Physical Geography of the United States and Canada
Jasmin Lalonde, who comes from the Canadian province of Ontario, refers to her country's diverse landscape, a geographic characteristic shared by Canada's North American neighbor, the United States.Both nations are huge. Together, they cover more than 7 million square miles (18 million sq. km). Their continental land area extends from the Arctic Ocean in the north to the Gulf of Mexico and the Rio Grande in the south;and from the Pacific Ocean in the west to the Atlantic Ocean in the east.
The United States and Canada generally share the same landforms. Both nations have towering, snowcapped mountains in the west; fertile, rolling plains in the center; and low, smoothly formed mountains in the east.
Western Mountain Ranges
The Pacific Ocean forms the western border of both the United States and Canada. Paralleling the coastline are a series of mountain ranges that were formed by the collision of two tectonic plates millions of years ago. This mountain system includes the Alaska Range,the Coast Range, the Cascade Range, and the Sierra Nevada. Together, these mountains are called the Pacific Ranges.
Another western chain called the Rocky Mountains lies east of the Pacific Ranges. The massive, craggy Rocky Mountains stretch more than 3,000 miles (about 4,800 km) from northern Alaska to northern New Mexico.
Like the Pacific Ranges, the Rockies were formed by tectonic forces millions of years ago. Many peaks in the Rockies, especially those in the state of Colorado, rise more than12,000 feet (3,658 m).
The area that lies between the Pacific Ranges and the Rocky Mountains is known as the intermontane basins and plateaus. The northern and southern parts of this dry expanse are plateaus, or high, level surfaces. The Columbia Plateau, in the north, was created by lava seeping out of cracks in the earth. The southern plateau, the Colorado Plateau, is heavily eroded. This natural activity has produced unusual landforms, such as the Grand Canyon and various flat-topped natural elevations called mesas.
Between the Columbia and Colorado plateaus lies the Great Basin. This broad, low bowl includes the hottest and lowest place in the United States -- Death Valley.
Farther north, the distance between the Rockies and the Pacific Ranges narrows. As a result, Canada's Fraser Plateau and Nechako Plateau are smaller than the plateaus of the United States.
The area east of the Rockies marks the beginning of the Great Plains. The Great Plains is a broad, flat upland extending for about 400 miles (about 644 km) from the Rocky Mountains through the central parts of Canada and the United States. In Canada and parts of the United States, the Great Plains is sometimes called the Interior Plains or High Plains, because of the area's high elevation. This elevation reaches up to 6,000 feet (1,829 m).
The Great Plains area is flat and has no significant change in landforms. Its elevation, however, descends gradually to the east at a rate of about 10 feet per mile (about 2 m per km). In the United States, this lower elevation signals the beginning of another plains area, the Central Lowlands. In Canada, the Interior Plains area continues to the Canadian Shield.
Eastern Mountains and Lowlands
The Appalachian Mountains lie to the east of the plains. This mountain system is North America's second-longest mountain range. Its1,500-mile (2,400-km) length extends from the Canadian province of Quebec to Alabama in the United States. The Appalachians also are North America's oldest mountains, and erosion has worn them down and rounded their ancient peaks.
East and south of the Appalachians in the United States lie coastal lowlands. To the east, the Piedmont, a wide area of low, rolling hills, and the Atlantic Coastal Plain lead to the Atlantic Ocean. To the south, the Gulf Coastal Plain fans out and extends westward into Texas. In Canada, the Canadian Shield is bordered by lowlands around Hudson Bay.
The United States and Canada have an abundance of water systems. Large rivers and lakes supply fresh water for metropolitan and rural areas in both nations.
Because rivers flow downhill, the pattern of landforms determines the direction in which water systems flow. A continental divide is a line that separates rivers that flow toward opposite ends of a continent. In North America, a high ridge of the Rockies known as the Continental Divide, or the Great Divide, separates the waters flowing west to the Pacific Ocean from those flowing east toward the Mississippi River and Atlantic Ocean. In Canada, the Continental Divide joins another divide known as the Height of Land, which separates the waters flowing into the Arctic Ocean.
Rivers in the United States whose headwaters, or water sources, are found in the Rocky Mountains include the Colorado River, which flows toward the west. The headwaters of the Rio Grande, the MacKenzie River, and the Missouri River are also in the Rockies. Each of these rivers has many tributaries, or brooks, rivers, and streams that feed their waters into one river.
The Mississippi is the largest river in the United States and Canada in both water volume and drainage area. It runs 2,340 miles(3,765 km) from its source near the border of the United States and Canada to its outlet in the Gulf of Mexico.
The United States and Canada also include many lakes formed as a result of the Ice Age. As the great frozen ice sheets advanced and retreated, the land over which they moved changed. As the ice moved relentlessly south, it formed dams on river systems and forced the waters to follow the glaciers' boundaries. It was this action that established the courses of the Missouri and Ohio rivers.
Some of this water blocked by glacial dams became lakes. In northern Canada, two major lakes, Great Bear Lake and Great Slave Lake, were formed in this way. They mark the ancient boundary of the glaciers.
As the glaciers moved over the land, they also gouged out and scoured hollows in the rocks they passed. As the glaciers receded, these hollows filled with water. The Great Lakes are examples of glacial lakes.
The Great Lakes -- Lake Superior, Lake Huron, Lake Erie, Lake Ontario, and Lake Michigan connect with one another and with the St. Lawrence River, whose mouth opens to the Atlantic Ocean. Glacial lakes, too numerous to count, also dot the Canadian Shield.
The United States and Canada have many important natural resources. The rivers and lakes of both nations supply plentiful amounts of freshwater. The waters of the shallow continental shelf along the Atlantic Ocean and the Gulf of Mexico teem with fish and shellfish as do the waters along the Pacific coastline. The major freshwater fisheries of the United States include the inland waters of the southern states and the Great Lakes. Fisheries are places for catching fish and other sea animals. The Great Lakes are the center of the freshwater fishing industry in Canada.
Mineral resources of the United States and Canada include gold, silver, nickel, iron, copper, uranium, and zinc. The Rocky Mountains contain a great wealth of gold, silver, and copper. Parts of the Canadian Shield have deposits of iron and nickel. Canadian officials estimate that the mostly unexplored northern areas of Canada may hold as much as 40 percent of the country's mineral riches. Important energy resources, such as oil, natural gas, and coal, are found throughout both nations. Rich coal deposits are found in the Appalachian Mountains and in the central and western parts of the United States and Canada.
Timber reserves include the huge forests that cover about one-third of each nation. More than 1,000 animal species thrive in these woodland areas.
Parts of the United States and Canada have excellent conditions for agriculture. The Great Plains and the Central Lowlands in the United States have some of the world's most fertile soil. Fertile farmlands also cover the vast Interior Plains of Canada.
The Climate and Vegetation
The locations and vast sizes of landforms in the United States and Canada influence the climate regions and vegetation in these nations. Many types of climate regions can be found in the United States and Canada.
In the United States and Canada, most of the earth's climate types are represented. Even a tropical rain forest climate can he found 2,400 miles (3,862 km) away from the United States mainland, on the islands of Hawaii.
Winds, ocean currents, and protective mountains along the Pacific coast help create a marine west coast climate from northern California through British Columbia to the southern border of Alaska.
As they blow eastward, the Pacific winds encounter the Pacific Ranges. As the winds are forced over the mountains, the air cools and moisture is released. This means that the west coast enjoys tremendous rainfall, and some parts of the area receive more than 100 inches (254 cm) of rain each year.
The Pacific Ranges also create a rain shadow, which limits the amount of rainfall east of the mountains. This place of plateaus and basins, bordered in the east by the Rocky Mountains, is known for its hot, dry air. The only deserts in the northern part of North America are found here. These deserts include the Great Salt Lake Desert, the Blackrock Desert, and Death Valley.
The higher parts of the Rocky Mountains and Pacific Ranges have highland climates. Even in Hawaii, with its tropical rain forest climate, some mountains have snowy peaks.
Large parts of Canada and Alaska lie in a subarctic climate zone with very cold winters. Two-thirds of Canada has January temperatures that average below 0F (-18C). Winter temperatures of -70F (-57C) have been recorded in some places. A persistent high pressure cell in this area spawns the cold winds that chill much of the central United States during the winter.
Farther north, lands across the Arctic coastlines lie in a tundra climate zone. These areas experience bitter winters and cool summers. This vast expanse of land is still a wilderness, inhabited by few people.
The Great Plains are far from oceans or other large bodies of water that moderate climate. Although western mountains block moisture-bearing Pacific winds, the Great Plains are not completely dry because moisture travels with winds that blow north along the Rockies from the Gulf of Mexico and south from the Arctic region. The region is classified as a humid continental climate region with bitter winters and hot summers.
The humid continental climate region continues east to the Atlantic. Most of the southern states, however, are in a humid subtropical climate region. Only the tip of Florida is far enough south to have a tropical savanna climate.
Seasonal Weather Conditions
Canada and the United States are affected by seasonal weather conditions. In winter, much of northern North America experiences blizzards. Blizzards are snowstorms with winds in excess of 35 miles (56 km) per hour, temperatures below freezing, and visibility of less than 500 feet (152 m) for 3 hours or more.
Summer tornadoes, swirling columns of air whose winds can reach 300 miles (483 km) per hour, plague the Great Plains and the eastern portion of the United States. During summer and autumn, hurricanes -- ocean storms hundreds of miles wide with winds of 74 miles (119 km) per hour or more -- threaten the Atlantic and Gulf of Mexico coastlines. Typhoons, or Pacific hurricanes, threaten Hawaii and other Pacific islands each year.
Some seasonal weather conditions are improvements over the normal patterns for a climate zone. For example, a warm wind called the chinook blows down the slopes of the Rockies in winter and early spring. This wind melts the snow at the base of the mountains, exposing grass for grazing cattle.
Before the arrival of settlers, almost half of present-day United States and Canada -- an estimated 3 million square miles (7,770,000 sq. km) was covered with forests. Over the past 2 centuries, humans, however, have permanently cleared over one-half million square miles (1,295,000 sq. km) of original forestland.
Despite human pressures on the land's resources, a vast forest area still spans subarctic Canada. Forests also cover the sides of the western mountain ranges until they reach the timberline, or the elevation above which trees cannot grow.
The Great Plains of the United States and Canada were once a prairie region, a treeless expanse of grasses whose tangled roots formed dense layers of vegetation called sod. Settlers, however, soon populated the plains, broke up the sod, and used it to build homes. These changes led to dust bowl conditions in the1930s. Since then, scientific farming methods have improved conditions on the Great Plains, and the region now supplies most of North America's wheat.