1. Volcanoes Ch 22.6 Page 690

2. A. A volcano is a mountain that forms when magma reaches the surface B. Examples: Mount St. Helens, Kilauea

3. C. Formation of a Volcano Page 691 1. Under certain conditions, small amounts of mantle rock can melt, forming liquid magma. The magma rises upward through the crust, erupting at the surface of a volcano

4. 2. How a Volcano Erupts- magma is under pressure and contains dissolved gases. The volcano erupts when the gases bubble out through a crust, propelling magma to the surface

5. 3. Structure of a Volcano

6. a. Magma collects in a magma chamber b. Magma rises to the surface through a narrow, vertical chamber called a pipe

7. c. An opening in the ground where magma escapes to the surface is called a vent

8. d. Top of a central vent is a bowl- shaped crater pit called the crater e. If the shell collapses inward, it creates a huge depression, called a caldera

9. D. Quiet and Explosive Eruptions Page 692 1. Volcanoes erupt explosively or quietly, depending on the characteristics of the magma

10. 2. Three main factors determine the viscosity (resistance to flow) of magma

11. a.Temperature- higher temps, lower the viscosity so it flows easily b. Water content- high water content also helps it flow easily c. Silica content- high silica content also has high viscosity therefore does not flow easy

12. 3. Quiet Eruptions a. Very hot, low-silica b.Lava flow travels for great distance c.Mt. Kilauea

13. 4. Explosive Eruptions a. High- silica magma b. Mt St Helens

14. E. Location and Types of Volcanoes Page 693 1. Most volcanoes occur along plate boundaries or at hot spots in the crust

15. 2.Ring of Fire- volcanoes formed along trenches in the Pacific Ocean 3.Hot spot is a region where hot rock extends from deep within the mantel to the surface

16. 4. Three major types of volcanoes

17. a.Shield volcano- a wide, flat volcano produced from quiet eruption of low-viscosity lava produces

18. b.Cinder cone- a small, steep sided volcano formed when an eruption is entirely ash and cinders

19. c. Composite volcano- a volcano that forms from explosive eruptions that produce a combination of lava and ash

20. F. Other Igneous Features Page 696 1. Igneous features formed by magma include batholiths, sills, dikes, and volcanic necks

21. 2.A batholith is the largest type of intrusive igneous rock mass

22. 3. If the crack is parallel to existing rock layers, the magma hardens into a structure called a sill

23. 4.If the crack cuts across rock layers, the hardened magma forms a dike

24. 5. When magma hardens in a volcano's pipe, a structure called a volcanic neck may form

25. Plate Boundaries

26. Volcano Song Raging Volcano video