217 résultats pour "rivers"

• Uzbekistan - country.

  E Environmental Issues The evaporation of the Aral Sea is one of the worst ecological disasters in the world. The Aral has shrunk so much that it now holds only about one-fifth the volume ofwater it held in 1960. The shrinkage is due to irrigation withdrawals from the Amu Darya and Syr Darya, a practice that began on a massive scale in the early 1960s aspart of the Soviet Union’s ill-conceived drive to increase cotton yields in Central Asia. Growing cotton in the naturally arid and saline soil...

• Sri Lanka - country.

  acacias, and orchids are found in many areas. The animal life of Sri Lanka includes 88 species of mammals, 21 of which are threatened with extinction. The Asian elephant, cheetah, leopard, and several species ofmonkey are endangered and officially protected. The island’s many species of primates include the long-tailed langur, toque macaque, and slender loris. Other mammalsinclude the sloth bear, several species of deer, mongoose, and wild boar. Reptiles are numerous, with 144 known species. Som...

• Hungary - country.

  Northern Hungary lacks sufficient water, especially between July and October, when precipitation levels are typically low. Canals irrigate the Great Hungarian Plain,which is subject to drought. Because of the country’s mainly flat terrain, only limited water resources can be harnessed for hydroelectric power. F Environmental Issues Rapid industrialization in Hungary following World War II contributed significantly to a number of major environmental problems, including air, water, and soil pollu...

• Austria - country.

  Wildlife is generally scarce in Austria. Chamois, deer, and marmot are still present; bear, which were once abundant, are now almost completely absent. Hunting isstrictly regulated to protect the remaining species. F Environmental Issues Industrial emissions, a high volume of tourist traffic, and significant air pollution from other countries—principally the former East Germany, Slovakia, and the CzechRepublic—combine to make acid rain the major environmental problem in Austria. One-quarter of...

• Massachusetts - geography.

  mi). Other large artificial lakes include Wachusett Reservoir, East Brimfield Reservoir, and Cobble Mountain Reservoir. Assawompsett Pond, covering about 10 sq km(about 4 sq mi), is the largest natural lake. North Watuppa Pond and Long Pond are other large natural lakes. Lake Chaubunagungamaug, near Webster, is usuallycalled Webster Lake, because the Algonquian name is difficult to pronounce and spell. The full version of the Native American name is said to be the longest place-namein North Amer...

• Congo (river) - Geography.

  region as Portuguese territory, leaving a marble shaft on the riverbank as proof of his discovery. To Europeans the river became known as the Rio de Padrão (Pillar River). The Kongo king welcomed Cam and subsequent Portuguese explorers and established friendly trading relations with the Portuguese. More than 300 yearselapsed before serious exploration of the Congo was undertaken. Francisco José de Lacerda, a Portuguese explorer, reached the copper-rich Katanga region from the east in 1798, as...

• Arctic - Geography.

  The Arctic is not a frozen desert devoid of life on land or sea, even during the cold, dark winter months. Spring brings a phenomenal resurgence of plant and animal life.Low temperatures are not always the critical element—moisture, the type of soil, and available solar energy are also extremely important. Some animals adapt well toArctic conditions; for instance, a number of species of mammals and birds carry additional insulation, such as fat, in cold months. Arctic summers with extended dayli...

• North America - Geography.

  D Climate Although North America has considerable climatic variety, five principal climatic regions can be identified. The northern two-thirds of Canada and Alaska, as well as all ofGreenland, have subarctic and arctic climates, in which long, dark, bitterly cold winters alternate with brief, mild summers. Most of the region, which receives relativelylittle precipitation, is covered with snow and ice during much of the year. A second climatic region is made up of the eastern two-thirds of the U...

• Manitoba - Geography.

  E Plant Life Forests cover 66 percent of Manitoba. The main forest area is divided into the boreal forest and the mixed-wood forest. The boreal, or northern, forest containsconiferous (cone-bearing) trees, especially white and black spruce, balsam fir, and jack pine. South of the boreal forest is the mixed-wood forest, which contains conifers as well as such deciduous trees as white birch, aspen, poplar, and Manitoba maple. Prairie land is found in the southwest, where the natural vegetation i...

• Manitoba - Canadian History.

  E Plant Life Forests cover 66 percent of Manitoba. The main forest area is divided into the boreal forest and the mixed-wood forest. The boreal, or northern, forest containsconiferous (cone-bearing) trees, especially white and black spruce, balsam fir, and jack pine. South of the boreal forest is the mixed-wood forest, which contains conifers as well as such deciduous trees as white birch, aspen, poplar, and Manitoba maple. Prairie land is found in the southwest, where the natural vegetation i...

• Vermont - geography.

  Forests cover 78 percent of Vermont. Most of the trees are deciduous, principally the maple, elm, birch, beech, oak, hickory, ash, cherry, and butternut. The state treeis the sugar maple, which provides Vermont’s famous maple syrup. Conifers are common in some mountain areas and include mainly the white pine, red spruce,hemlock, and cedar. A great variety of ferns have been found within the state. Among the more common wildflowers that grow in Vermont are anemones, arbutuses,violets, lilacs, dai...

• Vermont - USA History.

  Forests cover 78 percent of Vermont. Most of the trees are deciduous, principally the maple, elm, birch, beech, oak, hickory, ash, cherry, and butternut. The state treeis the sugar maple, which provides Vermont’s famous maple syrup. Conifers are common in some mountain areas and include mainly the white pine, red spruce,hemlock, and cedar. A great variety of ferns have been found within the state. Among the more common wildflowers that grow in Vermont are anemones, arbutuses,violets, lilacs, dai...

• Ship. I INTRODUCTION Ship, vessel that is buoyant in the water and used

  B1 Biremes Experience soon proved that longer ships posed a new set of problems: They were weaker structurally, more difficult to maneuver, and presented a larger target to anyenemy ship with a ram. In the 8th century BC Mediterranean shipbuilders eliminated these problems with the bireme , a war galley built to accommodate two levels, or banks , of oarsmen. Oarsmen on the lower level rowed oars from ports cut into the side of the vessel, while those above rowed from the deck. This arrangemen...

• Cameroon - country.

  seminomadic herders of the north. Cattle, goats, and fowl are the most commonly raised animals. B Forestry and Fishing Timber is traditionally one of Cameroon’s most valuable exports, consisting mainly of mahogany, ebony, and teak. The timber cut in 2006 amounted to 11.4 million cu m(401 million cu ft). Most of the fish caught in Cameroon come from the country’s rivers and lakes and are consumed locally. However, deep-sea fishing activity isincreasing, especially from the port of Douala. Some 1...

• Bulgaria - country.

  E Climate Most of Bulgaria has a continental climate, with cold winters and hot summers. The climate in general is more severe than in other European areas of the samelatitudes, and the average annual temperature range is greater than that of neighboring countries. Severe droughts, frosts, winds, and hail storms frequently damagecrops. A Mediterranean climate, with dry summers and mild, humid winters, prevails in the valley of the southwestern Rhodope Mountains; the northern limit of theclimati...

• Guatemala - country.

  C Climate The climate of Guatemala varies according to elevation, from hot coastal plains to cold mountain heights. Most of the population lives between 900 and 2,400 m (3,000and 8,000 ft) above sea level, where there are warm days and cool nights with average annual temperatures of 20°C (68°F). The coastal regions are hot and humid,with average annual temperatures of 28°C (83°F). A rainy season, from May through October, is sometimes called “winter” because it brings cloudy afternoons andlower...

• Azerbaijan - country.

  second most important industrial center after Baku. A Ethnic Groups Azerbaijan, including the autonomous exclave of Naxçivan, is populated mostly by ethnic Azerbaijanis, who are also known as Azeris. The ethnic composition of thecountry changed due to a civil war between the government of Azerbaijan and Armenian secessionists in the Nagorno-Karabakh enclave. Beginning in 1988, when thepeople of Nagorno-Karabakh unilaterally decided to secede from Azerbaijan, nearly the entire Azerbaijani popula...

• Georgia (country) - country.

  1917. During the subsequent Soviet period, religious practice was strongly discouraged because the Soviet state was officially atheistic; however, the GeorgianOrthodox Church was allowed to function openly. Orthodox Christianity is the religion of about 58 percent of the Georgian population. Muslims represent about 19 percent of the country’s population, with ethnicAzerbaijanis, Kurds, and Ajars comprising the principal Muslim groups. Ajars are ethnic Georgians who converted to Islam in the 17th...

• Environment.

  escape into space of the infrared energy radiated back out by Earth. This process is referred to as the greenhouse effect. These gases, primarily carbon dioxide,methane, nitrous oxide, and water vapor, insulate Earth’s surface, helping to maintain warm temperatures. Without these gases, Earth would be a frozen planet with anaverage temperature of about -18°C (about 0°F) instead of a comfortable 15°C (59°F). If the concentration of these gases rises, they trap more heat within theatmosphere, caus...

• Bolivia - country.

  E Plants and Animals Because of the wide variations in elevation, plant and animal species of nearly every climatic zone are found in Bolivia. A coarse grass, called ichu, grows on the largelybarren high plateau in the west. Para rubber trees, more than 2,000 species of hardwood trees, and vanilla, sarsaparilla, and saffron plants are common in the tropicalforests of the east. The llama, found chiefly on the Altiplano, is an efficient beast of burden. Alpacas and vicuñas also inhabit the platea...

• Europe .

  D Vegetation Although much of Europe, particularly the west, was originally covered by forest, the vegetation has been transformed by human habitation and the clearing of land.Only in the most northerly mountains and in parts of north central European Russia has the forest cover been relatively unaffected by human activity. On the otherhand, a considerable amount of Europe is covered by woodland that has been planted or has reoccupied cleared lands. The largest vegetation zone in Europe, cuttin...

• Europe - Geography.

  D Vegetation Although much of Europe, particularly the west, was originally covered by forest, the vegetation has been transformed by human habitation and the clearing of land.Only in the most northerly mountains and in parts of north central European Russia has the forest cover been relatively unaffected by human activity. On the otherhand, a considerable amount of Europe is covered by woodland that has been planted or has reoccupied cleared lands. The largest vegetation zone in Europe, cuttin...

• Ecosystem.

  work. The tiny bacteria and fungi feed upon the remains of the salmon. They break down the salmon intochemical nutrients. Nutrients from the salmon go into the soil. The roots of plants along the riverbank take up the nutrients. They use the nutrients to make food. Inthis way, nutrients get recycled back through the ecosystem. WHAT CAN HARM AN ECOSYSTEM? Any change in one living or nonliving part of an ecosystem can cause changes in other parts. Droughts,storms, and fires can change ecosystems....

• Reptiles.

  to find mates. A male turtle may stroke a female’s face with his front limbs. Most female reptiles make nests and lay eggs. A few lizards and snakes give birth to live young. All baby reptiles can live on their own as soon as they hatch. But most baby reptiles do not live morethan a few months. Birds, snakes, and mammals eat them. Sharks hunt baby sea turtles. Reptiles can live a long time if they don’t get eaten. Some tortoises may live up to 150 years. Alligatorscan live more than 70 years. Sm...

• Mfecane.

  The Kololo, a Sotho people, entered the same region in the early 1820s after being driven from their homeland south of the Vaal River by the Ngwane-Hlubi wars. In1823 the Kololo clashed with the Griqua and turned north into the Kalahari Desert. They eventually crossed the Zambezi and finally settled in what is now westernZambia after overthrowing the powerful Lozi Kingdom in 1840. D Founding of the Sotho Nation The Ngwane-Hlubi wars also drove loosely organized Sotho communities north into the...

• Gold - chemistry.

  producers of gold during this period. Spain's domination in South America resulted, in the 16th century, in a large increase in gold produced in the New World; someresulted from simple seizure of gold from the Native Americans, who had long mined the metal. In the same century Mexico contributed about 9 percent of the totalworld production. Gold was discovered in Australia in February 1851, and rich fields were found there. By the middle of the 19th century the United States produced a considera...

• Central African Republic - country.

  Manufacturing activity in the Central African Republic is very limited. Products include cottonseed, peanut, and sesame oils; textiles; leather goods; tobacco products;soap; flour; bricks; and paint. The output of electricity in 2003 was 106 million kilowatt-hours, 80.19 percent of which was generated in hydroelectric installations. Gemdiamonds account for nearly all the country’s mineral output and two-thirds of its export revenue. Production was 250,000 carats in 2004. Uranium was discovered i...

• Houston - geography.

  Prominent historical and cultural institutions include the Civic Center Complex, located in the central business district. The complex is composed of the George R. BrownConvention Center; the Wortham Center, which is the home of the Houston Grand Opera and the Houston Ballet; and the Jesse H. Jones Hall for Performing Arts, whichis the home of the Houston Symphony. The nearby Alley Theatre houses a professional repertory acting company. Among other local professional performance groupsare the Ma...

• Seal (mammal) - biology.

  remote lakes by swimming thousands of kilometers up rivers from the Arctic Ocean. A few other species such as ringed seals and harbor seals have been found livingyear-round in lakes and rivers near the coasts of Russia, Canada, and Alaska. IV DIET OF SEALS Most seals eat fish and sometimes squid. The leopard seal, an Antarctic species, may have the most diverse diet of all, commonly hunting penguins and other seabirds,smaller seals, as well as fish, squid, krill (small shrimplike crustaceans),...

• Sudan - country.

  B Principal Cities and Political Divisions The principal city is Khartoum, the capital; other major cities include Omdurman and Khartoum North, major industrial centers, and Port Sudan, a seaport on the RedSea. Sudan is divided into 26 states. C Religion and Language About 70 percent of the people of Sudan are Muslims, some 15 percent are Christians, and most of the remainder follow traditional religions. The people of northernSudan are predominantly Sunni Muslims (Sunni Islam). Most of the pe...

• Cambodia - country.

  The population of Cambodia is 14,241,640 (2008 estimate). Population growth per year is estimated at 1.8 percent, one of the highest rates in Asia. The rate of infantmortality is also high. The population density is 81 persons per sq km (209 per sq mi), with the densest concentrations on the heavily cultivated central plain. Themountainous regions of the country, where malaria is widespread, are thinly populated, as are the poorly watered northern provinces. During the late 1970s, under thebruta...

• New York (city) - geography.

  The Bronx is the fourth largest and the northernmost of the five boroughs, and the only one on the American mainland. Even so, it is surrounded by water on threesides: Long Island Sound on the east, the Harlem and East rivers on the south, and Hudson River on the west. Encompassing 109 sq km (42 sq mi), it had 1,332,650inhabitants in 2000. Largely residential, the Bronx includes dozens of vibrant neighborhoods. Fieldston is particularly elegant, with great stone houses set among spacious lawns a...

• Flood Control.

  When scientific research into the causes of floods showed that the construction of levees was insufficient as a method of control, the first steps were made to provide forreforestation and soil conservation. The Clarke-McNary Act of 1924, the Mississippi Flood Control Act of 1928, and the McSweeney-McNary Act of 1928 were all directedtoward that end. In 1935 the Soil Conservation Service was established by the Congress of the United States under an act declaring a policy of permanent provision f...

• Henry Morton Stanley.

  VI EVALUATION If Stanley was among the most ruthless and driven of Europe’s African explorers, he also was among the most accomplished. Much of what the Western world came toknow about Central Africa, including the drainage of its lakes and rivers, was derived from Stanley’s explorations. Moreover, he was one of the central figures in eventsleading to the Scramble for Africa. His call for the Christianizing of Africans and for the development of commerce with the interior echoed the call Livin...

• Henry Morton Stanley - explorer.

  VI EVALUATION If Stanley was among the most ruthless and driven of Europe’s African explorers, he also was among the most accomplished. Much of what the Western world came toknow about Central Africa, including the drainage of its lakes and rivers, was derived from Stanley’s explorations. Moreover, he was one of the central figures in eventsleading to the Scramble for Africa. His call for the Christianizing of Africans and for the development of commerce with the interior echoed the call Livin...

• Snorkeling.

  injury from animals is to be aware of diving conditions at a site, to dive with a buddy, and to leave the water promptly should a problem occur. Boaters can also pose a serious threat to snorkelers. If not near a boat or a visible dive flag, snorkelers can be virtually invisible to boaters and can be run over.Another common danger in snorkeling is fatigue, which can lead to drowning. V WORKING UNDERWATER Most underwater work is accomplished by scuba divers because they can remain underwater at...

• Alberta - Geography.

  C Climate Except for the mountain areas, summers throughout the province are quite warm. Winters are long and extremely cold. In July, average daily temperatures range fromabout 16°C (about 60°F) along the northern boundary to about 21°C (about 70°F) in the south. In the extreme southeastern section of the province, temperatures of43°C (110°F) have been recorded. In January, average daily temperatures range from about -14°C (about 6°F) at Grande Prairie to about -9°C (about 16°F) atCalgary. Tem...

• Alberta - Canadian History.

  C Climate Except for the mountain areas, summers throughout the province are quite warm. Winters are long and extremely cold. In July, average daily temperatures range fromabout 16°C (about 60°F) along the northern boundary to about 21°C (about 70°F) in the south. In the extreme southeastern section of the province, temperatures of43°C (110°F) have been recorded. In January, average daily temperatures range from about -14°C (about 6°F) at Grande Prairie to about -9°C (about 16°F) atCalgary. Tem...

• Duck - biology.

  from water. When ducks feed they push their tongue against the top of their mouth to squeeze water through the lamellae, leaving the food behind. Mergansers arefish-eating ducks with slender bills that are notched on the edges like the blade of a saw. These saw-toothed beaks help the ducks catch and hold their slippery prey. VI COURTSHIP AND REPRODUCTION Ducks form pairs long enough to mate, but most species find new mates each year. In a few species, including buffleheads and whistling ducks,...

• Tennessee (state) - geography.

  The climate of Tennessee is characterized by hot summers, mild winters, and abundant rainfall. C1 Temperature Average July temperatures range from less than 21° C (70° F) in the Blue Ridge region to 27° C (80° F) at Nashville and Memphis. Maximum daytime temperatures insummer often rise above 35° C (95° F) in central and western Tennessee. Daytime temperatures in the mountains rarely rise above 32° C (90° F). Summer nights tendto be warm and muggy in central and western Tennessee, but temperatu...

• Tennessee (state) - USA History.

  The climate of Tennessee is characterized by hot summers, mild winters, and abundant rainfall. C1 Temperature Average July temperatures range from less than 21° C (70° F) in the Blue Ridge region to 27° C (80° F) at Nashville and Memphis. Maximum daytime temperatures insummer often rise above 35° C (95° F) in central and western Tennessee. Daytime temperatures in the mountains rarely rise above 32° C (90° F). Summer nights tendto be warm and muggy in central and western Tennessee, but temperatu...

• Togo - country.

  corn, millet, and sorghum. The leading export crops are coffee, cotton, groundnuts, and cacao. Livestock, chiefly sheep and goats, are raised on the northern plateau.Fish are caught in Togo’s rivers and in the Gulf of Guinea. B Mining and Manufacturing Togo is a leading producer of phosphates, which are by far the country’s most significant mineral product. In 2004, 400,000 metric tons of phosphate rock were mined.Industrial activity is limited but growing. The leading manufactures include ceme...

• Water - chemistry.

  flourides in drinking water has been found to reduce tooth decay. See Fluorine. Seawater contains, in addition to concentrated amounts of sodium chloride, or salt, many other soluble compounds, as the impure waters of rivers and streams areconstantly feeding the oceans. At the same time, pure water is continually lost by the process of evaporation, and as a result the proportion of the impurities that givethe oceans their saline character is increased. See Ocean and Oceanography. VII WATER...

• Gabon - country.

  government is engaged in preservation and reforestation programs. The fish catch in 2005 was 43,941 metric tons. C Mining Mining has developed rapidly since Gabon’s independence in 1960. Annual production of extremely high-grade manganese ore, from Moanda in the southeast, was1,090,000 metric tons in 2004. The rich deposits of iron ore located at Mekambo and Bélinga in the northeast have reserves estimated at more than 500 million metrictons. Exploitation of the iron ore has been hampered by th...

• Indiana - geography.

  Michigan in Michigan. There are about 1,000 small natural lakes in Indiana, chiefly in the northern part of the state. The largest is Lake Wawasee, which covers almost 13 sq km (5 sq mi). Inthe central part of the state there are several lakes that were created behind dams on a number of smaller streams. They include Monroe Lake, near Bloomington; Geistand Eagle Creek reservoirs, northeast and northwest of Indianapolis; and Mississinewa and Huntington reservoirs, north of Marion. C Climate Most...

• Indiana - USA History.

  Michigan in Michigan. There are about 1,000 small natural lakes in Indiana, chiefly in the northern part of the state. The largest is Lake Wawasee, which covers almost 13 sq km (5 sq mi). Inthe central part of the state there are several lakes that were created behind dams on a number of smaller streams. They include Monroe Lake, near Bloomington; Geistand Eagle Creek reservoirs, northeast and northwest of Indianapolis; and Mississinewa and Huntington reservoirs, north of Marion. C Climate Most...

• Lesotho - country.

  V GOVERNMENT Under the terms of the constitution of 1965, which was suspended in 1970, Lesotho was a constitutional monarchy with a bicameral legislature. After a coup in 1986,legislative and executive powers were vested in the king but actually exercised by a 6-member military council and a 20-member council of ministers. In 1993 Lesothoadopted a new constitution that redefined the role of the monarchy and altered the legislative branch of the government. The king, who is head of state, has no...

• Michigan - geography.

  The interior location of Michigan in the northern part of North America results in a continental climate, characterized by four definite seasons with moist, mild to hotsummers and snowy, cold winters. Winds off of Lakes Michigan and Superior in winter create heavy snow accumulations in nearby areas. The tempering effects of LakeMichigan account for the presence of the state’s famous fruit-growing belt along the lake’s shore. Since the water is colder than the land in spring, the westerly windspa...

• Michigan - USA History.

  The interior location of Michigan in the northern part of North America results in a continental climate, characterized by four definite seasons with moist, mild to hotsummers and snowy, cold winters. Winds off of Lakes Michigan and Superior in winter create heavy snow accumulations in nearby areas. The tempering effects of LakeMichigan account for the presence of the state’s famous fruit-growing belt along the lake’s shore. Since the water is colder than the land in spring, the westerly windspa...

• Native Americans of Middle and South America.

  A line that snakes across central Mexico near the Tropic of Cancer forms the northern boundary of Mesoamerica; north of this line rainfall sharply declines and theclimate is much drier. The ancient civilizations of Mesoamerica all arose and developed in the area between this line and the Guatemalan highlands far to the south. Richvolcanic soils are found throughout much of the region. A2 People and Languages Mesoamerica was a great melting pot, home to many peoples and interrelated cultures. In...