North America,

A brief treatment of North America follows. For full treatment, see MACROPAEDIA: North America.

For current history and for statistics on society and economy, see BRITANNICA BOOK OF THE YEAR.

Except where the relatively narrow Isthmus of Panama extends southeastward to connect with Colombia in South America, the continent, shaped like an inverted triangle, is completely surrounded by water. The Pacific Ocean extends the length of its western coast, the narrow Bering Strait separates it from Russia and Asia to the northwest, the Arctic Ocean and several of the continent's major islands lie to the north, the Atlantic Ocean lies to the east, and the Caribbean Sea and the Gulf of Mexico are situated in the southeast. The population in 1990 for the entire continent was estimated to be 424,523,000, or about one-twelfth of the world's population.

The land

The Cordilleras extend the length of the continent, from the Aleutian Islands in the northwest through Panama in the south and into South America, and occupy about one-third of the continent's total land area. A complex mountain system, the Cordilleras comprise two major branches: the Western Cordillera (or the coastal ranges) and the Eastern Cordillera. The coastal ranges contain some of the continent's highest mountains; its highest, Mount McKinley, rises to 20,320 feet (6,194 m) above sea level in Alaska. Stretches of the coastal ranges are geologically very active, dramatically so along an east-west extension located in southern Mexico and much of Central America. Almost no major city in this area has escaped severe earthquake damage, and most are sited near active volcanoes; among the most dramatic eruptions was that of El Chichón in southern Mexico in 1982.

The Rocky Mountains, joining the Mackenzie Mountains in the Yukon to the north and forming a chain southward with Mexico's Sierra Madre Oriental range and the nonvolcanic ranges of Central America, constitute the continent's Eastern Cordillera. Even though the Eastern Cordillera has no peaks as high as some of those in the coastal ranges, several exceed 14,000 feet (4,270 m). The eastern ranges form a drainage divide separating the Pacific drainage to the west from the watersheds of the Arctic to the north and those of the Atlantic and Caribbean to the east.

Interspersed within the North American Cordillera system are several plateaus, basins, troughs, and valleys. The large plateau region of the western United States and northern Mexico consists of the Columbia Plateau, the Colorado Plateau, the Basin and Range Province, and the Central Mexican Plateau. The region also contains an extensive interior drainage basin (the Great Basin) containing the Great Salt Lake, spectacular canyons cut by the Colorado River watershed, and the continent's major desert areas.

The eastern two-thirds of the continent is dominated by four major lowland regions: the Canadian Shield to the northeast; the Great Plains and the Interior Lowlands, extending westward and southward from the shield region; and the Coastal Plain, extending the length of much of the continent's eastern seaboard from New England in the United States through Mexico's Yucatán Peninsula. The bowl-shaped Canadian Shield, occupying the entire northeastern portion of the continent, is partially submerged at its centre, forming Hudson Bay. The southern and western boundaries of the shield are marked by the Great Lakes and smaller bodies of water; southward, the Laurentide Scarp drops precipitously by as much as 2,000 feet (610 m) along the length of the St. Lawrence River and the northern coasts of Lakes Huron and Superior; westward are a series of smaller lakes, dominated by the Great Bear Lake to the north. West of the lake systems lie the Great Plains, which extend south from the Arctic to the Rio Grande. Lying south of the Great Lakes are the Interior Lowlands, which extend eastward from the Great Plains to the Appalachian Mountains. The Great Plains, rising gradually from east to west, are terminated abruptly by the Rocky Mountains, which rise along the entire westernmost extent of the plains. The Interior Lowlands occupy the remaining low-lying terrain west of the Appalachian Mountains; this includes both the "Corn Belt" of the United States and the Ontario Lowlands of Canada, two of the most productive agricultural areas in the world.

The Coastal Plain, generally submerged along the eastern seaboard of the United States, is characterized by inundated river basins and extensive sand formations and rises gradually along the Piedmont Uplands to meet the Appalachian escarpment. The remaining plains include the Florida Peninsula and continue westward to meet the lower extensions of the Great Plains and the Interior Lowlands before turning southward along the entire eastern seaboard of Mexico. The Appalachians extend southwestward from Newfoundland in Canada to Alabama in the United States. The Caribbean Islands (Antilles Arc) make up the remainder of the continent's land area and essentially comprise partly submerged mountain chains that extend eastward from Central America and northward from South America.

The Mississippi River basin, including its major tributaries, the Missouri and Ohio rivers, has an area of about 1,250,000 square miles (3,250,000 square km), occupies more than one-eighth of North America's total area, and accounts for about one-fifth of the continent's total runoff. Three major rivers, the Mackenzie, the Yukon, and the Nelson, have outlets north of 55 N latitude and combine to drain an area larger than that of the Mississippi; their combined runoff is nearly equal to the Mississippi's. The inland waterways provided by the Mississippi and its tributaries, together with that of the Great Lakes and the St. Lawrence River, are unequaled in the world. Roughly following the perimeter of the Canadian Shield, a chain of lakes, including the Great Bear, Great Slave, and Winnipeg lakes to the west and the five Great Lakes to the south, contains an immense quantity of fresh water; their combined area, including Lake Superior's 31,700 square miles (the largest surface area of any freshwater lake), is nearly equal to the total land area of Germany. The Columbia and Colorado rivers in the western United States have been harnessed for irrigation and hydroelectric power. The Rio Grande forms part of the boundary between Mexico and the United States. Lakes Managua and Nicaragua in Central America, scarcely 100 feet (30 m) above sea level, are the lowest-lying lakes on the continent.

Between the extreme climatic conditions of the humid tropical regimes in Central America and the bitterly cold Arctic deserts, generally temperate climatic conditions prevail from Hudson Bay through much of Mexico. While average annual temperatures vary primarily with latitude and elevation, precipitation patterns generally are more critical in determining regional climatic variations. The wet regions, with more than 65 inches (1,600 mm) of average precipitation (though this is often seasonal), are located primarily along the northwestern Pacific coast, throughout much of Central America, and in the Dominican Republic among the Caribbean Islands. Extreme aridity (annual precipitation averaging less than 10 inches [250 mm] but often much less) is found in the western deserts stretching through the Great Basin region of the western and southwestern United States into northern Mexico (including Baja California) and in the extreme northern stretches of the continent, including most of the Arctic islands. Relatively humid regions (between 50 and 65 inches [1,300 and 1,600 mm] of annual precipitation) lie in the southeastern United States and in much of the Caribbean. The Interior Lowlands and much of the Canadian Shield receive between 20 and 50 inches (500 and 1,300 mm). The Great Plains and most of northern Canada receive between 10 and 20 inches; much of this falls as snow and varies from year to year. Frost-free periods range from about 90 to 120 days along much of the U.S.-Canadian frontier and from about 240 to 270 days along the Mexican-U.S. frontier. Throughout most of Mexico and the Florida Peninsula, frost occurs in intermittent years (and then for only brief periods).

Across the far northern reaches of Canada and Alaska is found a vast marshy region of tundra vegetation. To the south of this, one of the world's largest areas of coextensive forests--the North American boreal forest (taiga)--stretches across northern Canada from Newfoundland to Alaska. Other forested regions include the Pacific coniferous forest along the Pacific coast from California to Alaska, containing immense redwoods and firs; the largely coniferous Cordilleran forest in the montaine regions of western North America; a variety of mixed broadleaved and coniferous forests in the east-central and southeastern parts of the continent; and the tropical rain forests of southern Mexico and Central America. The Great Plains and western Interior Lowlands, once covered by vast grassland prairies, now consist largely of farms and rangeland. Cacti, sagebrush, and mesquite grasses are typical of the western desert regions, while mangrove swamps are found along much of the Gulf Coast from Mexico to the well-known Everglades of Florida.

North American wildlife includes huge herds of caribou and packs of timber wolves in the far north; elk, mountain goats, and grizzly bears in the Mackenzie and Rocky mountains; moose and beaver throughout much of the Canadian Shield; such reptiles as alligators and snakes in the southeastern United States; and a variety of species in the Central American rain forests, including parrots, monkeys, exotic reptiles and amphibians, and leopards. Bison, which once roamed in great numbers across the grasslands of the Great Plains, have been reduced to small herds in protected reserves. Fish abound in the continent's extensive bodies of fresh water; and bird populations, both resident and migratory, are enormous.

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