that particularly attract tourist photographers is of special concern. Problems created by the increasing tourism include sewage and waste disposal and the need for search and rescue facilities (a few tourist ships have gone aground or have been trapped in ice, requiring help). Political and International Relations

Because it has never had permanent human settlements, Antarctica has had an unusual political history. Seven countries have claimed pie-shaped sectors of territory centering on the South Pole. Three of the claimed sectors overlap on the Antarctic Peninsula. One sector is unclaimed. Most other countries do not recognize these claims. The United States policy, for example, is that the mere discovery of lands does not support a valid claim unless the discovery is followed by actual settlement. Also, like many other countries, the United States reserves all rights resulting from its explorations and discoveries.

This unsettled situation might have continued had it not been for a surge of scientific interest in Antarctica that developed in the mid-1950s. At that time scientists of 12 countries decided to make research in Antarctica the major portion of a large investigation, the International Geophysical Year. The 12 countries were Argentina, Australia, Belgium, Chile, France, Japan, New Zealand, Norway, South Africa, the Soviet Union, the United Kingdom, and the United States. When this program was completed in 1958, these countries decided to continue their research programs in Antarctica.

Much of the research had been achieved through international cooperation, and the 12 countries carried their new, friendly ties from science into politics. They met in Washington, D.C., in 1959 to sign the Antarctic Treaty. The treaty reserved the region for peaceful purposes, especially scientific research. It prohibits nuclear weapons

and disposal of radioactive waste on the continent, and it does not allow military activities there except to support science and other peaceful pursuits. The treaty does not recognize or dispute the territorial claims of any country, but it also does not allow any new claims to be made. It allows members to inspect each others’ installations, encourages the exchange of personnel, and requires each country to report to the others on its plans and results.

The Antarctic Treaty did not address all possible activities in Antarctica—for example, it included nothing about sharing the continent’s natural resources. It did, however, provide for regular meetings to further its objectives. At these meetings the original treaty countries, as well as others that later signed the agreement, have agreed on conservation plans and on responsible collection and sharing of resources. Scientific Research

Palmer Station is a research station that was built by the United States. It is located on Anvers…

Christopher Michel

The government of Norway owns a research station in Queen Maud Land, Antarctica. Scientists live and …

Islarsh

The International Geophysical Year (IGY) of 1957–58 began the modern era of scientific investigation of Antarctica. It established multiple year-round stations on the continent, including one at the geographic South Pole and one at the geomagnetic South Pole. Since then numerous Antarctic Treaty countries have carried out continuous scientific studies. A nonpolitical body called the Scientific Committee on Antarctic Research, or SCAR, coordinates the international scientific effort in Antarctica.

The scientific knowledge of Antarctica gained during and after IGY far outweighs that learned in the preceding millennia. This progress has been made possible by advances in technology, including jet aircraft, turbine- powered helicopters, ski-planes, and polar-orbiting satellites that automatically collect data across the continent and transmit it to a base collection station.

A computer-enhanced map, taken from satellite observations of ozone levels in the atmosphere over…

NASA

Researchers launch a balloon carrying an ozonesonde, an instrument that measures ozone in the…

NOAA

The research carried out in Antarctica encompass virtually all the physical sciences. Biologists, geologists, oceanographers, geophysicists, astronomers, glaciologists, and meteorologists conduct experiments there that cannot be duplicated anywhere else. Many important problems with relevance for the entire Earth are best studied in the polar region. One example is ozone depletion, the gradual thinning of Earth’s protective ozone layer in the upper atmosphere. In 1985 researchers reported that since 1977 the ozone over Antarctica had decreased rapidly in the springtime. Scientists found that this seasonal “ozone hole” resulted from the presence of man-made chemical compounds known as chlorofluorocarbons (CFCs), which were widely used in industry. This discovery led to strict regulations on the use of CFCs.

An image produced by NASA shows locations on Antarctica where temperatures increased between 1959…

GSFC Scientific Visualization Studio/NASA

A map shows the extent of collapse of the Larsen Ice Shelf in Antarctica. The Larsen A Ice Shelf…

Encyclopædia Britannica, Inc.

Another crucial research subject with worldwide implications is global warming. The effects of this gradual rise in Earth’s surface temperatures are most visible at the poles. West Antarctica is one of the fastest-warming places on Earth. The collapse of much of the Larsen Ice Shelf, part of the Antarctic Peninsula, between 1995 and 2002 was largely attributed to climate changes resulting from rising air temperatures. Continued melting of the glaciers and ice sheets of Antarctica could contribute to a dangerous rise in the global sea level. The impact of global warming was a main goal of the International Polar Year of 2007–08, an international research project focused on Antarctica and the Arctic.

History of Exploration

An engraving based on a sketch by Charles Wilkes shows his men on the Antarctic ice.

From Narrative of the United States Exploring Expedition by Charles Wilkes, U.S.N., Vol. II, 1849

The first expedition to come close to Antarctica took place from 1772 through 1775. The English navigator James Cook sailed around the continent and came within 100 miles (160 kilometers) of it. Land was seen about 1820, when separate British, American, and Russian expeditions all claimed first sightings. In 1821 the American sealer John Davis made the first recorded landing on Antarctica, at Hughes Bay, on the Antarctic Peninsula. In the Antarctic summer of 1839–40 a U.S. Navy expedition headed by Charles Wilkes mapped 1,500 miles (2,400 kilometers) along the coast of East Antarctica. The next summer James Clark Ross of Great Britain sailed into the Ross Sea, traveling as far south as a ship can go. The first recorded landing on mainland Antarctica was on Cape Adare in 1895, and the first group to spend a winter there did so from March 1898 to March 1899.

Beginning in the early 20th century, several explorers set out to reach the South Pole. Roald…

Encyclopædia Britannica, Inc.

Roald Amundsen, 1923.

UPI/Bettmann

The struggle inland and toward the geographic South Pole began with the first expedition by Robert F. Scott of Great Britain in 1901–04. A fellow Englishman, Ernest Shackleton, led an expedition that came within 112 miles (97 nautical miles, or 180 kilometers) of the pole in 1909. But the first person to reach the pole was Roald Amundsen of Norway on December 14, 1911. On another Antarctic expedition Scott arrived at the pole just a month later; he died on March 29, 1912, trying to return to the coast.

Richard E. Byrd.

These early expeditions relied on sail power, dog power, and human power for their transportation. The mechanical age arrived on November 16, 1928, when George Hubert Wilkins, leading an American expedition, made an airplane flight from Deception Island. On November 29, 1929, Richard E. Byrd of the United States flew a three-motor Ford plane over the South Pole. Byrd also explored parts of Antarctica by air and on the surface in 1933–35 and 1939–41 and commanded the largest single expedition to Antarctica yet attempted—the U.S. Navy’ s Operation High Jump in 1946–47. Thirteen ships, 25 airplanes, and thousands of men made surveys almost all the way around the continent.

Vivian Ernest Fuchs, center, with fellow expedition team members W. Stanley Moss (immediately left…

Shackleton made the first attempt at an overland crossing of Antarctica in 1914. His ship was caught and crushed, however, in ice in the Weddell Sea. The idea of an overland crossing lay dormant for several decades until it came to fruition during International Geophysical Year with the British Commonwealth Trans-Antarctic Expedition led by Vivian Ernest Fuchs. Using tracked vehicles and aided by aerial flights, the party left Shackleton Base on Filchner Ice Shelf on November 24, 1957, and by way of the South Pole reached the New Zealand Scott Base on Ross Island on March 2, 1958. In 1979–81 the continent was again crossed as part of the British Transglobe Expedition, which made the first polar circumnavigation of the world. In 1990 a six-man international expedition led by the American Will Steger completed a 221-day trek across Antarctica using dogsleds. At more than 3,700 miles (6,000 kilometers), it was the longest dogsled trek, as well as the first unmechanized passage through the South Pole. (See alsopolar exploration; world exploration at a glance.)

Guy G. GuthridgeEd. Additional Reading

DEWEY, JENNIFER. Antarctic Journal: Four Months at the Bottom of the World (HarperCollins, 2001).GOGERLY, LIZ.

Amundsen and Scott’s Race to the South Pole (Heinemann, 2007).HACKWELL, W.J. Desert of Ice (Scribner, 1991).

KALMAN, BOBBIE, AND REBECCA SJONGER. Explore Antarctica (Crabtree, 2007).MYERS, W.D. Antarctica: Journeys to the

South Pole (Scholastic, 2004).PRINGLE, L.P. Antarctica: The Last Unspoiled Continent (Simon & Schuster, 1992).

ROBERSON, DENNIS. Antarctica (Lucent, 2003).WOODS, MICHAEL. Science on Ice: Research in the Antarctic (Millbrook, 1995).

Citation (MLA style):

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coast

The area where the sea and land meet is called a coast. The coasts of the world measure about 312,000 kilometres (193,000 miles) in total. Coastal areas are also known as shores and seasides. They form unique habitats where a range of animals and plants survive in a challenging environment.

There are many different types of coast. They may be sandy, rocky, muddy or covered in shingle. Some have steep cliffs that are buffeted by waves, while others are broad stretches of land that alternate between being wet and dry as the tides go in and out. How Coasts Are Formed

Coasts have changed over millions of years. They are affected by geological events such as volcanic activity, ice ages and changes in sea levels. Two other factors that affect the shape and type of coast are erosion and deposition.

Erosion

Erosion is the wearing away of rocks or soil by the action of water, wind or ice. At the coastline, waves force pockets of air against rocks, which expand and explode, causing damage to the rocks over time. The continual force of waves against rocks and soil also wears them down, breaking them up into smaller and smaller fragments. Water that gets trapped in cracks and crevices can freeze in cold weather, causing more damage when it expands, forcing cracks to open wider. Plants, animals and humans can also cause coastal erosion.

Sea arches, like this one in Dorset, England, are formed by wave erosion.

Photos.com/Getty Images

Headlands and bays are features of coasts that are formed by erosion. Waves wear down different…

Encyclopædia Britannica, Inc./Patrick O'Neill Riley

Erosion at the coast can result in the formation of features such as sea caves, arches, bays and coves. One important effect of coastal erosion can be the loss of land and homes when cliffs fall into the sea.

Deposition

Deposition is the laying down of materials, such as rocks, stones, gravel, sand and mud. As rivers reach the shoreline they widen and lose much of their energy. When this happens, the load of materials they have been transporting is dropped to the bottom of the river bed or in the sea. Sandy beaches, estuaries, sand bars, spits, deltas and lagoons are the result of deposition. Animals and Plants

The living organisms that inhabit coasts form part of a special ecosystem. These animals and plants have to cope with extreme weather conditions of wind and rain, salty water, tides and waves. For this reason many coastal organisms do not live anywhere else.

Rocky shores are high-energy habitats where waves pummel the coast, making it difficult for animals to live there. However, when the tide goes out, rock pools provide sanctuaries for small crabs and soft-bodied animals such as sea anemones. Shelled animals, such as mussels and barnacles, attach themselves firmly to the rocks, and can withstand the biggest waves. Jellyfish and shells can sometimes be found washed up on the shore, particularly after a storm at sea.

Seaweed such as brown kelp and bladderwrack are common at coasts and sea lettuce forms a bright green, slimy carpet on smooth rocks. Multicoloured lichens cover exposed rocks above the waves.

On sandy beaches, lugworms live beneath the water: their holes and wormcasts are the only sign of their presence when the tide goes out. In drier zones, such as sand dunes and clifftops, spiky marram grass, sea lavender and pink thrift grow.

Sea birds often roost in coastal areas and the nests of terns and plovers can be found on rocky shores. Herring gulls, black-headed gulls, redshanks and common terns are amongst the many types of bird that visit coasts in search of food. Large birds, such as the peregrine falcon, build their nests on cliff faces. Fossils

The erosion of a coast can have unexpected benefits, revealing clues to the types of animals and plants that lived in the area millions of years ago. Fossils, or remains, of ammonites and other marine animals can be found on the Northumbrian and Dorset coasts of England, for example. The soft cliffs of East Anglia and the Isle of Wight have been eroded to reveal many ancient remains of animals that lived long ago, including dinosaurs, woolly mammoths and sharks. Coasts and People

Over thousands of years, coasts have proved to be good places to live, and human ancestors are known to have set up home by the sea. The water is full of life, such as fish and shellfish, so it provided a plentiful source of food. Caves and cliffs offered shelter from the weather and from predators such as wolves.

Coastal Settlements

Many coastal areas began to develop and change about 15,000 years ago as the Ice Age was drawing to an end. The ice melted, sea levels rose and people were able to move north. They began to inhabit caves, often near the shore. The United Kingdom’s oldest-known dwelling has been discovered by archaeologists at a cliff edge at Howick, in Northumberland. The people who lived there, around 9,600 years ago, collected flints from the coast to make their tools.

Travellers and Invaders

Living by the sea enabled people to trade with travellers from overseas. Coastal communities have since maintained strong links with other countries. They often have diverse cultures and foods, which reflect the wide variety of peoples that have visited their shores.

The Normans built Bamburgh Castle on the coast of Northumberland, England, so they could defend…

Photos.com/Jupiterimages

Unwelcome visitors, such as invaders, may also make their first appearance at coastal areas. For this reason, Britain’s coasts are peppered with castles and other military buildings which, through history, have provided a first line of defence against invasion. Dover Castle in south-east England was built on land that has been occupied as a defensive site since the Iron Age, at least 2,400 years ago. Bamburgh Castle in Northumberland was built by the Normans following their invasion in 1066. Pendennis Castle in Cornwall was built by Henry VIII to defend England against invasion by the Spanish and French. Changing Coastlines

Structures called groins, or groynes, protect coastlines from the power of the waves.

Coasts are continually changing. Deposition and erosion form and reform the land. Other changes are the result of the movement of plates that make up Earth’s crusts (seeplate tectonics). In the long term, sea levels rise and fall because of this movement. Scientists have also predicted that changes in climate caused by global warming will cause sea levels to rise. An increase in marine pollution is also affecting coasts and their delicate ecosystems.

Grasses help keep sand dunes in place.

In some places these changes can cause damage to buildings and can cause beaches to disappear. However, engineers have developed several different ways to protect coasts. Engineers can build structures to keep the waves from hitting the shore. They can also use the natural surroundings to help protect the coasts. They may replace sand that has been washed away, or they may restore sand dunes by planting grasses. The grasses help keep wind and water from blowing or washing the sand away.

Citation (MLA style):

"Coast." Britannica LaunchPacks: Landforms and Landscapes, Encyclopædia Britannica, 19 Feb. 2021. packs-ngl. eb.com.au. Accessed 6 Aug. 2021.

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desert

Any barren region that supports very little life may be called a desert. More commonly, however, the term desert is reserved for regions that are barren because they are arid, or dry. Arid deserts receive little precipitation and are characterized by specialized plants that tolerate drought conditions and salty soils. Occupying some 20 percent of the Earth’s surface, deserts are one of the planet’s main types of ecosystems. They may or may not be hot, and their land features range from windswept expanses of loose sand to rugged mountains, bare rock, and plateaus strewn with gravel and boulders.

Joshua trees and other yucca plants grow in the desert in Joshua Tree National Park in California.

Atacama Desert, Chile.

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Deserts are areas in which there is a shortage of moisture available for plants. There is no precise measure of how dry such an area must be to be called a desert. Characteristically, deserts receive an average of less than 10 inches (25 centimeters) of rain or other precipitation per year. Many deserts get less than half that amount of rain yearly, and some receive almost none. Regions with an average annual precipitation between some 10 and 16 inches (25 and 40 centimeters) are often called semideserts.

But rainfall is not the only factor that influences how much water is available to support plants. The distribution of the rainfall throughout the year, the humidity of the air, and the temperature and amount of sunshine all play a role. Some definitions of deserts focus on the imbalance between the amount of precipitation received and the amount of moisture that could be lost through evaporation and through plants’ leaves. In the Sonoran Desert, in the southwestern United States and Mexico, for example, a year’s potential evaporation—the amount of evaporation that would occur if water were always present—is some 100 inches (250 centimeters). This is about 20 times the actual annual rainfall.

Rainfall in deserts is not only scanty but also erratic. Most deserts have at least a few days of rain a year, but some may get no rain at all for several years or receive a year’s amount in one storm. For example, Iquique, in northern Chile, had no rain for a period of four years. The fifth year brought 0.6 inches (1.5 centimeters), making a five-year average of 0.12 inches (0.3 centimeter). At another time 2.5 inches (6.4 centimeters) fell in a single shower.

Most of the world's hot deserts lie between 20° and 35° north and south of the equator. The main…

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There are two main types of arid desert: hot and temperate. Most of the Earth’s deserts are found between 20° and 35° in both north and south latitudes, near the Tropic of Cancer and the Tropic of Capricorn, respectively. Except for a couple of coastal deserts kept cool by ocean currents, these deserts are hot. They occupy subtropical regions that straddle a wet, tropical region around the equator. Because of the predominant air- circulation patterns, the air that descends into the subtropical regions has already rained out most of its moisture over the tropical lands. The air is also heated as it descends, which further prevents rain.

Temperate deserts are found farther from the equator, in the middle latitudes. They occur mainly in Central Asia, with smaller areas in western North America, southeastern South America, and southern Australia. These deserts are generally separated from the coast by mountains or by great distance. Air picks up moisture from the ocean, but by the time it reaches these regions, it has lost much of its moisture over either the mountains or the land nearer the coast.

Ice cap and tundra regions around the poles are sometimes called cold deserts. They have little precipitation, but the dearth of vegetation is caused chiefly by the cold.

Temperatures range widely in deserts. In hot deserts, daytime air temperatures above 100° F (38° C) occur regularly in summer. Al Aziziyah, Libya, holds the record for the hottest temperature with a high of 136° F (57.8° C), while Death Valley, Calif., comes close with 134° F (56.7° C). Winters are cold in temperate deserts, located far from the equator. The Gobi, in Central Asia, for example, has an average low temperature of −40° F (−40° C) in January and an average high of 113° F (45° C) in July.

The temperature drops sharply in the desert night. Dry air, cloudless skies, and bare, dry earth furnish ideal conditions for the cooling of air after sunset. A 24-hour range of 25 to 45 Fahrenheit degrees (14 to 25 Celsius degrees) is common, and it may exceed 60 to 70 Fahrenheit degrees (33 to 39 Celsius degrees). Land Forms

People get water at a well in the Thar (Great Indian) Desert, in western Rajasthan, India.

Sagebrush blooms in the Chisos Mountains, in Big Bend National Park, in southwestern Texas. The park …

Desert areas differ greatly in their surface features, which range from mountains to plateaus to plains. The ground may be bare rock or be covered with sand, scattered boulders, or a “desert pavement” of coarse gravel and stones. Although sand dunes are spectacular features of deserts, they are not as common as generally believed. In the deserts of the southwestern United States, for example, dunes occupy less than 1 percent of the surface. In the most sandy of all deserts, the Arabian, dunes occupy only about 30 percent of the total area. If sand accumulations on plains are extensive and appear as a “sand sea,” they are called ergs.

A more common type of desert consists of rugged mountains separated by basins called bolsons. The mountains receive most of the rains in downpours. As the water rushes down the steep slopes it cuts deep gullies and carries rock fragments, gravel, and sand to the bolson. These materials are freed from the water when it slows

or evaporates, and they are deposited as cones or in fans of sediment called alluvial fans. The rugged forms produced in this way, such as the terrain in Death Valley, are termed badlands.

Sometimes floodwaters make a temporary shallow lake in the basin. The temporary lakes that form in basins with no outlet are called playa lakes. Typically the water soon evaporates into the air or filtrates into the ground, leaving behind sediments of clay, silt, and sometimes salt. The flat-bottomed depression that is formed by the water is called a playa. In narrow basins, alluvial fans and badlands may extend to the edge of the playa. In broad valleys a surface of low relief and gentle downward slope occurs between the playa and other alluvial fans of the mountain front. Such a surface is called a desert flat or llano.

Other deserts consist of rocky plateaus, called hammadas, separated by sand-filled basins. Here differences in altitude are usually slight. Many hammadas are broad, almost flat, dome-shaped areas. Where streams or wind wear away the weaker rocks, strong rock formations stand out boldly as mesas or cuestas. Pinnacles, needles, and arches carved in colored rocks lend fantastic beauty to the deserts of the American Southwest. Gullies are cut deep into the hammadas by the wearing force of the torrents. Gullies are known as wadis in Arabia and arroyos in the Southwest. Plants and Animals

Plants in the deserts of Arizona have varying strategies to survive the dry conditions.

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Few parts of the desert are entirely barren. Where water seeps toward the surface, a great variety of plants spring up. After a rain low shrubs and grasses come to life. At blooming time, the plants are fragrant and bright with color. They grow quite far apart, instead of providing complete ground cover. Trees and large shrubs can be found in the desert, but they are not prominent in the driest regions.

Learn about the saguaro cactus, a plant unique to the Sonoran Desert, as found in Saguaro National…

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Desert plants differ in the ways they are adapted to arid places. Some plants sprout when the rain falls, bloom quickly, ripen their seed in a few days, then wither and die. Other plants survive periods of water shortage by drying up and becoming physiologically inactive. When more water becomes available they swell up and resume activity. Some desert plants depend upon underground water and have long root systems, while others are able to absorb dew. Various adaptations of the leaves, such as smaller surface areas, help prevent the loss of moisture. In most species of cactus, for example, leaves are either absent or very small. Cacti and other succulent plants also store water in their thick, fleshy tissues to help them survive long dry periods. (See also sagebrush.)

Animals live in all but the most barren stretches. The camel is the most useful domestic desert animal. Its physical structure permits it to travel far without water. Various wild mammals, birds, and reptiles of arid regions must get all their moisture from their food. In times of drought, many desert animals remain inactive for long periods. Others hide from the sun during the hottest daytime hours and come out at night to feed. More than half of desert animals live at least part of the time underground, where it is cooler and more humid. Another strategy is migration: many birds and other desert animals survive by regularly moving to areas that have recently received rain. People and Deserts

Deserts are much less densely populated than other land areas. People can live and grow crops in the desert only at places where they can get water, called oases. In some spots ordinary shallow wells reach the water table, or the upper boundary of underground water, but usually groundwater lies at greater depths in deserts than in humid lands. In alluvial fans the water sinks deep into the porous material, but it may be reached by a well at the tip of the fan.

In wadis, ordinary wells can usually tap a supply of good water. Oasis settlements therefore are most often found where wadis are numerous. Ergs into which many wadis drain may have a water supply. Desert shrubs in the hollows between the dunes signal its presence. Deep artesian wells may be bored where the rock structure holds water under pressure. In some oases an artesian spring flows through a crack in the rock.

Streams that rise in rainy regions outside deserts bring the most generous supply of water for irrigation. All the large deserts except those of Australia are crossed by these so-called exotic rivers. The largest and best known of them are the Nile in Egypt, the Tigris and Euphrates in Iraq, the Indus in Pakistan, and the Colorado in the United States.

Desert soils are usually productive when given water. They are coarse textured and highly mineralized. Most widely cultivated are the water-transported soils of floodplains and alluvial fans. Land is precious in oases, so it is intensively cultivated. In North African and Asian oases, the chief food crops are dates, figs, wheat, barley, rice, and beans. Oasis farmers also raise such crops as cotton and sugarcane. In the United States irrigated lands are mainly used for citrus fruits, dates, winter vegetables, and cotton.

The proper development of critical water resources has focused on improving surface-water management techniques, improving control and storage of surface runoff, reducing loss from shallow aquifers, and desalting brackish waters. The buildup of salts in the soil has become a serious problem that is being studied in several nations. The introduction of cultivated plant species with greater salt tolerance, as has been done in Israel, seems to be a promising alternative to abandoning arid land.

Humans have changed many desert environments. Irrigated lands have been extended by giant river-control systems. Oases once reached only by camel now have airports and gas stations for motor vehicles. Settlements have sprung up in deserts to obtain such valuable minerals as the petroleum of Saudi Arabia, Iraq, and Iran and the copper and other metals of arid North and South America. Typical desert minerals are soluble salts left behind by evaporation. Sodium nitrate, the most valuable, comes from the north Chile desert.

The mismanagement or overuse of arid and semiarid lands can cause desertification, or the spread of desert environments. Excessive cultivation of the land, clearing away the vegetation, or exhausting the water supply can rob arid or semiarid land of its ability to sustain life. Factors such as long-term climate change or severe drought can also cause desertification.

Charles William Finkl, Jr.Ed.

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Echo Caves

The Echo Caves are among the oldest caves in the world. These limestone caves are in the Molapong Valley in the South African province of Limpopo, about 6 miles (10 kilometers) west of Motlatse Canyon. The name derives from the echoes that are heard when rock formations within the caves are struck. The echoes can be heard outside the caves.

The cave system is about 25 miles (40 kilometers) long, but its full extent is unknown. One of the largest rooms in the system is about 328 feet (100 meters) long and 190 feet (60 meters) high. The Madonna and Crystal Palace chambers are some of the latest discoveries. Visitors can go on guided tours.

The caves have many impressive rock formations, including stalagmites and stalactites. A stalagmite is cone- shaped and rises up from the cave floor. A stalactite is a cone that hangs from the ceiling.

People lived in the caves in prehistoric times. Cave dwellers may have used the rock formations as drums to warn each other when danger was near. Tools and other evidence of these early people are exhibited in a museum near the caves. There is also rock art in the caves that was made by the San people hundreds of years ago.

The caves were unknown to European settlers in the region until 1923, when the owner of a farm called Klipfonteinhoek found them. When his cattle disappeared, the farmer wanted to find out what had happened to them. He discovered that the cattle had been going into the Echo Caves.

The caves were not open to the public until 1960, after the completion of the Abel Erasmus Pass and the J.G. Strijdom Tunnel through the Drakensberg range. The caves were later declared a South African national monument.

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Grand Canyon

One of the most spectacular sights in the United States – or anywhere in the world – is the Grand Canyon. The canyon was cut through many layers of rock by the waters of the Colorado River. At the canyon’s deepest point, the river now flows more than 1.6 kilometres (1 mile) beneath the level of the rim. The canyon runs for 446 kilometres (277 miles) through the high plateaus of north-western Arizona, ranging from about 0.2 to 29 kilometres (0.1 to 18 miles) wide.

Mather Point overlooks a spectacular view on the south rim of the Grand Canyon, in Grand Canyon…

E. Cooper/H. Armstrong Roberts

The Grand Canyon is located in north-western Arizona.

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The rocks of the Grand Canyon are millions of years old.

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The oldest rocks that the canyon passes through are billions of years old. The canyon itself is much newer. It was formed in the last 5 to 6 million years. The sandy waters of the river wore down the soft rocks on its banks, creating a fantastically rugged landscape of peaks and ravines. Much of the history of Earth’s crust can be traced in the exposed layers of multicoloured rock.

Willow trees and cottonwoods grow at the bottom of the canyon where there is plenty of water. There are magnificent forests of pine, fir, spruce and aspen on the north rim of the canyon. On the drier south rim, pines and junipers grow. Much of the vegetation in the inner canyon is that which is commonly found in deserts, including cacti and drought-resistant shrubs.

The canyon is rich in wildlife, including coyotes, foxes, deer, badgers, pumas, bobcats, rabbits and chipmunks. The Kaibab squirrel lives only among the ponderosa pine trees of the north rim. Many kinds of birds, including peregrine falcons and great horned owls, make their home in the canyon. There is a wide variety of snakes and lizards as well as insects, spiders, scorpions and centipedes.

Human Presence

Native Americans have lived in the Grand Canyon region for many centuries. Evidence of the canyon’s prehistoric residents includes ruins of Anasazi cliff dwellings and artefacts such as pottery. Several Native American groups, including the Havasupai and the Hualapai, now live on nearby reservations. In 1540 troops of the Spanish explorer Francisco Coronado became the first non–Native Americans to reach the canyon.

Riding mules through the Grand Canyon is a very popular activity.

The Grand Canyon National Park was declared a UNESCO World Heritage site in 1979.

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Grand Canyon National Park was established in 1919. It was greatly enlarged in 1975, and it now covers 493,076 hectares (1,218,375 acres). In 1979 the canyon was named a World Heritage site by the United Nations Educational, Scientific and Cultural Organization (UNESCO). The park attracts millions of visitors each year. Mule- pack trips and river rafting are popular ways of viewing and experiencing the beauty of the vast canyon. A paved road and a trail connect the north and south rims.

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Great Victoria Desert

An immense dry area known as the Great Victoria Desert stretches across southern Australia. It lies in the states of Western Australia and South Australia, between the Gibson Desert on the north and the Nullarbor Plain on the south. The Great Victoria Desert extends eastward from Kalgoorlie almost to the Stuart Range. It covers an area of about 250,000 square miles (647,000 square kilometers). Most of the desert consists of a vast expanse of sand dunes, though in some places a layer of tightly packed pebbles covers the ground.

Great Victoria Desert, Australia.

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Spinifex grass grows in the Great Victoria Desert of southern Australia.

The Great Victoria Desert receives only about 6 to 10 inches (15 to 25 centimeters) of rain each year. The desert has very hot summers and cooler winters, when nighttime temperatures may drop below freezing.

Grass of the genus Triodia (Spinifex) grows in parts of the desert, and there are also scattered acacia trees and shrubs. Wildlife includes reptiles such as skinks, geckos, monitor lizards, and copperhead snakes as well as mice, dingoes, and foxes.

The Great Victoria Desert was named by the Australian explorer Ernest Giles, who led a party across it from east to west in 1875. Few people live in the desert. Some Australian Aboriginal people live in the eastern regions. The

Australian government uses parts of the Great Victoria Desert to test weapons. There are several national parks and nature reserves in the area, including the Great Victoria Desert Nature Reserve and Nullarbor National Park.

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Huang He (Yellow River)

The main river of northern China, the Huang He (or Hwang Ho) is the second longest river in the country, after the Yangtze. It rises on the Plateau of Tibet and flows generally eastward, emptying into the Yellow Sea. Chinese historians routinely refer to the Huang He as the cradle of Chinese civilization. The river, its tributaries, and its valley have played an integral part in the history of China for more than 3,000 years. Along the middle and lower reaches of the system, Chinese civilization and agriculture first developed, and the earliest capitals of the dynastic era, Anyang and Luoyang, were located there. Control of the river and its drainage area provided the great surplus of grain required for China’s military and political expansion beginning in the Qin Dynasty (221–

207 BC).

The Huang He (Yellow River) is the main river of northern China. It flows eastward from the Plateau…

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Aerial footage shows the Huang He (Yellow River) at Linfen, Shanxi province, and of the Hukou Falls, …

The Huang He (Yellow River) flows through land in the Hui Autonomous Region of Ningxia, in…

Huang He means “Yellow River.” The river gets its color and its name from the extremely high volume of yellow- brown windblown silt, or loess, that enters the river in its middle reaches as it cuts through the Loess Plateau. The high silt load makes the lower reaches of the river prone to disastrous flooding. For this reason, the Huang He has been known as “China’s sorrow” or the “river of tears.” Flood-control and irrigation works have been built along the river for centuries, and dams, begun in the mid-1950s, also produce hydroelectricity.

The Huang He flows through the countryside in Qinghai province, China.

One of the world’s longest rivers, the Huang He is 3,395 miles (5,464 kilometers) long. It drains an area of some 290,000 square miles (750,000 square kilometers). The course of the river can be divided into two distinct sections—the mountainous upper reaches and the plains portion, which is often subdivided into the middle and lower basins. The headwaters of the river lie in western China, in the Kunlun Mountains of Qinghai province.

The middle basin includes the course of the river through the Ordos Desert and the Loess Plateau. It forms a great bend, flowing first to the northeast, then to the east and south. In this section the Fen River and the Wei River, the most important tributary, join the Huang He. The river then turns sharply east.

Junks sail on the silt-laden Huang He (Yellow River) near Zhengzhou in Henan province, China.

Tim Megarry/Robert Harding Picture Library

The lower basin, beginning in northern Henan province, encompasses the great North China Plain, which extends to the sea, interrupted only by the hills of Shandong province. The plain has been farmed and densely populated for thousands of years. The marshy delta begins about 50 miles (80 kilometers) from the river’s mouth on the Bo Hai, a gulf of the Yellow Sea. Over the centuries, the mouth of the river has moved many times, to points as much as 500 miles (800 kilometers) to the north and south of the Shandong peninsula.

Central to all problems of the river’s shifting course, flooding, and water management is its great load of silt. The river has the highest silt load of any major river in the world, with every cubic foot of water carrying more than 2 pounds (0.9 kilogram) of silt. Some of the silt settles to the bottom and gradually builds up the riverbed. In some places the riverbed is far higher than the surrounding plains, which can cause the river to flood or to shift its course to lower land.

The system of levees that now lines virtually all of the lower reaches of the river was begun prior to the 6th

century BC. Levees are mounds or ridges built along the edges of a river to prevent flooding. Unfortunately, on the Huang He the long-term effect is only to delay flooding. By constraining the channel, over time the levees cause silt deposits to raise the riverbed more and more. When a levee is breached or overtopped, the floodwater can inundate thousands of square miles of low-lying farmland and bring ruin on the inhabitants. In China’s history extensive flooding has occurred countless times, and several of the most terrible floods, with their ensuing famines, have been responsible for the deaths of more than a million persons at a time. After the southern levee of the river failed in Hunan province in 1887, more than two million people died from drowning, starvation, or the epidemics that followed. Modern flood-control programs on the river include not only improved levees but also dams and projects to reduce erosion on the Loess Plateau—and thus the amount of silt the river picks up.

The high silt load of the Huang He has also limited the utility of the water for navigation, power generation, urban consumption, and industry. In the early 21st century a massive construction project began diverting water from the Yangtze to the North China Plain. This extremely expensive and ambitious project was developed because the water available to this growing urban-industrial region from the Huang He system had fallen far short of demand.

Gregory VeeckEd.

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Indigenous Australians and the Environment

Indigenous Australians—the Aboriginal and Torres Strait Islander peoples—have an intimate connection to the land, waters, and living things. Their values, identity, spirituality, and lifestyles have all been strongly influenced by the environment in which they live. This relationship with the natural world comes from their belief that all the elements of the universe, including humans, plants, animals, landforms, and waterways as well as the Sun, Moon, and stars, were all created by ancestral (spirit) beings. After the creation of the world, these spirits became part of the landscape, and they live on in mountains, rivers, and other natural features today.

Because the environment is essential to their well-being, Indigenous Australians have a deep respect for nature. They have always felt a responsibility to care for and protect the land and waters. Over tens of thousands of years of living close to nature, they learned how to use the environment to meet their needs while also ensuring that natural resources would continue to be available for future generations. Some of their methods, such as firestick farming, continue to be models for sustainable environmental practices today. Caring for Country

Within traditional Aboriginal and Torres Strait Islander societies, each clan has a defined area of land, or Country, to which they are connected or belong. Indigenous peoples identify themselves through their specific territory. Each clan has built a unique body of knowledge based on its Country that is handed down through generations by the elders. Clan members learn where to find sources of water and how to identify edible plants. They also learn the effects of seasons on plants and animals as well as how to track animals for hunting.

Knowledge about Country also includes practices for managing the land and its resources, which are known as “caring for Country.” Although these practices vary according to location, Indigenous Australians share the belief that conserving resources is essential. Traditionally, Indigenous groups would stay in an area only for a certain period of time to prevent excessive hunting, fishing, or harvesting, thereby maintaining a steady food supply. They also moved from place to place to adapt to changes of the seasons, which affected the availability of food sources. Natural Resources and Their Uses

Traditionally, Aboriginal and Torres Strait Islander peoples depended on natural resources for nearly all of their everyday needs. Plants, animals, and waterways provided food, medicine, shelter, and tools and weapons.

Food

An Australian Aboriginal woman sorts fruit. Her ancestors were traditional hunters and gatherers.…

Traditional food from Australia's Outback is called “bush food.”

Courtesy of AIATSIS (collection item no. 000125299)

Traditional Indigenous Australian peoples were hunters and gatherers. Men hunted mainly for larger animals, such as kangaroos, emus, birds, reptiles, and fish. Women and children hunted small animals and collected fruits, honey, insects, eggs, and plants. They took only the animals and plants that were needed, and nothing was wasted. Traditional Indigenous food was rich in nutrients and varied according to the seasons and location.

Medicine

Aboriginal and Torres Strait Islander peoples used traditional medicines to treat such ailments as burns, snake bites, jellyfish stings, headaches, and eye infections. These treatments were referred to as “bush” medicine because all the ingredients used to make the ointments or remedies were gathered from the natural resources in the bush. Each clan used different medicines, depending on which plants and animals were available in their environment and in different seasons. Remedies included the use of wild herbs, bark and sap from trees, soil, animal products, and leaves. Knowledge of which plants or products treated particular conditions and how to prepare those remedies was part of the body of knowledge passed down through the oral tradition.

Shelter

Indigenous peoples traditionally lived in simple shelters made of materials that were available in a clan’s Country. The types of shelters used depended on many factors, including climate and the size and needs of a family. Typically, a shelter was made from a frame of branches and covered with leafy branches or sheets of bark. In areas where the environment was rich with resources, more complex and permanent shelters were built because a family group would live off the local resources for longer. These dwellings were built with the strongest materials available, such as hardwood, bark, and woven strings and twine.

Tools and Weapons

Axe grooves can be seen in a rock in Kangaroo Valley, New South Wales, Australia. Aboriginal people…

Courtesy of AIATSIS; creator, Josephine Flood (collection item no. 15262)

Some Australian Aboriginal peoples made and traveled in bark canoes.

Courtesy of AIATSIS; creator Jon C. Altman (collection item no. N03187_23)

Traditional Indigenous societies also used natural materials to make a variety of tools and weapons. All clans had implements such as knives; spears for hunting, fishing, and fighting; boomerangs for hunting, warfare, and ceremonies; bowls for gathering, eating, and drinking; and clubs for ceremonies, fighting, and digging. The

materials used to make tools and weapons depended on the resources available in each environment. In areas near the coast, for example, fishbone was used to make tips on spears, but in desert areas stone tips were used.

An Australian Aboriginal warrior prepares to throw a boomerang.

©Rafael Ben-Ari/Fototlia

Australian Aboriginal men demonstrate combat with waddies (traditional war clubs) in Western…

Courtesy of AIATSIS; creator, Commander H.T. Bennett D.S.Q. (collection no. D00029609)

Wooden tools and weapons, such as spears, boomerangs, and clubs, were made from local hardwood trees. In central Australia wood from wattle (or acacia) trees was a common material. In southeast Australia she-oak was used. The wood used to make tools and weapons also varied according to the purpose of the implement. For example, people in desert areas used heavy wood to make boomerangs for hunting large animals, such as kangaroos. People who lived along the coasts made lighter boomerangs for duck hunting. Spears made for fishing were also made from lighter materials. Firestick Farming

Australian Aboriginal people burn a patch of land to flush out kangaroos for hunting, in a painting…

Joseph Lycett, National Library of Australia, nla.obj-138501179

Two Australian Aboriginal men demonstrate how to make a fire.

Aboriginal peoples have traditionally used fire as a way to manage the land. In the practice called firestick farming, they strategically burned parts of the bush. Controlled burning served several purposes. It reduced the risk of destructive bushfires by clearing vegetation that could have served as fuel. It also increased the amount and diversity of food available by encouraging the growth of different kinds of plants in different areas throughout the year. The heat from fire triggered the germination of seeds, leading to the growth of food plants, and the ash served as a fertilizer to encourage growth. The abundance of fresh vegetation attracted animals that Aboriginal peoples hunted, such as kangaroos, wallabies, and bilbies. Thinning the vegetation also flushed these animals out into the open to make hunting easier.

One example of the benefits of firestick farming was in desert areas that were usually covered with spinifex grass. Aboriginal peoples burned the spinifex, clearing the land for growth of edible plants. Among them were wild tomatoes and wild bananas, which were staple foods for people of the desert. Cultural and Economic Value of Water

Kakadu National Park in the Northern Territory of Australia features a wealth of Aboriginal rock…

Indigenous Australians, like all people, need water to survive. For Aboriginal and Torres Strait Islander peoples, however, water is more than a physical resource. It has always held great cultural, spiritual, and economic value for Indigenous communities.

Australia is the driest inhabited continent on Earth. Half of the continent receives less than 12 inches (30 centimeters) of rainfall per year, and about three-quarters of the land is classified as arid or semiarid. Aboriginal peoples had to learn how to live in remote areas where water was often in very short supply. Over many

generations they developed a deep understanding of the availability, movement, and properties of water—where to find it, how to conserve it, and how to use it to acquire food.

The Murray River flows through Victoria on its way to South Australia and the Indian Ocean.

Nathan Hurst

A fish-trapping fence in the Northern Territory suggests that early Australian Aboriginal peoples…

Courtesy of AIATSIS; creator, Jon C. Altman (collection no. N03211_35)

Many Aboriginal groups settled near the coast or along rivers or lakes. The Murray River, the longest river in Australia, has supported Aboriginal communities for many thousands of years. Traditionally, fish, crayfish, and mussels were caught using nets and spears made from reeds, rushes, and branches found around the river and creeks. Waterbirds such as ducks, pelicans, and black swans were also trapped in nets and cooked over a fire. Plants and trees along the river provided food as well as materials for making tools and medicine. Canoes were built from the bark of the river red gum, the most common eucalyptus tree along the Murray. Aboriginal peoples used the canoes for fishing, setting out nets, and crossing the creeks when they flooded at certain times of the year.

The Great Barrier Reef lies off the northeastern coast of Australia.

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Water has always been vitally important to Torres Strait Islander culture. Traditionally, Torres Strait Islander peoples relied on the sea for survival. They got much of their food by fishing, collecting shellfish, and hunting sea animals such as turtles and dugongs in the surrounding waters of the Torres Strait, which lies between the Australian mainland at Cape York and Papua New Guinea. They also collected sea resources from the Great Barrier Reef, which begins in the Torres Strait and runs south off the Queensland coastline. Today, fishing remains an important part of the economy, and seafood is still a staple of the diet. Another key economic activity of Torres Strait Islander peoples was sea-based trade. They exchanged pearl shells, turtle shells, feathers, and other items with each other and mainland Aboriginal communities as well as peoples of Papua New Guinea. Their long voyages along the Great Barrier Reef and to neighboring islands were made possible by sturdy canoes they fitted with floats called outriggers.

A rock painting represents the Rainbow Serpent. In Australian Aboriginal stories of the Dreaming,…

The significance of water to Indigenous Australians is reflected in their spiritual beliefs. There are many stories about water in the Dreaming, or Dreamtime, the body of Aboriginal beliefs about the formation of the world. One well-known spirit being that is strongly linked with rain and rivers in Aboriginal beliefs is the Rainbow Serpent. Although stories of the Rainbow Serpent vary from one region to another, all of them depict the snake as the creator of watercourses and the source of all life. The most common story tells that the world was a flat, cold, empty landscape during the Dreaming. The Rainbow Serpent pushed up from beneath the ground and moved across the land creating mountains, valleys, and hills and spilling out water, forming rivers, lakes, and water holes. When a rainbow is seen, it is believed to be the Rainbow Serpent traveling from one water hole to

another. Among the Torres Strait Islander peoples, spirituality centers on the stories of Tagai, a great fisherman and spirit being who is believed to have created the world. The Tagai stories depict the Torres Strait Islander peoples’ intimate connection to the sea. Spiritual Significance of Landforms

The creation stories of Indigenous Australians do not only describe how spirit beings created the world long ago. They also explain that the spirit beings live on in rocks, trees, mountains, rivers, lakes, and reefs. Some of these natural features have particular spiritual significance for Indigenous Australians and are considered sacred sites. These sites are scattered across the continent. Some are known only to local Aboriginal peoples, but others are part of Australia’s most prominent landforms. The Indigenous views of three famous places—Uluru/Ayers Rock, the Great Barrier Reef, and the Snowy Mountains—show the deep spiritual connections tying Indigenous Australians to the land.

The rock formation known as Uluru/Ayers Rock is important to many Aboriginal peoples of the region.…

Uluru/Ayers Rock is located in the Northern Territory of Australia.

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Uluru/Ayers Rock is a giant sandstone rock that rises 1,142 feet (348 meters) above the desert landscape of southwestern Northern Territory in central Australia. It is a sacred site for the Aboriginal people of the region, the Anangu. The Anangu believe the rock was created by their ancestors during the Dreaming on what had until then been a flat, featureless plain. Dreaming stories tell of the formation of the many features of the rock, including caves, cliffs, boulders, and cracks that the Anangu attribute to the activities of their ancestors. Carvings and paintings on the walls of caves at the base of the rock depict the creation of sacred features.

The traditional Aboriginal name for the rock is Uluru. The first European to see the rock, in 1873, called it Ayers Rock. In 1985 the Australian government recognized the importance of the rock to the Anangu by giving them official ownership. The rock’s name was officially changed to Ayers Rock/Uluru in 1993 and to Uluru/Ayers Rock in 2002. The rock is part of Uluru–Kata Tjuta National Park, which was named a UNESCO World Heritage site in 1987.

The Great Barrier Reef and its sea life hold special significance for Indigenous Australians of the…

The Great Barrier Reef is another World Heritage site of great importance to Indigenous Australians. More than 70 Aboriginal and Torres Strait Islander groups have a strong spiritual and cultural connection with this natural phenomenon off the Queensland coast. They are considered the traditional owners of the reef. Aboriginal peoples have Dreaming stories that tell how their ancestors lived on land in the Great Barrier Reef region before a rise in sea level flooded the area more than 10,000 years ago. The flooding created the islands of the region. Scientists attribute the sea level rise to the melting of glaciers at the end of the latest Ice Age. Dreaming stories, however, describe how ancestral spirits created the islands. The Aboriginal Dingaal people of northern Queensland, for example, have a story relating how the Lizard Island group was formed in the shape of a stingray, with the main island (Jiigurru) as the body and the other islands as the tail. The Dingaal consider Lizard Island to be a sacred site and have performed male initiation ceremonies there.

Creation stories also depict sea animals that have special significance for Indigenous peoples. For example, a story from Murray Island in the Torres Strait tells how Nageg and Geigi, a mother and son, became the fish now known as the triggerfish and the great trevally. Many Indigenous groups in the reef region have adopted a marine animal, such as a shark, turtle, crocodile, or sea bird, as a family or clan emblem. These animals, known as totems, play a special role in the groups’ songs and dances.

The Snowy Mountains, the highest mountain range in the Australian Alps, are located in southeastern New South Wales and eastern Victoria. The traditional owners of most of the Snowy Mountains region are the Aboriginal Ngarigo people. Neighboring Aboriginal groups include the Wiradjuri, Walgalu, and Southern Ngunnawal. All of these peoples have strong cultural and spiritual connections to the mountains.

The archaeological and sacred sites of the region include stone arrangements, burial sites, and rock shelters. Stone arrangements, typically found at the top of the highest mountains, were used for initiation ceremonies. Carved trees mark the burial sites of prominent clan members. Rock shelters show evidence of occupation from more than 20,000 years ago. The oldest known Aboriginal site in the area is Birrigai Rock Shelter in the Tidbinbilla Nature Reserve, on the northern fringes of the Alps. Tidbinbilla is part of the traditional Country of the Ngunnawal. Its name comes from a Ngunnawal word meaning “where boys become men,” reflecting the

initiation ceremonies performed on the mountaintops. The shelter is still highly valued by the Ngunnawal and other Aboriginal peoples today.

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mountain

A mountain is a landform that rises prominently above its surroundings. It is generally distinguished by steep slopes, a relatively confined summit, and considerable height. The term mountain has topographic and geologic meanings. It generally refers to rises over 2,000 feet (610 meters).

Young mountains have steep slopes and high, pointed peaks. Old mountains in contrast have rounded…

The Black Hills of western South Dakota and northeastern Wyoming consist mostly of dome mountains.…

Compared to a hill, a mountain is defined by its greater height and volume. A plateau is distinguished by its flat surface and a mountain by its greatly irregular surface. Most mountains are peaked, but many have flat tops.

Mount Everest, which borders China and India, is the highest peak in the world, towering 29,032 feet (8,849 meters) above sea level.

Altimetry is the measurement of altitude, or elevation above sea level. Mountain altitudes can be measured by an aneroid barometer designed to register changes in atmospheric pressure accompanying changes in altitude, by radar altimetry, or by the traditional triangulation survey of points of known altitudes. Modern satellites make it possible to determine the elevation of any remote peak on Earth..

Subsea mountains, usually volcanic cones, are commonly associated with midoceanic ridges or hot spots in the Earth. The massive volcanoMauna Loa, on the island of Hawaii, is one of the largest mountains in the world. It rises 6 miles (10 kilometers) above the sea floor—2.6 miles (4.2 kilometers) of which are above sea level—and has a basal diameter of about 60 miles (97 kilometers).

Mountains have played a major role in human history, forming geopolitical boundaries between countries and natural barriers to migration and transportation. They also have formed refuge areas for distinctive mountain cultures and economies such as those that have flourished in the Himalayan nations of Tibet and Nepal. Potential waterpower and mineral deposits are commonly found in mountains but are frequently expensive to develop.

Mountains such as those along coastal regions of Washington, Oregon, and California in the United States are often associated with special weather conditions. Here moist air masses move inland from the Pacific and are cooled by forced ascent over these mountains, producing heavy rainfalls on the windward slopes. This is called the orographic effect. The eastward mountain slopes are in a rain shadow where rainfall is much less. The foehn and chinook are warm, dry winds that move down mountain slopes, often melting snow and causing avalanches or parching a landscape. Types of Mountains

Of the several kinds of mountains that exist, most may be defined in terms of geologic structure. Although most mountain chains share certain common features, mountains can be broadly grouped into five specific types.

Dome Mountains

Dome mountains are formed where a region of flat-lying sedimentary rocks is warped or bowed upward making a structural dome. Their topography is characterized by a relatively flat, dissected surface sloping gradually toward the surrounding lowlands, or basins. The diameters of the bases of dome mountains range up to hundreds of kilometers. These mountains may also result from the erosion of a structural dome. Typical examples of domed mountains include the Black Hills of South Dakota and the Weald in southeast England.

Fold Mountains

Distinguished by large-scale folding, fold mountains are caused by lateral compression and simultaneous or subsequent uplift of stratified rocks. Simple fold mountains form where sediments have been folded by sliding over a basement of igneous or metamorphic rocks. The process is somewhat analogous to pushing a carpet lying on a floor up against a wall to form large rumples. Such mountains exhibit sequences of straight, parallel valleys and ridges. The valleys are carved out of the softer rocks, and the more resistant rocks remain as ridges. Examples of fold mountains include the Appalachian Mountains of North America and the Swiss Jura bordering France and Switzerland.

Fault-Block Mountains

The Teton Range, a segment of the Rocky Mountains in Wyoming, consists of fault-block mountains.

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Fractures in the Earth’s surface, a process referred to as taphrogeny, result in formation of fault-block mountains. If there are two parallel faults, the crustal block between them may either rise to produce a horst- block mountain or fall to produce a rift valley. Such a fallen block is called a graben. The term block mountain may be applied to tilted fault-block and complex faulted uplands. Block mountains exist in Nevada, Utah, and Arizona, where they form basin-and-range landscapes. Uplifted blocks may have younger covering formations stripped off them, leaving relict landforms as in the Harz and Black Forest terrains of Germany and in the Massif Central of France.

Volcanic Mountains

Overlapping lava flows and layers of consolidated volcanic dust, called tuff, are responsible for the formation of volcanic mountains. Such stratified volcanoes occur in the Pacific Northwest of North America and in Japan. They are typically steep-sided cones that are built up around a central vent. This conical shape may be modified by lateral eruptions, as in the case of Mount St. Helens in Washington, or by the collapse of the central vent, caused by the withdrawal of magma. This creates a pit called a caldera. Volcanic mountains with calderas are Mount Mazama in Oregon and Krakatoa in Indonesia.

Plateau Mountains

Plateau mountains occur in series when the folds of a mountain chain pass abruptly into the horizontal strata of a basalt plateau that is largely denuded of trees and eroded. These topographic forms are, however, really pseudomountains that are produced by the erosion of a plateau—for example, the Catskill Mountains of New York. These examples occur in association with major plateaus of the world, such as the Colorado and Tibet plateaus and the Altiplanos of South America. Theories of Mountain Formation

Every continent contains two main kinds of building units: shields and mountains. The shield, or craton, is the nucleus of Precambrian rock around which the continent has accumulated. Mountains of intensely folded and faulted strata and volcanic rock surround the cratons. Mountains are formed by various mountain-building processes. In the mid-1800s mountain formation, or orogeny, was thought to include both the deformation of rocks within the mountains and the creation of the mountainous topography. Today, most geologists regard the

formation of mountainous topography as postorogenic. Orogeny is the process by which structures within fold- belt mountainous areas were formed, including thrusting, folding, and faulting in the outer layers of the Earth.

Knowledge of the origin of mountains comes from analysis of geologically young mountain ranges of high elevation, such as the Himalayas and the Alpine ranges of Asia and southeastern Europe. Older and more deeply eroded ranges such as the Appalachians of eastern North America and the Caledonian Belt of northwestern Europe have also provided insight into mountain-building processes. Geologists believe that the younger mountain belts on Earth are related to global tectonics (seegeology). During the last century they developed the geosynclinal theory to account for mountains composed of sediments. According to this concept, extraordinarily thick sediments accumulated in large basins, or geosynclines, are subjected to the compressional forces that produce folds, faults, metamorphism, and eventually a mountain chain. The compressional mountain-building event that occurs in geosynclinal areas is also called an orogeny.

In the framework of plate tectonics, orogeny occurs primarily at the boundaries of colliding plates. At these sites sedimentary deposits on the surface are crumpled, forming folded mountains. Volcanism is initiated, and volcanic belts may form. An example of this type of mountain building occurs along the Pacific coast of South America in the Andes Mountains where the American and Nazca plates collide. The collision of continents may instead produce a mountain range of thickened continental crust. A prime example of the result of a continent- continent collision is the Himalayas, which began forming 25 million years ago when a plate carrying India slid into the Asian plate.

According to the theory of continental drift proposed by the German meteorologist Alfred Wegener, mountains form by crumpling along the leading edge of a drifting continent as it moves through the seafloor. This concept is usually considered a corollary to modern plate-tectonics theory. The forces involved in mountain building are caused by the tectonic deformation of the Earth’s crust. Mountain Climate

Because of their great elevation, mountains affect climate and vegetation in different ways. At similar latitudes, elevation above sea level plays a major role in climatic conditions. Snowfields and glaciers found at high elevations where temperatures rarely rise above freezing are often associated with microclimates. Highland climates have large changes in temperature from night to day. Mountain areas typically have heavier rainfall than the surrounding lowlands. The windward sides of mountains tend to be more cloudy and rainy and have smaller temperature ranges. Leeward sides of mountains are drier, sunnier, and more variable in temperature.

The timberline or tree line is the elevation at which tree growth stops. Its location depends on temperature, soil, drainage, and other factors. The mountain timberline always would be higher near the Equator than near the poles if it were not for the abundant rainfall in equatorial mountains, which lowers the air temperatures. Some of the mountains in the Western United States have two timberlines: a lower, dry timberline and a cold timberline about 2,000 to 4,000 feet (600 to 1,200 meters) above the dry timberline. Forests near the tree line on windward slopes are often stunted and twisted by strong winds into strange shapes known as elfinwood. In the Northern Hemisphere, tree lines are somewhat lower, and vegetation may be denser on the south slopes. Effects on Human Life

Mountainous terrain is often both an asset and a hindrance to humans. Mountains have provided protection from war-minded neighbors. The Swiss have thrived in their mountain environment because it has given them a degree of political independence that is unusual in their part of the world. The high mountains that border

Switzerland on the west and north made it possible for the country to avoid military involvement in both world wars. The Swiss have, however, developed a high standard of living only with prodigious effort, determination, and ingenuity. Mountains have furnished valuable resources of minerals, timber, water, and scenery. Some mountain slopes, like those of volcanoes in Java, Guatemala, and Sicily, have unusually fertile soils for agriculture. The short growing seasons at high altitudes, however, often restrict agriculture to specialized crops such as tea and coffee in lower altitudes and to grazing in higher ones. Mountain dwellers also have to contend with avalanches, landslides, earthquakes, and glacial bursts.

The rigors of mountain living associated with cold temperatures and low oxygen levels and difficulties with construction and maintenance of engineering works have precluded the development of many modern highland cities. One of the highest cities in the United States, Santa Fe, New Mexico, lying at 6,996 feet (2,132 meters) above sea level, compares with the elevation of Mexico City but not with the much older cities in the Andes and Tibet. Potosí, Bolivia, is the world’s highest city at 13,045 feet (3,976 meters). At elevations of 17,500 feet (5,334 meters), atmospheric pressure is reduced to about one half that at sea level. (See also individual articles on major mountains and mountain systems.)

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Rhine River

Physically and culturally, the Rhine River has played a major role in shaping European history. It is also the busiest waterway in Europe. From its source high in the Swiss Alps, the Rhine is about 765 miles (1,230 kilometers) long. The Rhine runs through the most populated part of Europe, and its steamers and barges carry a steady flow of cargoes.

The Rhine River flows through Germany.

The Rhine begins in east-central Switzerland at the juncture of two small mountain streams near Chur, the Vorderrhein and Hinterrhein. Their combined flow bends northward to form the western boundaries of Liechtenstein and part of Austria. The Rhine then turns westward through Lake Constance, northward to form part of the boundary between France and Germany, and westward through the Netherlands. There it branches into many arms that form a wide, flat delta on the coast of the North Sea.

A castle in the upper middle Rhine Valley is both a private residence and a museum open to the…

Contunico © ZDF Enterprises GmbH, Mainz

The Rhine begins in Alpine headwaters, moves through a narrow valley to Cologne and through a great plain to the North Sea. The German part of this plain is laced with industrial cities. Some of the major cities are Schaffhausen, Basel, Mannheim, Worms, Mainz, Wiesbaden, Koblenz, Bonn, Cologne, Düsseldorf, and, in the Netherlands, Rotterdam. The largest tributaries include the Neckar, Main, and Ruhr on the right bank, and the Aare, Moselle, and Erft on the left bank.

Canals link the Rhine with the Rhône, the Marne, the Danube, the Ems, and other navigable rivers. These canals provide transportation and an extensive river trade to ports in Germany, France, Belgium, and the Netherlands. Many barges sail from various North Sea ports to Basel, the head of navigation on the Rhine. Barges carry raw materials that the Swiss use in manufacturing as well as coal, iron ore, petroleum, and grain from the Ruhr valley. Some barges can sail up the Rhine as far as Cologne.

Rüdesheim is a town in the Lorelei Valley, near the Rhine River.

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Magnificent falls near Schaffhausen, Switzerland, generate electricity that powers a large aluminum plant. The Rhine has carved a beautiful 90-mile (145-kilometer) gorge from Bingen to Bonn. Many legends, such as The Lorelei and Song of the Nibelungs, were inspired by the river’s wooded banks. Splendid castles on the rocky heights draw many visitors.

From earliest times the Rhine has been a path of conquest and trade. Prehistoric peoples were thought to have followed its course, and it later became the frontier of the Roman Empire and then the gateway for the

onrushing Germanic tribes. In the Middle Ages the Rhine was the route for the profitable overland trade between Central Europe, Italy, and the Far East. The river served as a major line of German defense during World War II.

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river

The Earth’s rivers carry the water that people, plants, and animals must have to live. They also provide transportation and waterpower. Nations have learned to harness the power of rivers by building hydroelectric dams such as those constructed on the Volga River. Rivers are also a principal natural force in shaping land surfaces. They drain surplus water to the sea, deposit soil and rocks to build new acreage, and erode land formations. Rivers have created such natural wonders as the Nile Delta in Egypt and the Grand Canyon in the United States.

Canoeists travel on the Coosa River near Wetumpka, Alabama.

Jason Martin/Alabama Bureau of Tourism & Travel

The Murray River flows through South Australia.

Rivers and Human Activity

In many ways rivers helped give rise to human civilization. The earliest people built their towns and villages beside the rivers’ flowing waters. Here they found a water supply, a food supply, a means of transportation, and protection from enemies. These settlements often developed into major urban centers of trade and commerce ( seeancient civilization). Most of the great cities of the Middle East, India and Asia, Europe, and North and South America arose beside the largest rivers on the continents.

The settlement of new lands throughout the world followed the course of rivers. Settlers usually traveled to the interior lands by raft or boat or followed trails through river valleys. Fertile valleys made good farmland that was watered and enriched by flowing rivers and streams. Town sites were located where rivers could provide a means of transport for goods and power for mills.

Today people are also dependent upon rivers for much of their water supply. Spreading cities need huge amounts of water every day for industrial and home use. Hydroelectric dams generate millions of volts of electricity that serve the energy needs of modern urban and rural areas. In dry and semiarid lands, water from rivers is used to irrigate acreage for farming. (See alsoirrigation; water; waterpower.)

People have not always been content to let rivers choose their own courses and rates of flow. To get the greatest benefit from these natural resources, people alter rivers through engineering projects. They widen, deepen, and straighten streams to control the speed and flow of the streams’ water. Engineers construct reservoirs, levees, and floodwalls to control flooding. Such projects keep high waters from overflowing and limit the amount of damage done to surrounding towns and farmland. Engineers also build canals with locks and dams so boats navigating rivers can get past falls and rapids. In some cases they dig canals to link rivers with other bodies of water. The St. Lawrence Seaway, which serves as part of the border between the United States and Canada, is one of the best examples of such engineering projects. The seaway is a complex of natural waterways, deepened channels, locks, and canals stretching across 2,342 miles (3,769 kilometers). It links the five Great Lakes in Canada and the United States with the Atlantic Ocean, providing 9,500 miles (15,288 kilometers) of navigable waterways.

Human activities can also be harmful to rivers. Industries such as paper manufacturing and nuclear power require vast quantities of water in their processes. Waste products and heated water discharged from such plants pollute rivers and streams and can damage or destroy plant and animal life that depends on the waterways. Many streams are polluted by sewage or by commercial fertilizers and pesticides that drain into the water from the surrounding land. The destruction of grass and forest in the watersheds has added to the flood problem in some states, muddied the streams, and filled the lakes with silt. In some areas levees or dams built to control flooding have actually made the condition worse. If a river’s flow is slowed too much, the river bed begins to fill with silt, making it shallower and less able to carry the same volume of water. As a result, during times of heavy rainfall the river is unable to handle the added water and overruns its banks more quickly than it did before the levees and dams were built.

How Rivers Flow

Some features of a river and its basin, such as branches and valleys, occur several times in its…

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A river starts as a tiny trickle, or rill, on a slope. Rainfall, snowfall, a spring, or the melting of glacial ice may be its source. As it flows downhill it is joined by other trickles to make a brook. Other brooks add their waters to form a stream, which broadens into a creek. As the water continues its downward journey, it gains in volume and finally becomes a river.

Along its course, the river receives water from inflowing streams called branches, or tributaries. The river and its branches make up a river system. The area that the system drains is its basin. A divide, or watershed, separates the drainage areas of neighboring streams.

Rivers are also fed by groundwater—water that has soaked into the earth instead of running off the surface. This water flows steadily into the river—sometimes through underground springs.

Erosion by the Colorado River has created new landforms.

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Nearly all rivers have an upper, middle, and lower course. Each level has its own characteristics. The upper course begins at higher elevations. Here the river is smaller and usually has a rapid, tumbling flow that cuts a narrow channel through rocky hills or mountains. It may roll large boulders along in its swift current. The river creates waterfalls where it carves out layers of soft rock and leaves a cliff of hard or resistant rock standing. It forms rapids along sloping rocky beds. When a hard rock formation follows a definite line in a region, all the rivers that cross it there have falls. This is called the fall line. When a river reaches a level or a sunken area, it

may form a lake. Over thousands or millions of years the river erodes, or wears away, soil and rocks and carves a canyon or a deep, V-shaped valley. The type of formation it creates depends on the force of the river and the type of material it erodes (seevalley).

When the river descends to lower elevations, it runs more slowly over the gently sloping land of its middle course. Its current no longer has the force to carry stones or gravel. This material drops to the riverbed, where it forms bars of sand or gravel or builds islands. These formations are continually changing shape as the river deposits or erodes material. The formations affect the river in turn by altering its course. River currents swing toward one bank or the other, gradually undercutting the banks and widening a V-shaped valley into a U shape. In the United States, for example, V-shaped valleys are more common in the geologically younger Western states while U-shaped valleys are found in the older regions of the Central and Eastern states.

As the river flows downstream it reaches the still gentler slope of its lower course. It drops more of its load than it did upstream and begins to build up its bed (aggradation) instead of tearing it down (degradation). The valley has been eroded into a wide plain. The river swings in great S-shaped curves, forming loops called meanders.

When a river floods, it may cut across the narrow part of the loop, making a new, shorter channel. The loop is left as a lake known as an oxbow lake. Braided channels appear when the river level falls and exposes bars of sand or gravel. A single meandering channel can become braided downstream from a tight bend in the river, where coarse material is brought up from the river bottom to form sandbars or islands of gravel. The braided river channels typically occur on the edge of land ice or on plains such as the Canterbury Plains of South Island in New Zealand.

At times heavy rain or melting snow rushes from the upper or middle course of a river into the shallow channel of the lower course. The river floods the surrounding country, leaving a thin layer of sediment. Such an event may happen seasonally, as in the annual flooding of the Nile, or only on rare occasions, as in the case of unusually heavy rainfall or snow melt in an area. If the flooding is seasonal, in time the layers of sediment accumulate and build a broad, fertile floodplain, like that along the Mississippi and the Nile. Most of the silt and sand drops nearest the channel, forming a broad embankment, or levee. In time the river may flow on a bed higher than the level of the plain. The fertile soil of floodplains attracts human settlement, but flooding can destroy crops and property along the river. To protect the plain, engineers may deepen the channel by dredging accumulated sediment from the riverbed, or they may build artificial levees, or dikes, to contain the river as it rises (seeflood control).

When the river reaches the sea, it deposits its remaining load of silt, gravel, and sand at its mouth. This material builds an ever-growing triangular-shaped area called a delta. Here the river branches into several distributaries that empty into the ocean. The mixture of fresh and salt water often gives rise to unique plants and animals. If some distributaries become choked with silt or plant life, the river creates new distributaries and enlarges the delta. Wherever a seacoast has sunk at the mouth of a river, the ocean flows into the river valley, forming an estuary. The mouth of the St. Lawrence River is an estuary. Longest rivers in the world

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Rocky Mountains, or Rockies

Rugged and massive, the Rocky Mountains form a nearly continuous mountain chain in the western part of the North American continent. The Rockies sweep down from Alaska through Canada and the western third of the United States. More than 3,000 miles (4,800 kilometers) long, they vary in width from 70 to 300 miles (110 to 480 kilometers) and cover about 300,000 square miles (777,000 square kilometers). Only South America’s Andes are longer.

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Boaters enjoy the scenic beauty of the Rocky Mountains, on the Salmon River in the Frank…

The Rockies are the easternmost part of the Cordillera system. This system, which also includes the Sierra Nevada, the Cascade Range, and the Coast Ranges in North America, extends southward to Cape Horn in South America.

The Sangre de Cristo Range in north-central New Mexico is usually considered the southern end of the Rockies. The chain can be traced farther southward in New Mexico and western Texas through the Sacramento, Davis, and Santiago mountains and on into Mexico’s Sierra Madre Oriental.

Along the crest of the Rockies is the Continental Divide, which separates streams that drain to the east from those that flow to the west. Thus is formed the drainage pattern to the Pacific, to the Atlantic through the Gulf of Mexico, and to the Arctic.

Many major rivers of North America originate in the Rockies. East of the Continental Divide rise the Missouri and two of its tributaries—the Yellowstone and Platte; the Arkansas; the North and South Saskatchewan; the Mackenzie, Peace, and Athabasca; and the Rio Grande. West of the divide begin the Snake, Colorado, Columbia, Fraser, and Yukon rivers. Four Principal Sections

An east-west topographical slice of the western United States at 40° N. latitude shows ranges called …

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From the Great Plains on the east, the Rocky Mountains rise sharply. To the west of the mountains are plateaus and basins. The Rockies may be divided into four principal sections—the Southern, Middle, Northern, and Arctic.

The Southern Rockies

are in New Mexico, Colorado, and Wyoming and are the highest group. Two great parallel folds run north- and southward. In the eastern fold are the Sangre de Cristo Range, principally in New Mexico; the Front Range, west of Denver, Colorado; and the Laramie Mountains in Wyoming. In the Sangre de Cristo Range is the 14,317-foot- (4,364-meter-) high Blanca Peak. In the Front Range are Longs Peak at 14,256 feet (4,345 meters) and Pikes Peak at 14,110 feet (4,301 meters). A spur of the Front Range, the Medicine Bow Range, runs northwestward into Wyoming.

In the western fold are the San Juan Mountains in New Mexico and Colorado and the Sawatch Mountains and the Park Range in Colorado. In the Sawatches is the Rockies’ highest peak, the 14,431-foot (4,399-meter) Mount Elbert. In Colorado 55 peaks soar above 14,000 feet (4,270 meters).

The Middle Rockies

are located in Utah, Wyoming, Idaho, and Montana. They are cut off from the Southern Rockies by the Wyoming Basin, a plateau studded with low mountains. In Utah the Uinta Mountains run east- and westward and the Wasatch Mountains tower near the Great Salt Lake. In Wyoming are the Salt River, Wyoming, and Wind River ranges. The majestic Teton Range is a great block with its eastern face uplifted.

Around Bighorn Basin a giant horseshoe is formed by the Bighorn, Bridger, Owl Creek, and Shoshone mountains and the Absaroka Range. On the Yellowstone Plateau is Yellowstone National Park.

The Northern Rockies

extend into Canada from Montana, Idaho, and Washington about 1,000 miles (1,600 kilometers). On the west is the Columbia Plateau, including the Snake River plain. Running along the Idaho-Montana border is the Bitterroot Range. In Idaho are the Clearwater and Salmon River mountain ranges.

Time-lapse video of construction of the Park Bridge in Kicking Horse Canyon, British Columbia,…

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In Canada the Front Range, or Canadian Rockies, is the most spectacular part of the system. It forms the Continental Divide and the Alberta-British Columbia boundary. Mount Robson, at 12,972 feet (3,954 meters) in British Columbia is the Front Range’s highest peak.

Between the Front Range and ranges to the west is the Rocky Mountain trench. It extends about 900 miles (1,450 kilometers) from Montana northwestward to the headstreams of the Yukon River. West of the trench are the Purcell and Selkirk mountains.

The westernmost ranges of the Northern Rockies in Canada are the Columbias. On their west is the Interior Plateau region of British Columbia. To the north are the Cassiar Mountains.

The Arctic Rockies

are a series of broken parallel ranges. The Mackenzie Mountains extend 500 miles (800 kilometers) northwestward across the Northwest and Yukon territories, and to the east are the Franklin Mountains. Above the Arctic Circle are the Richardson Mountains. The Brooks Range sweeps across northern Alaska.

Along lower slopes of the Rockies the climate ranges from the warmth of New Mexico to the short summers and long, cold winters of northern Canada. The high ranges cool the air blowing across them. Moisture in the air condenses and falls as rain or snow. Since most winds come from the west, precipitation is heaviest on the western slopes; eastern slopes and valleys are often dry.

Each climate supports varied species of plants and animals. The upward limit of tree growth is the timberline. In the mountains are the grizzly bear, bighorn sheep, Rocky Mountain goat, mountain lion, and caribou. In the valleys is the pronghorn antelope.

On the middle slopes are coniferous forests. Three fourths of those in the United States Rockies are designated as national forests, but northern Montana and Idaho are logging centers.

Cattle and sheep graze in valleys during the winter and in mountain meadows in summer. Farming is not extensive in the mountains. Hardy crops, grown mainly in the south, include alfalfa, barley, fruits, potatoes, and wheat.

The Rocky Mountains are rich in copper, gold, silver, lead, and zinc. Also mined are manganese, molybdenum, uranium, and vanadium. Reserves of coal, oil shale, petroleum, and phosphate rock are plentiful. Power plants have been built on mountain streams to supply electricity to mines, towns, and cities.

Many national parks have been established in the Rockies. In the United States are Yellowstone, Glacier, Grand Teton, and Rocky Mountain national parks. In Canada are Jasper, Banff, Yoho, Kootenay, Glacier, Mount Revelstoke, and Waterton Lakes national parks. Waterton Lakes in Canada and Glacier in the United States make up the Waterton-Glacier International Peace Park. History

More than a half billion years ago in the Precambrian era, the core of the Rocky Mountains was formed in ancient ranges, later leveled by erosion. During the Paleozoic and Mesozoic eras the ocean invaded the land and deposited sediments. At the close of the Mesozoic era, during the Cretaceous Period more than 75 million years ago, the growth of the Rockies began. The Appalachian Mountains had already been formed.

How the Rocky Mountains were formed

Encyclopædia Britannica, Inc.

Formation of the Rockies occurred during the Laramide orogeny, which is named for the Laramie Basin in Wyoming, where it was first recognized. There was a tremendous squeezing that uplifted the region in a great series of folds, like wrinkles in a carpet. After the arching, erosion carved away at the mountains. About half of the sedimentary rock was washed off the top of the arch, exposing the hard rock core. On the flanks of the core great quantities of sand and clay were spread to bordering plains and plateaus. This was only one of the cycles of upheaval and erosion that occurred in the region.

Near the end of the Eocene Epoch about 40 million years ago, the Rockies again raised several thousand feet. Volcanoes erupted, most extensively in the Yellowstone Plateau and Absaroka Range. In the early Pleistocene Epoch about 2 million years ago, the region again uplifted.

Through the years streams and rivers cut canyons and deep gorges through the ranges. During the Ice Age snows accumulated on the mountains. Glaciers formed and moved down the valleys, further eroding the mountains. The sculpturing of the Rockies by rain, wind, and ice continues today.

The Rockies were an obstacle for pioneers. Trading posts were built where travel was interrupted. Some of these became cities—such as Cheyenne, Greeley, Denver, and Colorado Springs. Many parties reached the Pacific Ocean by swinging south of the ranges on the Santa Fe Trail. Others followed the North Platte River, then went through the Wyoming Basin and followed the Oregon Trail.

The Lewis and Clark Expedition of 1804 followed the Missouri River to the Rockies, swung southward through valleys, and then crossed the Bitterroot Range. Later, engineers surveyed railroad routes to ease passage through the mountains.

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Sahara

The largest of all deserts is the Sahara. This vast sunbaked land of barren rock, gravel, and shifting sand stretches across northern Africa. Burning sun and scorching winds make it the hottest region in the world in summer. Palm trees and crops can be grown only where there is a spring, a well, or a stream. These fertile spots are called oases (singular, oasis).

Encyclopædia Britannica, Inc.

Palm trees grow around the oasis town of Taghit, Algeria, in the Sahara. The world's largest desert, …

The name Sahara comes from the Arabic word saharaʾ, meaning “deserts.” Almost as large as the entire United States, the Sahara covers 3.5 million square miles (9 million square kilometers). It extends some 3,000 miles (4,830 kilometers) from the Atlantic Ocean to the Red Sea. Southward it spreads an average of 1,000 miles (1,600 kilometers) to the region of the Niger River and Lake Chad in the Sudan. The great desert contains at least a part of Western Sahara, Mauritania, Morocco, Algeria, Tunisia, Mali, Niger, Chad, Libya, Egypt, and Sudan.

The Sahara is one of the Earth’s low-latitude deserts that extend inland from west coasts in and near the tropics. The dry winds that blow over the hot land seldom drop rain except where mountains force the air upward, thus cooling it. Elsewhere rain falls only when a powerful cyclonic storm invades the region, bringing a downpour. In some areas such storms occur only once in ten or more years.

The cloudless sky and dry air expose the land to the piercing tropical sun. A sandy surface may have a temperature of 170° F (77° C) or more. In July the air temperature is more than 100° F (38° C) in many places.

The land cools rapidly when the sun sets. Temperatures may drop as much as 30° to 50° F (17° to 28° C). In winter they may fall below freezing in the north. Ice forms at night.

Dust from Sahara sandstorms may affect weather in distant places.

Contunico © ZDF Enterprises GmbH, Mainz

During the hot days the wind raises little whirlwinds of dust, called “waltzing jinns.” At times a furious, dust- laden wind, called the simoom, sweeps the land.

The Ahaggar Mountains overlook a barren landscape in the central Sahara, in southern Algeria.

Geoff Renner/Robert Harding Picture Library

Much of the Sahara is a series of plateaus. They average 1,000 feet (300 meters) in altitude. Across it from southeast to northwest runs a broad, rocky ridge. This chain reaches its greatest general elevation in the central Sahara, forming the Ahaggar mountain mass. The highest mountains, however, rise in the Tibesti group to the east. Here is the extinct volcano Emi Koussi, the Sahara’s highest elevation at 11,204 feet (3,415 meters).

In the Sahara are various surface formations common to most deserts. Here are rocky uplands, called hammadas, broad stretches of gravel, sand dunes, and basins filled with drifting sand, called ergs. Though the dunes are the most picturesque feature, they occupy only about one eighth of the area. Travel routes avoid them. The Libyan Erg near Egypt holds the greatest mass of dunes on Earth. It covers an area as large as France. The hot sand may give rise to the scorching Egyptian khamsin wind.

The Nile and the Niger rivers cross the edges of the Sahara. There are no other permanent streams. Dry streambeds, called wadis, seam the desert. Travelers are warned against camping in them, however, because the beds may fill with torrents of water during the rare downpours. Some wadis mark the course of underground streams. Vegetation fringes these courses where the water table is near enough to the surface to be reached by plant roots. An oasis develops where the water supply is sufficient to support substantial plant growth.

In the northwestern Sahara, at the base of the Atlas Mountains, runs a narrow strip of green oases. It extends southeast 750 miles (1,207 kilometers) to the foothills of the Ahaggar. Another depression, the Fezzan, lies between the Ahaggar and Tibesti mountain groups, in the southwestern section of Libya.

Despite its dryness, the Sahara has scattered plant and animal life. Shrubs and other plants resistant to evaporation send their long roots toward underground water, and coarse grass grows in widely separated bunches. Soon after the rare rains, a carpet of delicate, quick-blooming flowers is spread. (See alsoplant.)

Mammal species found in the Sahara include the gerbil, desert hedgehog, and other rodents; the aoudad, or Barbary sheep, the Dorcas gazelle, and the Nubian wild ass; the anubis baboon; the spotted hyena; the pale fox, or African sand fox; and the Libyan striped weasel and slender mongoose. The more than 300 bird species found there include water and shore birds in coastal zones and along waterways, and ostriches, owls, eagles, ravens, and guinea fowl in the interior. Frogs, toads, and crocodiles inhabit the lakes and pools of oases. Lizards and cobras live among the rocks and dunes. Desert snails may remain dormant for years between reviving rainfalls. Prehistoric Past

The Sahara was not always a desert, and its climate continues to change.

Contunico © ZDF Enterprises GmbH, Mainz

The Sahara was not always a parched desert as it is today. Throughout the Ice Age, the huge glaciers and ice caps of Europe pushed the zone of temperate climate southward. The Sahara was then a rich grassland and hunting ground for prehistoric people. Relics of these people include stone tools and rock carvings on sheltered cliffs and walls of caves.

These early inhabitants of the region may have been the ancestors of the Berber people of northern Africa. The Berbers are an ethnic group of people who inhabited North Africa prior to the invasion and settlement of the

area by Arabs in the 7th century AD. After the invasions, many Berbers were converted to Islam and assimilated into Arab society. Today, the Berbers live in tribes scattered across the countries of North Africa. The various tribes speak distinct languages—however, all of the Berber tongues are more closely related to ancient Egyptian than to Arabic. Many Berbers speak Arabic as well. (See alsoMoors.)

By early ancient times, the Sahara was dry and hot as it is today. The northern coastal strip supported warlike people who made trouble for their neighbors. Raiders from the Libyan Desert invaded Egypt. The Carthaginians, and later the Romans, had to keep a watchful eye on the Numidians, who inhabited an area roughly correspondent to that of present-day Algeria.

The vast desert barred travel to central Africa. During the days of the Roman Empire, however, people learned to use the camel for desert travel. Berbers from the Mediterranean coast filtered southward. They improved irrigation systems and planted date palms. Arabs with long camel caravans crossed the Sahara to collect ivory and gold, animal skins, and ostrich feathers. They also imported slaves from central Africa.

A Tuareg man leads a camel through Grand Erg Occidental desert in Algeria.

The camel provided a perfect mount for the Tuareg, a pastoral Berber people who dominated much of the central Sahara. Before the arrival of Europeans, the raiding of caravans and travelers was an important means of acquiring goods. The Tuareg also traded with merchant caravans, but the number of these caravans declined as motor vehicles became available. In the late 20th century increasing urbanization and the occurrence of devastating droughts across the savannas bordering the southern Sahara led many Tuareg to abandon their traditional livelihoods of raising and herding livestock. How People Live in the Sahara

Some of the people who live in the Sahara raise crops on irrigated land in an oasis. Others tend flocks of goats, sheep, and camels. These herders find grass for the stock along the desert’s fringe or where sudden rains have fallen. They live in tents so they can move easily as soon as the grass is eaten in one place.

The nomads wear long woolen robes called barracans for protection against the hot sun and stinging sandstorms. They wear turbans wound around the head and neck and sandals to guard their feet on the hot ground. They eat dates from oasis palms and cheese made from the milk of goats and camels. Water is a scarce and precious resource. In the markets of the oasis villages people trade wool, hides, and some of their animals for dates, coffee, and manufactured articles.

Through the centuries palm-shaded oases have been ports of call for thirsty caravans. Here they made stops to rest, pasture, and water their camels. Many oases grew into fortified villages. The larger ones have a citylike appearance, with narrow, roofed-over streets and buildings several stories high.

The spread of modern transportation increased after World War II, when the French began exploring and developing the petroleum and gas resources of Algeria. Pipelines were laid to carry the oil to Mediterranean ports. Caravan trails were changed into roads covered with a tar that withstands the heat. Four such roads cross the desert from north to south. Airports were built at the chief oasis towns and at oil and gas fields. In the late 20th century increased urbanization and devastating droughts across the southern Saharan savannas led many Tuareg to abandon their traditional pastoral lifestyles.

Modern Developments

The discovery of petroleum and natural gas reserves in Algeria attracted international interest in exploring and developing the Sahara. Soon other oil and natural gas fields were discovered in Egypt and Libya, and large deposits of such minerals as iron ore, copper, and manganese were found as well. Uranium is widely distributed in the Sahara and has been particularly important in Niger.

In 1960 France began testing nuclear weapons in the Algerian desert. After protests from African nations, the test site was abandoned. An agreement for Algerian independence, signed on March 18, 1962, included arrangements for joint control over Algerian oil fields and a split of the profits from all petroleum sales. There was large-scale development and population expansion of the Sahara in the 1960s.

A severe drought in the late 1960s and early 1970s, caused by vastly increased numbers of livestock and their subsequent overgrazing of the land, devastated the region’s economy. Agricultural programs implemented in the 1980s at the Sabha and Al-Kufrah oases in Libya produced good crops of wheat and fruits.

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Snowy Mountains

The highest mountain in Australia, Mount Kosciuszko, is one of the Snowy Mountains. This range, often called the Snowies, is part of the Australian Alps in eastern Victoria and southeastern New South Wales. The Snowy Mountains contain several peaks that are more than 7,000 feet (2,100 meters) high. Mount Kosciuszko rises 7,310 feet (2,228 meters) above sea level. The Snowy Mountains are also the site of a large hydroelectric power project.

Eucumbene dam impounds a lake on the Snowy River, in New South Wales, Australia. The dam is central…

G.R. Roberts

The area is known for winter sports and for Kosciuszko National Park. The mountains are snow-covered for three to six months of the year, and several rivers rise on their slopes. The Murray, Murrumbidgee, and Tumut rivers flow inland. The Snowy River used to flow southward to Bass Strait, but the Snowy Mountains Hydro-electric Authority changed its direction.

Learn about the Snowy Mountains Scheme in southeastern New South Wales, Australia.

Workers install reinforcing steel during construction of one of the dams within the Snowy Mountains…

National Archives of Australia: A1200, L49630

This organization was established in 1949 to manage the Snowy Mountains Scheme. The massive project, built over 25 years, diverts the Snowy River through tunnels in the mountains to join the Murray and Murrumbidgee rivers. Reservoirs and dams collect the water to generate electric power and for use in irrigation. The scheme is now managed by a government-owned company called Snowy Hydro.

The first inhabitants of the Snowy Mountains were Aboriginal groups, including the Ngarigo, Walgalu, and Southern Ngunnawal peoples. European settlers arrived in the early 1800s. In 1840 Polish explorer Paul Strzelecki led an expedition into the mountains. He climbed the highest peak and named it Mount Kosciuszko in honor of Tadeusz Kosciuszko, a Polish patriot and statesman.

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Table Mountain

At the southern tip of Africa, a flat-topped mountain called Table Mountain overlooks Table Bay and the city of Cape Town, South Africa. The mountain dominates the northern end of the high, rocky Cape Peninsula. One of the most recognized landmarks of Cape Town, Table Mountain is often used as a symbol of the city and of South Africa. On cloudless days the mountain can be seen from about 125 miles (200 kilometers) away at sea. The mountain is part of Table Mountain National Park and is a popular tourist attraction, offering hiking, camping, and other activities. Since 1929 visitors have been able to take a cable car to the top. The Kirstenbosch National Botanical Garden is located on the mountain’s eastern slopes.

Table Mountain overlooks Cape Town and Table Bay, in Western Cape province, South Africa.

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Table Mountain is formed from nearly horizontal layers of sandstone. Vigorous wind and water erosion have exposed the layers, giving the mountain its tablelike appearance. The mountain is about 2 miles (3 kilometers) long. Its bare, rocky sides contrast with the fertile top, where many plants grow. The mountaintop also has small valleys, streams, and waterfalls. The highest point is a man-made pile of stones called Maclear’s Beacon, which was built by Sir Thomas Maclear in the 19th century. This point is 3,563 feet (1,086 meters) above sea level and is located on the northeastern side of the mountain.

There are two peaks next to Table Mountain. To the northwest is Lion’s Head, which rises to 2,195 feet (669 meters). It is linked to another hill, known as Signal Hill or Lion’s Rump. To the northeast of Table Mountain is Devil’s Peak, which is 3,281 feet (1,000 meters) high. It was previously called Windy Mountain. To the west, on the Atlantic Ocean side of Table Mountain, are a series of peaks known as the Twelve Apostles.

Table Mountain has its own cloud cover, which is called the Tablecloth. The clouds form rapidly when the wind is in the southeast. Rain from these clouds is mainly responsible for the lush vegetation on the mountaintop. Five mountain reservoirs catch the rainfall brought by northwesterly winds in winter.

Lush vegetation grows at Kirstenbosch National Botanical Garden, on the eastern slopes of Table…

Harvey Barrison

The plant life on Table Mountain is very diverse—the mountain has more plant species than Great Britain. More than 250 kinds of daisies grow on the mountain. Also among the many wildflowers is the red disa, an orchid known as the “pride of Table Mountain.”

There were once many wild animals on Table Mountain, including the Cape lion, the leopard, and the buffalo. Now only small mammals remain, such as monkeys, dassies (hyraxes), and small gray mongooses. The mountain is also home to tahrs, or Himalayan goats, that are descended from escapees of a local zoo.

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Thames River

Not for its length but for its location is the Thames one of the best-known rivers in the world. Although it is only 210 miles (338 kilometers) long, it is England’s chief waterway. The Thames begins at Seven Springs in the Cotswold Hills. From there it pursues a very winding course through the Chiltern Hills. At Oxford, the famous university town, it is met by its chief western tributary, the River Cherwell. This is the end of commercial navigation. From here the river flows through the English countryside, passing such well-known sites as Henley, where the annual regatta is held; the royal residence at Windsor Castle; the college town of Eton; Hampton, famous for its beautiful Hampton Court palace built during the reign of Henry VIII; and then on to London.

An aerial view of the Thames Barrier at Woolwich shows the gates in defense position, holding back…

Rendel Palmer & Triton and Greater London Council

By the time the Thames reaches London, it has become an estuary, an arm of the North Sea affected by the tides. The river flows for 25 miles (40 kilometers) through Greater London, past the Tate Gallery, Lambeth Palace, the houses of Parliament, the Royal Festival Hall and National Theatre complex, Southwark Cathedral, and the Tower of London. Below the Tower Bridge, one of 18 road bridges that cross the Thames in the Greater London area, there are many docks, large numbers of them no longer in use. These have received ships from all parts of the world on one of Europe’s busiest waterways. Here, as the river widens, bridges are replaced by tunnels.

Down river is Greenwich, noted as the prime meridian (zero longitude) for the world’s mapmakers and navigators. By the time the Thames reaches Gravesend well to the east of London, it is more than 700 yards (640 meters) wide. At its widest, where it flows into the North Sea, it is 5.5 miles (8.9 kilometers) wide. The river officially ends at the lighthouse at Nore, where it enters the North Sea. Tides of the North Sea have long affected the water level of the river, sometimes triggering disastrous floods. To counter this threat, Parliament in 1972 passed the Barrier Act authorizing the construction of the Thames Barrier at Woolwich, east of London. It became operational in 1982.

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Uluru/Ayers Rock

One of Australia’s most famous landmarks, Uluru/Ayers Rock is a giant mass of weathered sandstone located in the southwestern part of the Northern Territory. It is of great cultural significance, as shallow caves at the base of the rock are sacred to several Aboriginal peoples. Within the caves are many Aboriginal carvings and paintings. The rock is part of the larger Uluru–Kata Tjuta National Park (formerly Ayers Rock–Mount Olga National

Park). The park was declared a UNESCO World Heritage site in 1987 and is among Australia’s most popular tourist destinations.

Uluru/Ayers Rock is one of Australia's most famous landmarks.

Encyclopædia Britannica, Inc.

Uluru/Ayers Rock is one of the best-known symbols of the Australian landscape. It is a massive…

Paul Steel/Photo Index

Weathering has carved many grooves and shallow caves into Uluru/Ayers Rock, in Australia's Northern…

Uluru/Ayers Rock is composed of a type of coarse-grained sandstone known as arkose. The rock appears in different shades of pinks, reds, oranges, and browns depending on the position of the sun. At sunset it is a fiery orange-red. One of the largest rocks in the world, it rises 1,100 feet (335 meters) above the surrounding desert plain. Roughly oval in shape, it is about 2.2 miles (3.6 kilometers) long by 1.5 miles (2 kilometers) wide. Over time, rain and wind have eroded the rock, leaving the lower slopes fluted and the top carved by gullies and basins. After rainstorms (which are infrequent in this arid region), the gullies and basins produce large waterfalls.

The rock has long been known to the Aboriginal peoples who live in the area. The Aboriginal name for the rock is Uluru. The first nonindigenous Australian to see the rock, in 1873, was the explorer William Gosse. He named the

rock Ayers after the former South Australian premier Sir Henry Ayers. In 1985 the government granted official ownership of the rock to Aboriginal people, who then leased the rock and the national park to the government for 99 years. The rock’s name was officially changed to Ayers Rock/Uluru in 1993 and to Uluru/Ayers Rock in 2002.

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Three Sisters

The scenic Three Sisters rock formation rises above a cliff in the Blue Mountains. The mountains, which form a section of Australia's Great Dividing Range, are located in New South Wales.

David Johnson

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Beardmore Glacier

The enormous Beardmore Glacier extends across the Transantarctic Mountains of central Antarctica.

Commander Jim Waldron USNR—Antarctic Photo Library/National Science Foundation

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Australia: rainforest

The Daintree Rainforest on the north-eastern coast of Queensland, Australia, is an ancient forest. It is thought to be more than 100 million years old.

Dinkum

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Dandarah, Egypt: sugarcane

A stand of sugarcane on the west bank of the Nile River, near Dandarah, Egypt.

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Grand Canyon

The colorful buttes, ravines, and rock formations in the immensity of the Grand Canyon are impressive when viewed at sunrise from Yavapai Point.

Bob Thomason/Stone

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Murray River

The Murray River is the principal river of Australia. It flows across the southeastern part of the country, from the Snowy Mountains to the Great Australian Bight of the Indian Ocean.

Picturepoint, London

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United States

Cliffs line the north-west coast of the island of Kauai, Hawaii.

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Uluru/Ayers Rock

Uluru/Ayers Rock is one of the best-known symbols of the Australian landscape. It is a massive weathered rock in the Northern Territory that rises some 1,100 feet (335 meters) above the desert plain.

Paul Steel/Photo Index

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spinifex grass: Great Victoria Desert

Spinifex grass grows in the Great Victoria Desert of southern Australia.

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Cradle Mountain–Lake St. Clair National Park

Cradle Mountain overlooks Dove Lake, in Cradle Mountain–Lake St. Clair National Park, in Tasmania, Australia. The national park is part of the Tasmanian Wilderness, a UNESCO World Heritage site.

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Nambung National Park: Pinnacles, Australia

The Pinnacles, an area of Nambung National Park, in Western Australia, is known for its unusual limestone formations.

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Thailand

Mangrove trees can be seen at low tide on the coast of Thailand.

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Barbados: rock formations on a beach

Rock formations jut out of the water on a beach near Bathsheba, Barbados.

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Barbados: rock formations on a beach. Image. Britannica LaunchPacks: Landforms and Landscapes, Encyclopædia Britannica, 19 Feb. 2021. packs-ngl.eb.com.au. Accessed 6 Aug. 2021.

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river: chief parts of a river and its basin

Some features of a river and its basin, such as branches and valleys, occur several times in its course. As it approaches its mouth, the river becomes wider and tends to flow more slowly.

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River: chief parts of a river and its basin. Image. Britannica LaunchPacks: Landforms and Landscapes, Encyclopædia Britannica, 19 Feb. 2021. packs-ngl.eb.com.au. Accessed 6 Aug. 2021.

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Great Barrier Reef

The Great Barrier Reef, off the coast of north-eastern Australia, is one of the natural wonders of the world.

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Great Barrier Reef. Image. Britannica LaunchPacks: Landforms and Landscapes, Encyclopædia Britannica, 19 Feb. 2021. packs-ngl.eb.com.au. Accessed 6 Aug. 2021.

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Transantarctic Mountains

The Transantarctic Mountains divide Antarctica into eastern and western parts. The mountains stretch from Victoria Land to the Weddell Sea.

Hannes Grobe

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Transantarctic Mountains. Image. Britannica LaunchPacks: Landforms and Landscapes, Encyclopædia Britannica, 19 Feb. 2021. packs-ngl.eb.com.au. Accessed 6 Aug. 2021.

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Australia: Outback

Video Transcript

NARRATOR: The term “Outback,” or “the bush,” defines any part of Australia removed from the more-settled edges of the continent. In other words, it is “out back” from the larger cities that reside on Australia’s coasts. The Outback is typified as arid or semiarid, open land, often undeveloped. From space we see it as a vast reddish landscape. One can fly roughly 2,000 miles between Sydney and Darwin without seeing anything but the most-scattered and minute signs of human habitation. The Great Sandy Desert is one such part of the Outback. Maps of this land sometimes designate areas as lakes, but many such lakes are dry.

Much of Australia consists of land known as the Outback, or “bush.”

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Australia: Outback. Video. Britannica LaunchPacks: Landforms and Landscapes, Encyclopædia Britannica, 19 Feb. 2021. packs-ngl.eb.com.au. Accessed 6 Aug. 2021.

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Tulum

Video Transcript

narrator] The Yucatán Peninsula should be avoided by anyone who doesn't want to risk becoming addicted to] the laid-back way of life. The sandy beaches and palm-lined bays of the Mayan Riviera can be very moreish. Tulum, around 130 kilometers from the tourist resort of Cancún, was a trading hub during the Mayan civilization. It experienced its heyday in the years 1200 to 1400 A.D., before the Spanish conqistadores arrived in the Yucatán. It is no surprise that the Mayan gods chose to live here. The Maya called this picturesquely situated city Zama, which translates as the City of Dawn. Tulúm is the only Mayan site located right next to the ocean. El castillo is the largest and probably the most important building in Tulum. It was constructed over a number of different epochs and incorporates many different styles, as becomes clear when one walks around it. Tourists visiting the site are treated to displays by actors who attempt to recreate elements of the fascinating Mayan culture. Tulum is the most-photographed Mayan site in Mexico. Although the site is not of great interest to archaeologists, tourists love it - mainly because of its particularly beautiful setting. The history of the Maya is a fascinating and complex tapestry of fact and legend. In their heyday the Maya were a highly civilized people, known for their cultivation of maize, their mathematical skills, their architecture and their sophisticated calendars recorded in hieroglyphics. Tourists in Tulum get the opportunity to experience one particular feature of the Mayan culture: its rituals. Today they are being treated to a re-enactment of the fire ceremony. The New Fire ceremony was performed once every 52 years - a full cycle of the calendar. The priests and warriors celebrated the New Fire in an elaborate performance that they believed would stave off the end of the world. It is fascinating to witness the recreation of these mysterious rituals from Tulum's past, when it was the city of Zama. But the ancient port of the Mayan civilization is now a tourist attraction, situated in a place where, today, the quintessential Caribbean way of life is celebrated: chilling under palm trees.

Tulum is a Mayan site on the Caribbean coast.

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Tulum. Video. Britannica LaunchPacks: Landforms and Landscapes, Encyclopædia Britannica, 19 Feb. 2021. packs-ngl.eb.com.au. Accessed 6 Aug. 2021.

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Whitsunday Island

Video Transcript

This ferry here on Hamilton Island just off of Australia's East Coast is a luxury liner in its own right befitting the exclusive destination, Hayman Island, the most northerly of the so-called Whitsunday Islands. This a hotel resort getaway beyond compare. The Whitsunday Islands are considered by many to be the crown jewels of the Great Barrier Reef. Snow-white sandy beaches and immaculately clear turquoise waters are to be found on nearly all of the 74 islands. However, only a few of the of them are inhabited and offer hotel and resort facilities like those of Hayman Island. The best way to explore this veritable string of pearls in the Pacific is naturally by boat. The largest of the uninhabited islands is Whitsunday itself, home of the world-famous Whitehaven Beach and a popular stop off point for many sailing ships that pass this way. People eager to follow in the footsteps of Robinson Crusoe can be voluntarily marooned here for the night. The islands are surrounded by coral but its quality and beauty can't compare with that of the reefs further north or east of here. If you're interested in diving on the Whitsunday Islands, the Outer Reef located 60 and 80 kilometers off the coast has crystal-clear waters and views to match. No sooner have you taken the plunge than you find yourself in one of the world's most fascinating underwater habitats. Indeed, the Great Barrier Reef was established as a national marine park in 1975 and its wonders have been protected ever since. Even so, tourists are asked to take special care when diving or snorkelling in these parts as many unintentionally damage sections of coral every year. Between August and January is the best time to get an intimate look at the Great Barrier Reef. And you needn't be scared of the larger fish - the majority of these creatures are perfectly friendly towards their visitors.

Whitsunday Island is an island in the Great Barrier Reef, off the eastern coast of Australia.

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Whitsunday Island. Video. Britannica LaunchPacks: Landforms and Landscapes, Encyclopædia Britannica, 19 Feb. 2021. packs-ngl.eb.com.au. Accessed 6 Aug. 2021.

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Follow tributaries from Andean mountaintops as they form the Amazon River and empty into the Atlantic

Video Transcript

NARRATOR: The Amazon River has its beginnings high in the Andes, where countless rivers course down the eastern slopes of the mountain range. Powerful rushing streams surge eastwards from Colombia, Ecuador, Peru, and Bolivia. In Brazil the current slows as the rivers meander along the gentle slopes of the Amazon basin. These rivers merge to form the largest river in the world—the Amazon. On its way to the Atlantic, the Amazon and its tributaries flow through vast lowlands containing more than half the tropical rainforest left on earth.

Streams of the Andes Mountains converge, eventually forming the Amazon River.

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Follow tributaries from Andean mountaintops as they form the Amazon River and empty into the Atlantic. Video. Britannica LaunchPacks: Landforms and Landscapes, Encyclopædia Britannica, 19 Feb. 2021. packs-ngl.eb.com. au. Accessed 6 Aug. 2021.

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Sail down the Nile River from eastern Africa and learn about its importance to the development of North Africa

Video Transcript

NARRATOR: The Nile River travels over 6,000 kilometers, flowing northward from its source—a group of lakes in eastern Africa—through the dry Sahara and finally to the Mediterranean Sea. Each year, the Nile floods, leaving great silt deposits along its banks and the adjacent flatlands. In the past this made the Nile Valley, particularly the Nile Delta, one of the most fertile areas of North Africa. Over a hundred varieties of grasses grow along the river's banks. Today the Nile is the major waterway of North Africa, vital for the transportation of people and goods.

An overview of the importance of the Nile River to the development of North Africa.

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Sail down the Nile River from eastern Africa and learn about its importance to the development of North Africa. Video. Britannica LaunchPacks: Landforms and Landscapes, Encyclopædia Britannica, 19 Feb. 2021. packs-ngl. eb.com.au. Accessed 6 Aug. 2021.

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Explore one of the world's driest regions and learn why parts of Chile's Atacama Desert never see rainfall

Video Transcript

.NARRATOR: Along the coastline of northern Chile lies the Atacama Desert, one of the driest regions in the world Due in part to the effects of the Peru Current, there are areas in the Atacama Desert where no rainfall has ever been recorded.

Atacama Desert, Chile.

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Explore one of the world's driest regions and learn why parts of Chile's Atacama Desert never see rainfall. Video. Britannica LaunchPacks: Landforms and Landscapes, Encyclopædia Britannica, 19 Feb. 2021. packs-ngl.eb.com. au. Accessed 6 Aug. 2021.

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mountains

Video Transcript

Music in] NARRATOR: Mountain relief features are recognizable for their high altitudes and their slopes, some] steeper than others. All continents have mountains. Generally, we distinguish two types of mountains, according to their age. Young mountains, created several dozen million years ago, have steep slopes and high-pointed peaks. The youngest mountains, also the highest in the world, are within the Himalayas massif in Asia. Old mountains, in contrast, have rounded peaks and slopes made gentler by hundreds of millions of years of erosion. For example, the Caledonides in Norway are more than 300 million years old. During new geological events, the basement rock of old mountains may be uplifted again. For instance, some rocks in the Alps were once part of the Hercynian massif, a very old mountain chain that is now eroded. [Music out]

Young mountains have steep slopes and high, pointed peaks. Old mountains in contrast have rounded peaks and slopes made gentler by hundreds of millions of years of erosion.

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Mountains. Video. Britannica LaunchPacks: Landforms and Landscapes, Encyclopædia Britannica, 19 Feb. 2021. packs-ngl.eb.com.au. Accessed 6 Aug. 2021.

While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions.