Earthquakes and Volcanoes

1. Earthquakes and Volcanoes

2. Key Ideas • Where do most earthquakes occur? • How do scientists learn about earthquakes? • What is a volcano?

3. What are Earthquakes? • Most earthquakes occur at boundaries of tectonic plates.

4. What are Earthquakes? • As plates move, their edges experience stress. • Eventually, the stress becomes so great that it breaks rock along the fault line. • Energy is released as seismic waves.

5. What are Earthquakes? • The exact point inside Earth where an earthquake originates is the focus. • The point on the surface directly above the focus is the epicenter.

6. What are Earthquakes? • Energy released by an earthquake is measured as shock waves.

7. Types of Waves • Earthquakes generate three types of waves: • Longitudinal waves • moves fastest, • 1st wave • Aka – Primary wave or P-wave • Compression wave

8. Types of Waves • Earthquakes generate three types of waves: 2. Transverse Wave - slower than p-wave - 2nd wave - Aka – Secondary wave or S-wave - Doesn’t travel thru liquids - Transverse Wave

9. Types of Waves • Earthquakes generate three types of waves: 3. Surface Waves - slowest wave - 3rd wave - Aka – seismic wave or l wave - Moves only across Earth’s surface - Most destructive

10. Measuring Earthquakes • Scientists use seismographs to determine the epicenter of an earthquake.

11. Measuring Earthquakes • Geologists use earthquakes to study Earth’s interior.

12. Measuring Earthquakes • Scientists use two scales to measure the effects of earthquakes. • Richter Scale – measures magnitude • Mercalli Scale – measures intensity • http://earthquake.usgs.gov/earthquakes/recenteqsus/

13. Volcanoes • A volcano is any opening in the Earth’s crust through which magma has reached the Earth’s surface. • These openings are called vents.

14. Types of Volcanoes • There are three main types of volcanoes: 1. Shield Volcanoes 2. Composite Volcanoes 3. Cone Volcanoes

15. Shield Volcanoes • Volcano formed from a buildup of magma/lava rich in iron and magnesium. • Shield volcanoes are some of the largest volcanoes.

16. Shield Volcanoes • Example: Mauna Loa in Hawaii 13,000 ft. above sea level – 30,000 ft above sea floor

17. Composite Volcanoes • Composite volcanoes are made from alternating layers of ash, cinders, and lava. • Eruptions alternate between lava flows and explosive activity. • Typically thousands of meters high and much steeper than shield volcanoes.

18. Composite Volcanoes • Example: Mt. Fuji, Mt. Hood, Mt. Rainier, Mt. St. Helens

20. Cinder Cone Volcanoes • Cinder cone volcanoes are the smallest and most abundant volcanoes. • Usually active for a short period of time, then dormant.

21. Cinder Cone Volcanoes • Example: Paricutin, Mexico

22. Volcanoes • Most occur at convergent plate boundaries. • Around the Pacific Plate is known as Ring of Fire. • 75% of the active volcanoes in the world are located around Ring of Fire.

23. Ring of Fire

24. Volcanoes • Underwater volcanoes occur at divergent plate boundaries. • Example: Iceland (Mid Atlantic Ridge)

25. Volcanoes • Volcanoes also occur at hot spots. • Mantle plumes rise from deep within the mantle and erupt at hot spots at the surface. • Example: Hawaii • http://volcanoes.usgs.gov/ • http://www.history.com/shows/how-the-earth-was-made/videos/the-krakatoa-volcano#the-krakatoa-volcano

26. Questions • Where do most earthquakes occur? • What is the difference between the epicenter and focus of an earthquake? • Identify and describe the three type of volcanoes. • Why do surface waves cause the most damage in an earthquake? • Why might a sudden increase in the number of earthquakes around a volcano indicate a possible eruption?