Physical Features of the United States Geography: Section 2

Turn to page 4 in your textbooks What landforms are shown? What landforms are shown? Mountains, coastlines, oceans, rivers, gulfs, plains, basins, and canyons. Mountains, coastlines, oceans, rivers, gulfs, plains, basins, and canyons.

Forces That Have Helped Shape U.S. Landforms Continental Drift- Scientists believe that the Earth’s continents were once a single land mass (or perhaps two), which began to break up and drift apart some 240 million years ago. Continental Drift- Scientists believe that the Earth’s continents were once a single land mass (or perhaps two), which began to break up and drift apart some 240 million years ago.

Volcanoes and Earthquakes Volcanoes and earthquakes occur frequently along boundaries between shifting continental plates. Volcanoes and earthquakes occur frequently along boundaries between shifting continental plates. These violent phenomena play a key role in shaping of the land. These violent phenomena play a key role in shaping of the land.

Volcanoes occur when hot gases and magma (molten, or melted, rock within the Earth) build up pressure and spew forth from underground as lava. Volcanoes occur when hot gases and magma (molten, or melted, rock within the Earth) build up pressure and spew forth from underground as lava. As volcanoes erupt again and again over many centuries, they can create cone-shaped mountains. As volcanoes erupt again and again over many centuries, they can create cone-shaped mountains.

Pressure beneath the Earth’s surface also causes earthquakes, which can topple buildings and rip up the landscape. Pressure beneath the Earth’s surface also causes earthquakes, which can topple buildings and rip up the landscape. Earthquakes

Glaciers Many landforms in the United States especially in Alaska, in mountainous areas, and near Canada have been shaped by moving masses of snow and ice. Many landforms in the United States especially in Alaska, in mountainous areas, and near Canada have been shaped by moving masses of snow and ice. These glaciers, common in polar regions, form where more snow falls in winter that can melt in summer. These glaciers, common in polar regions, form where more snow falls in winter that can melt in summer.

Iceberg

Glaciers spread out during periods called ice ages, when global temperatures dip sharply. Glaciers spread out during periods called ice ages, when global temperatures dip sharply. During the last ice age, some 20,000 years ago, a mile high mountain of ice stretched from west of what is now Chicago to New York City and south to the Ohio River valley. During the last ice age, some 20,000 years ago, a mile high mountain of ice stretched from west of what is now Chicago to New York City and south to the Ohio River valley.

Erosion The moving of rocks and soil by glaciers is one of many forms of erosion-the wearing away of land by wind, rain, or ice. The moving of rocks and soil by glaciers is one of many forms of erosion-the wearing away of land by wind, rain, or ice. The Appalachian Mountains of the eastern United States are relatively old and eroded mountains. The Appalachian Mountains of the eastern United States are relatively old and eroded mountains. That is why they are lower and less rugged than the younger Rocky Mountains of the West. That is why they are lower and less rugged than the younger Rocky Mountains of the West.

Mountain Ranges and Plateaus Mountains are perhaps the most easily identified landforms. Mountains are perhaps the most easily identified landforms. These elevated areas of peaks and crests rise high above the surrounding countryside. These elevated areas of peaks and crests rise high above the surrounding countryside.

Other elevated landforms, plateaus, are flat or gently rolling expanding at high attitudes. Other elevated landforms, plateaus, are flat or gently rolling expanding at high attitudes. Altitude measures the height of a landform above sea level or another surface, such as the ocean floor. Altitude measures the height of a landform above sea level or another surface, such as the ocean floor.

Interior and Coastal Lowlands Lowlands are valuable landforms because they are often flat or gently rolling and thus suitable for agriculture. Lowlands are valuable landforms because they are often flat or gently rolling and thus suitable for agriculture.

In landforms called basins, flowing water with no outlet collects to form lakes that become very salty as water continually evaporates. In landforms called basins, flowing water with no outlet collects to form lakes that become very salty as water continually evaporates. A plain is a large area of level or gently rolling land. A plain is a large area of level or gently rolling land.

Between the lowlands and the mountains lies the Piedmont (French for “foot” and mountain”). Between the lowlands and the mountains lies the Piedmont (French for “foot” and mountain”). As you travel up a river from the coast, you know you have reached the Piedmont when you encounter a series of rapids and waterfalls; water flowing from the mountains to the sea makes a sharp drop as the elevation of the land suddenly changes. As you travel up a river from the coast, you know you have reached the Piedmont when you encounter a series of rapids and waterfalls; water flowing from the mountains to the sea makes a sharp drop as the elevation of the land suddenly changes.

This boundary between the Piedmont and the coast plains is called the fall line. This boundary between the Piedmont and the coast plains is called the fall line.

Major water features Water is an important natural resource, and so are rivers and lakes (landforms defined by water). Water is an important natural resource, and so are rivers and lakes (landforms defined by water). Rivers and lakes are useful for transportation, food (fish, shellfish, edible plants such as seaweed), and the removal of wastes. Rivers and lakes are useful for transportation, food (fish, shellfish, edible plants such as seaweed), and the removal of wastes.

Great Lakes Together, the five Great Lakes make up the largest body of fresh water in the world. Together, the five Great Lakes make up the largest body of fresh water in the world. Lakes Michigan, Superior, Huron, Erie, and Ontario. Lakes Michigan, Superior, Huron, Erie, and Ontario.

St. Lawrence River The Great Lakes empty into the Atlantic Ocean through the St. Lawrence River, one of two great rivers that drain the U.S. interior. The Great Lakes empty into the Atlantic Ocean through the St. Lawrence River, one of two great rivers that drain the U.S. interior.

A tributary is a stream or river which flows into a mainstream (or parent) river, and which does not flow directly into a sea. A tributary is a stream or river which flows into a mainstream (or parent) river, and which does not flow directly into a sea.

Acquiring New Orleans as part of the Louisiana Purchase was considered important to the development of the Mississippi and Ohio River valleys because the city served as a port for American agricultural goods.

Extensive Ocean Coastlines Access to oceans is a great advantage for trade and travel, and 23 of the 50 United States benefit from ocean coastlines. Access to oceans is a great advantage for trade and travel, and 23 of the 50 United States benefit from ocean coastlines.

Hawaii: An Archipelago Hawaii is the only state completely surrounded by ocean waters. Hawaii is the only state completely surrounded by ocean waters. An archipelago, or chain of islands, was created over the centuries by volcanic activity. An archipelago, or chain of islands, was created over the centuries by volcanic activity.

Mineral and Energy Resources Associated with the U.S. landforms are a variety of mineral and energy resources. Associated with the U.S. landforms are a variety of mineral and energy resources. They were first tapped by early Native Americans, who learned to use them in their daily lives. They were first tapped by early Native Americans, who learned to use them in their daily lives. Today, such resources are crucial to the operation of the U.S. economy. Today, such resources are crucial to the operation of the U.S. economy.

True Minerals Most minerals lack inorganic matter by products of living organisms. Most minerals lack inorganic matter by products of living organisms. These minerals are solid substances occurring in nature, each with its own distinctive chemical composition. These minerals are solid substances occurring in nature, each with its own distinctive chemical composition. Since minerals do not replicate themselves as animals and plants do, they are called nonrenewable resources. Since minerals do not replicate themselves as animals and plants do, they are called nonrenewable resources.

Energy Resources Energy is vital in every aspect of modern life. Energy is vital in every aspect of modern life. The United States has a variety of resources that can be used to produce energy. The United States has a variety of resources that can be used to produce energy. Coal, petroleum, and natural gas are fossil fuels: They originated from a combination of ancient organisms and ancient minerals. Coal, petroleum, and natural gas are fossil fuels: They originated from a combination of ancient organisms and ancient minerals.

Alternative Energy Solar power- energy from the sun. Solar power- energy from the sun. Alcohol- produced from plants such as corn. Alcohol- produced from plants such as corn. Methane- economical substitute for natural gas. Created by allowing inorganic matter such as manure to rot which emits gases. Methane- economical substitute for natural gas. Created by allowing inorganic matter such as manure to rot which emits gases. Geothermal Energy- heat from within the earth. Geothermal Energy- heat from within the earth. Windmills- Used to generate electricity from the wind. Windmills- Used to generate electricity from the wind. Shale oil- fossil fuel obtained by heating and crushing oil-bearing rocks. Shale oil- fossil fuel obtained by heating and crushing oil-bearing rocks.

Windmills

Windmills

Many of these alternative sources of energy are renewable resources. Many of these alternative sources of energy are renewable resources. The United States also has many sites that are suited to producing hydroelectric power, which is generated when falling water turns turbines. The United States also has many sites that are suited to producing hydroelectric power, which is generated when falling water turns turbines.