Physical Geography

North AmericaNorth America is the third largest continent. Only Asia and Africa are larger.
Land

North America has a wide diversity of landforms, represented by six distinct regions and many subregions. There are three lowland regions (the Coastal Plain, the canadian Shield, and the Interior Plains) and three highland regions (the Appalachian Highlands, the North American Cordillera, and the Antillean System).

The Coastal Plain extends along the eastern coast from Mexico to Cape Cod. It continues offshore as the continental shelf, emerging southeast of Florida to form the Bahama Islands. The mainland portion of the Coastal Plain is narrow in the northeast but reaches a width of more than 400 miles (640 km) in the lower Mississippi River Valley. The low, generally flat plain rises slightly as it extends inland, where it is bordered by higher land for most of its length.

The Appalachian Highlands lie west of the Coastal Plain, reaching from Alabama northeastward to the island of Newfoundland. The region is a series of long, parallel mountain ridges lying between narrow plateaus on the east and west. These low, worn-down mountains reach their greatest height, 6,684 feet (2,037 m) above sea level, at Mount Mitchell, in North Carolina. Elevation decreases in the southern and northern mountains.

The Canadian Shield (or Laurentian Plateau) covers Greenland and much of central and northern Canada and extends into the United States in the Superior Uplands and the Adirondack Mountains. It is composed of hard crystalline rock scoured by glaciers that left hundreds of lakes. The plateau averages about 1,000 feet (300 m) above sea level, decreasing slightly westward and southward.

The Interior Plains region is a vast, comparatively level expanse occupying a large part of the continent's interior. It lies between the Appalachian Highlands, the Canadian Shield, and the Rocky Mountains, and merges with the Coastal Plain to the south. There are two major subregions, distinguished chiefly by their elevation. To the east are the Central Lowlands, which average about 600 feet (180 m) above sea level. The second subregion is the Great Plains, in the west. This relatively flat grassland ascends gradually to a maximum of 6,000 feet (1,800 m) at its western edge, the Rocky Mountains.

Two small highland areas are often included within the Interior Plains—the Black Hills of South Dakota and the Central Uplands (Ozark and Ouachita plateaus).

The North American Cordillera covers much of the western third of the continent. It is a complex highland region stretching from Alaska to southern Mexico and containing high mountains and broad plateaus. Its most prominent features are two great mountain systems—the Rocky Mountains and the ranges near the Pacific coast. The Rockies reach their highest elevations—more than 14,400 feet (4,390 m)—in Colorado, and gradually descend to the north and south. The Pacific mountains, which in some places are more rugged than the Rockies, have the continent's highest peaks. Mount McKinley, in Alaska, stands 20,320 feet (6,194 m) above sea level—the highest point in North America.

Between these two extensive systems are plateaus, basins, and scattered mountain ranges. This pattern continues southward, where Mexico's Central Plateau is rimmed by the Sierra Madres on the east and west. A belt of volcanic mountains south of Mexico City contains Mexico's highest peaks.

The Antillean System adjoins the North American Cordillera on the south, trending east and southeast from southern Mexico through Central America and the islands of the Antilles. The western peaks of Central America are generally the highest in the region, and include active volcanoes. The maximum elevation is 12,533 feet (3,820 m) in Costa Rica's Chirripó. Narrow coastal plains, formed mainly by deposits of mountain streams, fringe the mountains in many areas.

Water

The large size of the continent makes possible long rivers, and two of the longest in the world—the Mississippi and Mackenzie systems—flow across the continent. Two of the Mississippi's tributaries—the Ohio and the Missouri—are themselves major rivers. Shorter rivers, especially near the east and west coasts of the United States, are frequently used for navigation and for generating electric power. In Central America, rivers are little used because they are short and have swift currents.

Most of the continent's lakes are in the glaciated areas in the north. Though most of the lakes are small, eight of the world's largest are in this area. These eight are the Great Lakes and three Canadian lakes—Great Bear, Great Slave, and Winnipeg. There are few lakes in the dry southwest, and those that exist there (such as Great Salt Lake) are slowly decreasing in size because of evaporation. The only large lakes in Central America are Lakes Nicaragua and Managua.