Lesson 2 Reading Guide - KC

1. Earthquakes and Volcanoes • What causes earthquakes? • What causes volcanoes to form? • How do earthquakes and volcanoes change Earth’s surface? Lesson 2 Reading Guide - KC

2. Earthquakes and Volcanoes • lava flow • volcanic ash • caldera • earthquake • fault • mid-ocean ridge • hot spot Lesson 2 Reading Guide - Vocab

3. Earthquakes • Because tectonic plates move very slowly, most changes to Earth’s surface take a long time. • But some changes occur very quickly and violently. • An earthquake is the rupture and sudden movement of rocks along a break or a crack in Earth’s crust. Lesson 2-1

4. An earthquake can change Earth’s surface quickly and dramatically. Dr. Roger Hutchinson/NOAA Lesson 2-1

5. Earthquakes(cont.) • The surface along which the crust moves is called a fault. • When pieces of crust slide past each other, energy is released, causing the ground to shake. Photograph by N.J. Silberling, USGS Photo Library, Denver, CO Lesson 2-1

6. Earthquakes • Most earthquakes begin in the lithosphere within about 100 km of Earth’s surface. • The focus is the area beneath Earth’s surface where rock that is under stress breaks, triggering an earthquake. • The point on the surface directly above the focus is called the epicenter. Lesson 2-1

7. Earthquakes • Earthquakes release energy in the form of vibrations or waves. • Body waves move through the Earth's interior traveling much more quickly than surface waves. • Surface waves move over Earth's surface. Lesson 2-1

8. Earthquakes-Types of Body Waves • Primary or P waves are the first energy waves that arrive after an earthquake occurs. They travel through both solids and liquids in a push-pull, linear motion, similar to an earthworm. • Secondary or S waves are the second energy wave that travels through the interior of Earth. They can only travel through solids in an up and down motion. Lesson 2-1

9. Earthquakes-Types of Surface Waves • Love or L waves: originate at the epicenter of an earthquake and arrive after the secondary waves. They are responsible for the most damage • Rayleigh waves are a second type of surface wave that arrive at a location distant from the epicenter. They travel in a backwards elliptical motion. Lesson 2-1

10. Most earthquakes occur near plate boundaries, though some occur very far from plate boundaries. Lesson 2-1

11. Earthquakes(cont.) • Earthquakes can create new landforms such as mountains. • Compression and tension forces produce ridges and mountains as Earth’s crust moves vertically. Lesson 2-1

12. Earthquakes(cont.) • Liquefactionrefers to when extreme shaking causes ground that is made up of loose sediment to behave more like a liquid than a solid. • Earthquakes can trigger landslides, which bring rocks and soil from the tops of mountains into valleys. Lesson 2-1

13. Earthquakes(cont.) Earthquakes that happen underwater can cause tsunamis—huge ocean waves created by movement at a fault. Lesson 2-1

14. Volcanoes • Volcanoes are landforms that form when magma erupts onto Earth’s surface as lava. • Volcanoes can occur at divergent and convergent plate boundaries and at hot spots. • There are approximately 1,500 active volcanoes on Earth. Lesson 2-2

15. The mountains that form as lava from a volcano at a divergent boundary builds up and cools are called mid-ocean ridges. Lesson 2-2

16. At some convergent boundaries, one tectonic plate sinks, melts the mantle, and forms magma that erupts onto the plate that does not sink. Lesson 2-2

17. Volcanoes (cont.) • Hot spots are locations where volcanoes form far from plate boundaries. • When a hot spot is under oceanic crust, it will form islands such as the Hawaiian Islands. • When a hotspot is under continental crust, it will form a geyser like Old Faithful at Yellowstone National Park in Wyoming. Lesson 2-2

18. Volcanoes (cont.) • Because magma is hot, it is also less dense than the rock material around it. • Rising magma and great pressure caused by dissolved gases eventually erupt through cracks in Earth’s surface, creating a volcano. Lesson 2-3

19. Most of Earth’s largest volcanoes are located at convergent plate boundaries. Lesson 2-3

20. Volcanoes (cont.) • When melted mantle material erupts, it flows over Earth’s surface, creating long streams of molten rock called lava flows. • The lava eventually cools and solidifies, forming solid rock. Royalty-Free/CORBIS Lesson 2-4

21. Volcanoes (cont.) • At convergent plate boundaries, part of the continental crust can become mixed with magma from the mantle. • When this mixture of molten materials erupts, it does not flow as easily as lava made only of melted mantle. • Instead of forming lava flows, it often solidifies in the atmosphere, where it breaks into small pieces of lava called volcanic ash. Lesson 2-4

22. Volcanoes (cont.) • Eruptions that eject ash high into the atmosphere are called explosive eruptions. • Lava also can be produced during these eruptions. Lesson 2-4

23. Before a volcano erupts, magma builds up in the crust in a reservoir called a magma chamber. Lesson 2-5

24. Shield volcanoes form after basaltic lava flows have occurred over time. • Shield volcanoes tend to be large with gentle slopes, such as Mauna Loa in Hawaii. J.S. Griggs/U.S. Geological Survey Lesson 2-5

25. Composite volcanoes form as lava flows and ash layers deposited by explosive eruptions build up. • Composite volcanoes often have steep sides and a cone shape. PhotoLink/Getty Images Lesson 2-5

26. Sometimes the surface above the chamber collapses, creating a large depression in the center of the volcano called a caldera. P.W. Lipman, U.S. Geological Survey Lesson 2-5

27. Volcanic ash and gases from explosive eruptions can blow high into the atmosphere, blocking sunlight. • This can cause the temperature of the atmosphere near Earth’s surface to decrease. P.W. Lipman, U.S. Geological Survey Lesson 2-6

28. Earthquakes occur when movement along a fault occurs. Earthquakes occur mostly along plate boundaries. They can cause great damage. • Volcanoes form at two types of plate boundaries. Lava cools and builds up, forming volcanoes and other landforms. Lesson 2 - VS

29. Earthquakes and volcanoes change the surface by building mountains, covering land with lava, and shifting the surface along faults. Lesson 2 - VS

30. 27. Which happens when extreme shaking causes sediment to behave more like a liquid than a solid? A. compression B. eruption C. liquefaction D. tsunami Lesson 2 – LR1

31. 28. Which is a long stream of molten rock which eventually cools, solidifies, and builds up over time as flat layers? A. mid-ocean ridge B. lava flow C. fault D. caldera Lesson 2 – LR2

32. 29. Which type of volcano often has steep sides and is cone shaped? A. caldera B. composite C. mid-ocean D. shield Lesson 2 – LR3

33. Do you agree or disagree? 30. Earthquakes occur and volcanoes erupt only near plate boundaries. 31. Volcanoes erupt melted rock. Lesson 2 - Now