Lesson 2

1. What Causes Changes to Earth’s Landforms? Rocky Coast: These tall rocks along the Australian coast are sea stacks. They are all that is left of a rocky cliff that was pounded to pieces by ocean waves (page 238). Lesson 2

2. Page 240 • Layers of Earth • Every minute of every day, you are on Earth’s surface. If you could cut open Earth and look inside, you would find the 4 layers shown in the diagram below. Mantle Inner Core Outer Core Crust • Earth’s thin outer layer is the crust. The crust includes the land that makes up the continents as well as the land under the oceans. • The mantle is the rock layer below the crust. The upper parts of the mantle are so hot that the rock can flow. In some places the rock is melted to form magma. • At Earth’s center is the core. The core is made mostly of iron and nickel. The outer coreis liquid. The inner coreis solid; it is solid because there is so much pressure on it. • Earth’s crust & upper mantle are broken into large slabs of rock called plates. The plates move on a layer of the mantle that can flow like taffy.

3. Page 241 • You can’t see the movement of these plates. The plates move only a few centimeters per year. Over a long time, this movement leads to the formation of different landforms. • Plates move in several ways. Some move toward each other. When two land plates meet, the edges crush and fold as one is pushed down under the other, forming mountain chains. • Where a land plate and an ocean plate or two ocean plates meet, islands made of volcanic mountains can result. • Some plates travel away from each other. Large cracks can form where two plates are moving apart.

4. Page 242 • Volcanoes • On the morning of May 18, 1980, the volcano Mount St. Helens, in the state of Washington, erupted. The major eruption threw ash 12 miles into the air. Hot rock and gas from Mount St. Helens covered the land, filled in streams, and destroyed forests around the volcano. • A volcano is a mountain that forms as lava flows through a crack onto Earth’s surface.

5. Volcanoes • There are different types of volcanoes: • One type is composite volcanoes. They are made of layers of lava, rock, and ash. • Hawaii has shield volcanoes. These huge mountains erupt slowly, and lava flows steadily down their gently sloping sides. • Cinder conevolcanoes are small and have steep sides. They shoot chunks of rock into the air and down their slopes. Page 242

6. Pages 242-243 Earthquakes Movement between two plates can cause earthquakes. An earthquake is the shaking of Earth’s surface caused by movement of rock in the crust. A seismogram shows the movement of Earth’s surface during an earthquake. Most earthquakes occur along faults. A fault is a break in the crust, where rock moves. Sometimes this rock sticks. After some time, it may move forward suddenly. The movement sends out waves of energy that move through the crust. This energy causes shaking, rolling, and cracking in the crust and Earth’s surface.

7. Rivers • Rivers are found all over Earth. Although they aren’t as dramatic as volcanoes or earthquakes, rivers can cause big changes to Earth’s surface. • Rivers flow through valleys. The shape of a valley depends on the way the river runs through it. In steep areas, rivers move quickly. The rushing water cuts into the soil and rock. These valleys are narrow and V-shaped. Page 244 • As a river gets older, its valley becomes less steep. The floor of the river becomes more level. The valley walls become farther apart. As a result, older rivers often have wide valleys with flat floors. They flow through the valleys in wide curves. • As rivers flow, they carry soil and rock. As a river moves, deposition occurs. In deposition, rivers drop bits of rock and soil along the way. The slower a river moves, the more deposition occurs. River deposition builds landforms such as deltas and floodplains.

8. Glaciers In some places, snowfall is high and temperature is low. Sometimes more snow falls in winter than melts in summer. The snow piles up year after year. As it thickens, it turns to ice. If the mass of ice starts to move downhill, it becomes a glacier. A glacier is a large, moving mass of ice. Page 245 There are two main types of glaciers—alpine glaciers and ice sheets. Alpine glaciers flow down mountain valleys. The ice scrapes the floor and sides of the valley as it moves. The glaciers widens the valley, giving it a U shape. Fiords form where these valleys reach the coast. Ice sheets are huge glaciers that cover large areas, such as Antarctica and Greenland.

9. Wind and Waves • You have seen trees bend and move on a windy day. Wind can affect the way Earth’s surface looks. Wind lifts particles and carries them. • Wind slams sand into rocky surfaces. The wind blown sand makes pits and grooves in rock. Wind also carries sand and deposits it in dunes, as you learned in Lesson 1. • Waves break down rocky cliffs. As the cliffs crumble, they move farther inland. • Waves also change the shape of sandy coastlines. They move sand from some areas and deposit it in other places. The erosion and deposition of sand creates beaches, sand bars, and barrier islands along the shore. Page 246

10. Look back on page 241 Mountain chains form Islands made of volcanic mountains can form Large cracks can form

11. Match the clue on the left to the term on the right. This occurs when rivers drop bits of rocks and soils. They are made of layers of lava, rock, and ash. This causes shaking, rolling, and cracking in the crust and Earth’s surface. These are large moving blocks of ice. Volcanoes Earthquakes Deposition Glaciers