Forces That Change the Land Chapter 3 Lesson 14 TCAP Coach

Objectives 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 Earth’s crust called? A. faults B. folds C. plates D. mountains

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

2. Where are earthquakes and 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 volcanoes MOST LIKELY to occur? A. where the edges of the plates meet

3. Where is the longest mountain range on Earth? A. in Asia B. in North America C. in South America D. under the oceans

3. Where is the longest mountain range on Earth? D. under the oceans

4. If Earth were represented by an apple, which part would BEST 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 apple, which part would BEST represent Earth’s crust? B. the skin of the apple