Chapter 21.2

1. By the end of this section you should be able to… • Identify where in the world most earthquakes occur • Explain how scientists learn about earthquakes and the Earth’s interior • Identify different types of volcanoes, and main components of them Chapter 21.2 Earthquakes and Volcanoes

2. http://www.history.com/video.do?name=How_the_Earth_Was_Made&bcpid=9787674001&bclid=15202215001&bctid=15346376001http://www.history.com/video.do?name=How_the_Earth_Was_Made&bcpid=9787674001&bclid=15202215001&bctid=15346376001 To recap…

3. Importance of learning about earthquakes and volcanic eruptions? • http://www.history.com/video.do?name=science&bcpid=1681694258&bclid=1683773459&bctid=4251563001 • http://www.history.com/video.do?name=modernmarvels&bcpid=1766638695&bclid=1803311433&bctid=1601306752 • http://www.history.com/video.do?name=science&bcpid=1681694258&bclid=1683773459&bctid=4256662001

4. What are earthquakes? • As plates move their edges can experience stress • A sudden release of energy ensues as the rocks break • This energy is released as seismic waves

5. The exact place where an earthquake originates is known as the focus • These waves travel in all directions • The point on the surface directly above the focus is known as the epicenter • Damage at the epicenter is usually the greatest because it is closest to the focus

6. Energy from earthquakes is transferred by waves • Earthquakes generate 3 types of waves • Longitudinal waves move faster through rock than any other waves do and are the first waves to reach seismographs • Longitudinal waves are also referred to as primary waves (p waves)

7. Longitudinal waves travel by compressions in the earths crust • The stretching behind a compression is known as a rarefaction

8. The second type of wave is known as a transverse wave • These waves move more slowly than p-waves • Since they travel slower they are known as secondary waves or s-waves • The motion of these waves is similar to that of waves in shaking a rope

9. Both types of waves travel in all directions much like the light travels from a light bulb • However, the third type of wave only travels across the surface, therefore they are known as surface waves • Surface waves cause more destruction than both p and s waves

10. Seismologists detect and measure earthquakes • Seismographs document the power and time intervals between p waves, s waves, and surface waves • Three seismograph stations are needed to locate the epicenter of an earthquake • This process is known as triangulation

11. Geologists use seismographs to study the Earth’s interior • Since s waves do not reach the other side of earths core scientists believe that the outer core is liquid • Waves change speed and direction when they travel through different materials or media

12. We use the Richter scale to measure earthquakes • Each step on the Richter scale represents a 30-fold increase in the energy released So what is the difference in energy between an earthquake of 3.3 and 5.3? 30 x 30 = 900 times stronger

13. Damage caused by an earthquake depends on several factors 1. distance between populated epicenter, 2. the depth of the focus 3. type of soil and construction found in the area

14. Scientists are trying to predict earthquakes • Several factors have been studied • They range from watching animals for strange behavior to measuring changes in the Earth’s crust • Some people believe that Earthquakes emit low frequency vibrations that can cause nausea or a feeling of anxiety before they occur

15. http://dsc.discovery.com/videos/understanding-volcanoes-images-from-pompeii.htmlhttp://dsc.discovery.com/videos/understanding-volcanoes-images-from-pompeii.html http://dsc.discovery.com/videos/understanding-volcanoes-pele-goddess-of-fire.html Volcanoes • A volcano is any opening in the Earth’s crust through which magma has reached Earth’s surface • These openings are known as vents • A barrage of different things can come out of these vents. They range from molten rock, small rocks and mineral particles known as ash, as well as large boulders • Volcanoes generally have one large vent but can have several small ones

16. Shield volcanoes have mild eruptions • Magma rich in iron and magnesium is very fluid and forms less viscous lava flows, therefore they typically do not explode • These lava flows also create a nice gently sloped mountain

17. Composite volcanoes have trapped gas • The volcano itself is made of alternating layers of ash, cinders, and lava • Since gas is trapped in the magma eruptions alternate between explosive and lava flowing

18. Cinder cones are the most abundant volcanoes • Large amounts of gas are trapped in magma and violent eruptions occur • Cinder cone volcanoes however, tend to be active for a short time • Cinder cones are also found underwater but are known as seamounts

19. Most volcanoes occur at convergent plate boundaries • Volcanoes are common around the edge of the pacific ocean because of subduction of oceanic crust under less dense continental crust • Underwater volcanoes occur at divergent plates boundaries • As plates move apart magma rises to fill the gap • This magma crates the volcanic mountains that form the ridges around a central rift valley

20. Volcanoes also occur at hot spots • Some volcanoes occur in the middle of plates • Hot rock known as mantle plumes break through oceanic plates • As plates move, the plume does not • Therefore a chain of islands are left behind