ICSE • Class 6 • Social Science • Ch 12
Estimated Time: 45 Mins
Study Progress: In Progress
North America: Location, Relief and Drainage
North America is the third largest continent in the world, covering an area of approximately 24.7 million square kilometres—which represents about 16.5 percent of the total land area of the globe and nearly 4.8 percent of the Earth's total surface. In size, it is surpassed only by Asia and Africa. The continent lies entirely within the Northern Hemisphere latitudinally and within the Western Hemisphere longitudinally. It extends from about 7 degrees North latitude (in the Isthmus of Panama) to about 83 degrees North latitude (at Cape Columbia on Ellesmere Island in northern Canada), and from about 20 degrees West longitude (in eastern Greenland) to about 180 degrees West longitude (at Attu Island in the Aleutian Islands of Alaska). Because of its tremendous east-west breadth, the continent spans five standard time zones, with the 100 degrees West meridian passing through its approximate physical centre.
North America is bounded by three great oceans: the Arctic Ocean to the north, the Atlantic Ocean to the east, and the Pacific Ocean to the west. In the south-east, it is washed by the warm waters of the Gulf of Mexico and the Caribbean Sea. In the extreme north-west, the narrow Bering Strait—only about 85 kilometres wide—separates the North American mainland (Alaska, USA) from the Asian continent (Siberia, Russia) and connects the Arctic Ocean with the Bering Sea of the Pacific. In the extreme south, the continent tapers into the narrow Isthmus of Panama, which links North America to South America. In 1914, human engineering opened the world-famous Panama Canal across this narrow strip, creating an artificial maritime shortcut that links the Atlantic and Pacific oceans, saving ships a dangerous voyage of over 12,000 kilometres around the southern tip of South America at Cape Horn. The continent also includes numerous islands, the largest of which is Greenland—the largest island on Earth—politically an autonomous territory of Denmark.
Politically, North America comprises 23 sovereign nations and several dependent territories, broadly grouped into three major divisions: Anglo-America (Canada and the United States of America), Central America (the seven isthmian nations: Belize, Guatemala, Honduras, El Salvador, Nicaragua, Costa Rica, and Panama), and the Caribbean Islands or West Indies (including the Greater Antilles—Cuba, Jamaica, Haiti, the Dominican Republic, and Puerto Rico—the Lesser Antilles, and the Bahamas). Canada, with its capital at Ottawa, is the largest country in North America by area and the second largest in the world after Russia; the United States of America, with its capital at Washington, D.C., comprises 50 states (including Alaska in the north-west and Hawaii in the Pacific) and is the most populous and economically powerful nation on the continent; and Mexico, with its capital at Mexico City, is the largest Spanish-speaking nation in the world.
Relief: The Four Major Physical Divisions of North America.
Viewed in cross-section from west to east across the continent, North America displays a striking symmetry. It consists of four major physical divisions:
The Western Cordilleras (Pacific Mountain System): Occupying the entire western third of the continent, the Western Cordilleras are an immense system of parallel young fold mountain ranges, high intermontane plateaus, and fault-block basins stretching for nearly 6,500 kilometres from Alaska in the north down to Panama in the south. Formed during the Alpine-Tertiary period, they form part of the tectonically active 'Pacific Ring of Fire' and are prone to earthquakes and volcanic eruptions. The Cordilleras consist of three principal parallel belts: (a) The Eastern Range, crowned by the majestic Rocky Mountains (extending from Canada to New Mexico, USA), which act as the great 'Continental Divide' separating rivers flowing into the Pacific Ocean from those flowing into the Atlantic or Arctic oceans; (b) The Central and Western Ranges, including the Alaska Range—where North America's highest peak, Mount McKinley (officially renamed Denali, standing at 6,190 metres above sea level), is located—the Coast Mountains of British Columbia, the Cascade Range (famous for active volcanic peaks like Mount St. Helens and Mount Rainier), and the Sierra Nevada (a massive block mountain in California); and (c) The Sierra Madre Occidental and Sierra Madre Oriental in Mexico. Enclosed between these towering parallel ranges lie several famous Intermontane Plateaus: the Yukon/Alaska Plateau in the north, the Columbia-Snake Lava Plateau, the arid Great Basin (an area of inland drainage containing the Great Salt Lake and North America's lowest point, Death Valley, which plunges to 86 metres below sea level in California), the Colorado Plateau (where the Colorado River has carved the magnificent, mile-deep Grand Canyon), and the high Mexican Plateau.
The Canadian (Laurentian) Shield: Situated in northern and eastern Canada around Hudson Bay, the Canadian Shield is a vast, U-shaped or horse-shoe-shaped plateau-plain occupying nearly half of Canada's total land area. It represents the ancient geological nucleus of North America, composed of intensely hard Precambrian crystalline igneous and metamorphic rocks (granite and gneiss) that are more than two to three billion years old. During the Pleistocene Ice Age, massive continental ice sheets repeatedly scoured the surface of the Shield, stripping off its topsoil and scraping down ancient mountains into a low, undulating erosional plain (peneplain). As the ice sheets retreated, meltwater filled the scoured rock hollows and dammed valleys, creating thousands of freshwater lakes—including Great Bear Lake, Great Slave Lake, Lake Athabasca, Reindeer Lake, Lake Winnipeg, and the northern margins of the Great Lakes. The Canadian Shield is sparsely populated due to its harsh, sub-Arctic winter climate and thin rocky soils, but it is one of the world's richest storehouses of metallic minerals—yielding immense deposits of nickel (around Sudbury, Ontario), iron ore, gold, silver, copper, platinum, and uranium—and is blanketed by dense coniferous (Taiga) forests that supply Canada's thriving lumber and paper pulp industries.
The Appalachian Highlands (Eastern Highlands): Running parallel to the Atlantic Ocean along the eastern margin of the continent—from Newfoundland and the St. Lawrence Valley in Canada southwards to Alabama in the USA—the Appalachian Highlands are ancient Old Fold Mountains formed hundreds of millions of years ago during the Paleozoic era. Because they are vastly older than the Rockies, continuous weathering and erosion by wind, rain, rivers, and ice have worn down their once-towering peaks into low, rounded, heavily forested ridges with an average elevation between 1,000 and 1,800 metres. The highest peak in the Appalachians is Mount Mitchell in North Carolina, rising to 2,037 metres. The Appalachian system includes the Blue Ridge, the Allegheny Plateau, the Catskill Mountains, the Green Mountains, and the White Mountains. Along the eastern foot of the Appalachians lies the gently sloping Piedmont Plateau. The sharp boundary where the hard crystalline rocks of the Piedmont Plateau drop abruptly to the soft sedimentary rocks of the Atlantic Coastal Plain is called the Fall Line. Along this Fall Line, all east-flowing rivers plunge in steep rapids and waterfalls, which provided early settlers with abundant water power and later hydroelectric power to establish major industrial cities such as Philadelphia, Baltimore, Washington, D.C., Richmond, and Raleigh. The Appalachians are also world-famous for their rich seams of anthracite and bituminous coal, which fuelled the American Industrial Revolution.
The Great Central Plains (Central Lowlands): Occupying the vast interior between the Western Cordilleras in the west and the Appalachian Highlands and Canadian Shield in the east, the Great Central Plains stretch for about 6,000 kilometres from the Arctic Ocean in the north to the Gulf of Mexico in the south. This vast triangular lowland is divided into several sub-regions: (a) The northern sub-Arctic plains, drained by the Mackenzie River into the Arctic Ocean, characterized by swamps, permafrost, and coniferous forests; (b) The High Plains and the Prairies—a vast expanse of gently undulating, treeless temperate grasslands with fertile dark chernozem and prairie soils, famous as the 'Granary of the World' for enormous commercial wheat and corn cultivation and mechanized cattle ranching; (c) The Mississippi-Missouri Alluvial Basin, built by layers of fertile river-borne silt, supporting intensive farming of maize (corn), cotton, soybeans, rice, and sugarcane; and (d) The low, flat Gulf and Atlantic Coastal Plains, rich in petroleum and natural gas.
Drainage: The Rivers and Lakes of North America.
The drainage of North America is partitioned by two master watersheds: the Rocky Mountains (the Continental Divide) in the west and the Appalachian Highlands in the east. North America's rivers drain into four distinct ocean basins:
The Gulf of Mexico and Atlantic Drainage: Drained primarily by the Mississippi-Missouri-Ohio River system—the longest river system in North America and fourth longest in the world, stretching approximately 6,275 kilometres. Originating from Lake Itasca in Minnesota (Mississippi) and the Rocky Mountains in Montana (Missouri), the river flows southward across the Central Plains and empties into the Gulf of Mexico below New Orleans through a famous bird's-foot delta. Another major river draining into the Atlantic is the St. Lawrence River, which flows north-eastward out of Lake Ontario into the Gulf of St. Lawrence, forming the busiest commercial inland waterway on the continent. The Rio Grande flows along the international border between the USA and Mexico before emptying into the Gulf of Mexico.
The Pacific Drainage: Rivers rising on the western slopes of the Rockies and Coast Ranges are generally shorter and swifter. The Colorado River flows south-west across the arid Colorado Plateau, cutting the Grand Canyon and entering the Gulf of California; it is harnessed by major multi-purpose dams like the Hoover Dam. The Columbia River, joined by the Snake River, flows through the north-western USA into the Pacific Ocean, famous for huge hydroelectric installations like the Grand Coulee Dam and valuable salmon fisheries. In the far north-west, the Yukon River flows across the Yukon Territory and Alaska into the Bering Sea.
The Arctic and Hudson Bay Drainage: Drained in the north by the Mackenzie River—the longest river in Canada (4,241 km)—which originates from Great Slave Lake and flows northward into the Beaufort Sea of the Arctic Ocean. Into Hudson Bay drain the Nelson-Saskatchewan, Churchill, and Albany rivers, which flow through dense forests and are used for floating timber logs and generating hydroelectric power.
Inland Drainage (The Great Basin): Rivers in the Great Basin (such as the Humboldt River) do not reach any ocean; they evaporate in desert sands or empty into inland salt lakes like the Great Salt Lake in Utah.
The Lakes of North America and the St. Lawrence Seaway.
North America contains more freshwater lakes than all other continents combined. Centred on the border between Canada and the USA lie the Five Great Lakes, remembered by the acronym HOMES: Lake Huron, Lake Ontario, Lake Michigan, Lake Erie, and Lake Superior. Lake Superior is the largest of the five and the largest freshwater lake on Earth by surface area (about 82,100 sq. km). Lake Michigan is the only Great Lake that lies entirely within the borders of the United States. Water flows from Lake Superior into Lake Huron via the St. Mary's River (bypassed by the Soo Canals), into Lake Erie via the Detroit River, and then drops into Lake Ontario through the Niagara River. Between Lake Erie and Lake Ontario, the river plunges over a steep dolomite cliff to form the world-famous Niagara Falls, generating vast amounts of hydroelectric power. Ocean vessels bypass Niagara Falls through the Welland Ship Canal. Together with the St. Lawrence River, the Great Lakes form the St. Lawrence Seaway—a 3,700-kilometre inland maritime highway connecting the Atlantic Ocean with deep-inland industrial ports like Duluth, Chicago, Detroit, Cleveland, Toronto, and Montreal.
Case Study: Lumbering in Canada and the Life of Lumberjacks.
Canada possesses one of the world's largest belts of natural coniferous (Taiga or Boreal) forests, stretching from the Atlantic to the Pacific between 50 degrees North and 65 degrees North latitude. Pure stands of softwood species—such as white spruce, black spruce, balsam fir, Douglas fir, red pine, white pine, cedar, and larch—make commercial forestry and lumbering one of Canada's foremost economic sectors, placing Canada as the world's leading exporter of newsprint and wood pulp. Lumbering is predominantly a winter occupation because the flow of tree sap stops (making logs lighter and easier to saw), the frozen snow-covered ground allows heavy timber logs to be dragged effortlessly to riverbanks, and melting ice in spring provides free water transport downstream to sawmills and pulp factories. The workers who cut, trim, haul, and transport logs in the forest camps are called Lumberjacks. Their work is organized into four specialized stages: (1) The High-Rigger, who scales tall conifers with spiked boots and safety harness to lop off the crown branches and rig haulage pulleys, followed by Fellers who fell the tree using modern chainsaws with a loud shout of 'Timber!'; (2) Buckers and Limbers, who strip off branches and saw the tree trunk into standardized log lengths; (3) Skidders, who drag the logs out of the forest using tractors, winches, or cables and stack them onto frozen riverbeds; and (4) River Drivers (or Log Drivers), who guide the floating logs down rushing rivers during the spring thaw using spiked boots and long peavey poles to clear dangerous log-jams.
