Section 1 Volcanic Eruptions

1. Section1 Volcanic Eruptions Chapter F6 Bellringer Make a labeled drawing showing what happens when a volcano erupts. Then describe the photographs on pages 156 and 157 in your textbook. Why do the characteristics of volcanic eruptions vary? Illustrate your responses in your science journal.

2. Section1 Volcanic Eruptions Chapter F6 Objectives Describe the different types of volcanoes and how they affect Earth’s surface.

3. Agenda • Today we will: • Complete a do now. • Learn about volcanoes by teacher power point.

4. Vocabulary • shield volcano • cinder cone volcano • composite volcano

5. Section1 Volcanic Eruptions Chapter F6 Volcanic Eruptions • A volcano is a vent or fissure in the Earth’s surface through which molten rock and gases are expelled. • Molten rock is called magma. • Magma that flows onto the Earth’s surface is called lava.

6. Section1 Volcanic Eruptions Chapter F6 Nonexplosive Eruptions • Nonexplosive eruptionsare the most common type of volcanic eruptions. These eruptions produce relatively calm flows of lava in huge amounts. • Vast areas of the Earth’s surface, including much of the sea floor and the Northwestern United States, are covered with lava form nonexplosive eruptions.

7. Section1 Volcanic Eruptions Chapter F6 Explosive Eruptions • While explosive eruptionsare much rarer than non-explosive eruptions, the effects can be incredibly destructive. • During an explosive eruption, clouds of hot debris, ash, and gas rapidly shoot out from a volcano. • An explosive eruption can also blast millions of tons of lava and rock from a volcano, and can demolish and entire mountainside.

8. Section1 Volcanic Eruptions Chapter F6

9. Section 2Effects of Volcanic Eruptions Chapter F6 Volcanic Eruptions and Climate Change • During a large-scale volcanic eruption, enormous amounts of volcanic ash and gases are ejected into the upper atmosphere. • As volcanic ash and gases spread throughout the atmosphere, they can block enough sunlight to cause global temperature to drop. • Other effects of volcanic eruptions are shown in the following Visual Concepts presentation.

10. Section 2Effects of Volcanic Eruptions Chapter F6 Effects of Volcanoes on Earth Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

11. Section 2Effects of Volcanic Eruptions Chapter F6 Different Types of Volcanoes • Volcanic eruptions can cause profound changes in climate, but the changes to the Earth’s surface are more familiar. • Perhaps the best known of all volcanic landforms are the volcanoes themselves.

12. Section 2Effects of Volcanic Eruptions Chapter F6 Different Types of Volcanoes, continued • There are three basic types of volcanoes: • Shield Volcanoes • Cinder Cone Volcanoes • Composite Volcanoes

13. Section 2Effects of Volcanic Eruptions Chapter F6

14. Section 2Effects of Volcanic Eruptions Chapter F6 Different Types of Volcanoes, continued • Shield volcanoes are built of layers of lava that are released from repeated nonexplosive eruptions. The lava spreads out over a wide area, creating a volcano with gently sloping sides.

15. Section 2Effects of Volcanic Eruptions Chapter F6 Different Types of Volcanoes, continued • Cinder cone volcanoes are made of pyroclastic material usually produced from moderately explosive eruptions. The pyroclastic material forms steep slopes.

16. Section 2Effects of Volcanic Eruptions Chapter F6 Different Types of Volcanoes, continued • Composite volcanoes are formed from explosive eruptions of pyroclastic material, followed by quieter flows of lava. These formations, among the most common types of volcanoes, have broad bases and sides that get steeper toward the top.

17. Section 2Effects of Volcanic Eruptions Chapter F6 Other Types of Volcanic Landforms • In addition to volcanoes, there are other landforms produced by volcanic activity. • Craters are funnel-shaped pits near the top of the central vent of a volcano.

18. Section 2Effects of Volcanic Eruptions Chapter F6 Other Volcanic Landforms, continued • Calderas are large, semicircular depressions that form when the magma chamber below a volcano partially empties and causes the ground above to sink. • Calderas can appear similar to craters, but are many times larger.

19. Section 2Effects of Volcanic Eruptions Chapter F6

20. Section 2Effects of Volcanic Eruptions Chapter F6 Other Volcanic Landforms, continued • Lava Plateaus are wide, flat landforms that result form repeated nonexplosive eruptions of lava that spread of a large area. • The lava that formed lava plateaus usually erupted from long cracks, or rifts, in the crust over a period of millions of years.

21. Section 3Causes of Volcanic Eruptions Chapter F6

22. Section 3Causes of Volcanic Eruptions Chapter F6 When Tectonic Plates Separate • At a divergent boundary, tectonic plates move away from each other, forming a set of deep cracks called a rift zone between the plates. • Mantle rock rises to fill the gap opened by the separating tectonic plates. When mantle rock nears the surface, pressure decreases, which causes the mantle rock to melt and form magma.

23. Section 3Causes of Volcanic Eruptions Chapter F6

24. Section 3Causes of Volcanic Eruptions Chapter F6 When Tectonic Plates Separate, continued • Mid-Ocean Ridges Form at Divergent Boundaries Lava that flows from undersea rift zones produces volcanoes and mountain chains called mid-ocean ridges. • At these mid-ocean ridges, lava flows out and creates new crust. Most volcanic activity on Earth occurs at mid-ocean ridges.

25. Section 3Causes of Volcanic Eruptions Chapter F6 When Tectonic Plates Collide • Convergent boundaries are places where tectonic plates collide. • When an oceanic plate collides with a continental plate, the oceanic plate usually slides underneath the continental plate. This is a process called subduction.

26. Section 3Causes of Volcanic Eruptions Chapter F6 When Tectonic Plates Collide, continued • Subduction Produces Magma As descending oceanic crust scrapes past the continental crust, the temperature and pressure increase. • The following Visual Concepts presentation shows how subduction produces magma, and how that magma can rise to form a volcano.

27. Section 3Causes of Volcanic Eruptions Chapter F6 Volcano Formation at Convergent Boundaries Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

28. Section 3Causes of Volcanic Eruptions Chapter F6 Hot Spots, continued • A hot spot often produces a chain of volcanoes. One theory is that the mantle plume stays in the same spot while the tectonic plates move over it. • Other scientists think that hot spots are the result of cracks in the Earth’s crust. • The theory argues that hot-spot volcanoes occur in chains because they form along the cracks in the Earth’s crust.

29. Section 3Causes of Volcanic Eruptions Chapter F6 Predicting Volcanic Eruptions • Volcanoes are classified in three categories: • Active Volcanoes • Dormant Volcanoes • Extinct Volcanoes

30. Section 3Causes of Volcanic Eruptions Chapter F6 Active, Dormant, and Extinct Volcanoes Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

31. Homework • Handout.