Forces That Change the Forces That Change the LandLand

Chapter 3Chapter 3

Lesson 14Lesson 14

TCAP CoachTCAP Coach

ObjectivesObjectives

• Describe internal forces such as volcanoes, earthquakes, faulting, and plate movements that are responsible for the earth’s major geological features such as mountains, valleys, etc.

Forces That Change the LandForces That Change the Land

• Mountains, valleys, and rivers, and many other features cover Earth’s surface.

• Mountains form on Earth’s surface, and even on the bottom of the ocean.

• Long ago, Earth’s landforms, or surface features, were different than they are today.

Forces That Change the LandForces That Change the Land

• The features on Earth’s surface change slowly over time, but sometimes its features can also change rapidly.

• In this lesson, you will learn what causes these changes.

Earth’s CrustEarth’s Crust

• Earth is made up of different layers.• The outermost layer is called the crust. It is very

thin compared to Earth’s inner layers.• If you think of Earth as an egg, the crust is the

shell.• The crust includes the seven large landmasses

called continents.• It also includes the land under the ocean and it

is made up of solid rock.

Earth’s CrustEarth’s Crust

• The inside of Earth is very hot.

• Heat and pressure melt some of the rock under the crust.

• Heat and pressure also cause rocky materials inside Earth to move.

• These movements cause changes in the crust.

Earth’s CrustEarth’s Crust

• The crust is not all in one piece.• It is made up of giant pieces called plates.• The plates float on partly melted rock

underneath.• The plates can bump into each other, move

apart, or slide past each other.• The biggest changes in Earth’s crust happen at

places near where the edges of the plates meet.• These places are called plate boundaries.

Mountain BuildingMountain Building

• The highest mountains form when two plates bump into each other.

• The plates push against each other and this squeezes the land and pushes it upward.

• The layers of the rock form folds in the crust.• The tops of the folds become mountains.• Mountains that form this way are called folded

mountains.

Mountain BuildingMountain Building

• Examples of folded mountains include the Himalayas in Asia, the Andes in South America, the Alps in Europe, and the Rocky Mountains in North America.

• This diagram shows how folded mountains form.

Mountain BuildingMountain Building

• Sometimes movement of the plates causes a crack in Earth’s crust. This is called a fault.

• The land may slide up between two faults.• Such a movement builds mountains called

fault-block mountains.• In other places, the land may move down

between the two faults. This movement produces a landform called a rift valley.

Volcanoes and EarthquakesVolcanoes and Earthquakes

• Volcanoes can also form mountains.

• A volcano is an opening in Earth’s surface that lets melted rock, ash, and gases escape. The sudden release of these materials from a volcano is called and eruption.

• On the surface, the melted rock, called lava, cools and hardens.

Volcanoes and EarthquakesVolcanoes and Earthquakes

• It piles up around the opening.

• Later eruptions may repeat the process.

• Over time, the eruptions may build a mountain around the volcano.

• Mount Rainier in the state of Washington formed in this way.

Volcanoes and EarthquakesVolcanoes and Earthquakes

• Volcanoes also build up mountains from the ocean floor.

• When such mountains grow tall enough to rise above the ocean, they become volcanic islands. That is how the Hawaiian islands were formed.

Volcanoes and EarthquakesVolcanoes and Earthquakes

• Stress can build up in Earth’s crust as the plates push and pull.

• Then rock may break or move suddenly along a fault.

• This motion produces an earthquake, a shaking of the land.

• Earthquakes can change landforms by moving them up, down, or sideways.

Volcanoes and EarthquakesVolcanoes and Earthquakes

• Earthquakes and volcanoes happen most often near the boundaries of plates.

• Such boundaries exist along the western coast of the United States.

• That is why earthquakes often strike the states of California, Oregon, Washington, and Alaska. Volcanoes are found in those states as well.

Ocean BasinsOcean Basins

• An ocean basin is the bowl-shaped land under an ocean.

• Mountains form in ocean basins where melted rock breaks through the crust.

• This happens where underwater plates are moving apart.

• The process produces a long valley and a mountain range.

• The longest mountain range on Earth snakes through its oceans. It is about 80,000 km (49,711 miles) long.

1. What are the large pieces of 1. What are the large pieces of Earth’s crust called?Earth’s crust called?

• A. faults

• B. folds

• C. plates

• D. mountains

1. What are the large pieces of 1. What are the large pieces of Earth’s crust called?Earth’s crust called?

• C. plates

2. Where are earthquakes and 2. Where are earthquakes and volcanoes MOST LIKELY to occur?volcanoes MOST LIKELY to occur?

• A. where the edges of the plates meet

• B. where mountains grow

• C. under the sea

• D. in the middle of the continents

2. Where are earthquakes and 2. Where are earthquakes and volcanoes MOST LIKELY to occur?volcanoes MOST LIKELY to occur?

• A. where the edges of the plates meet

3. Where is the longest mountain 3. Where is the longest mountain range on Earth?range on Earth?

• A. in Asia

• B. in North America

• C. in South America

• D. under the oceans

3. Where is the longest mountain 3. Where is the longest mountain range on Earth?range on Earth?

• D. under the oceans

4. If Earth were represented by an 4. If Earth were represented by an apple, which part would BEST apple, which part would BEST

represent Earth’s crust?represent Earth’s crust?

• A. the core of the apple

• B. the skin of the apple

• C. the flesh of the apple

• D. the seeds of the apple

4. If Earth were represented by an 4. If Earth were represented by an apple, which part would BEST apple, which part would BEST

represent Earth’s crust?represent Earth’s crust?

• B. the skin of the apple