1. Volcanoes 2 Cyamaba Volcano, Ecuador

2. Learning Goals Learn about the role of plate tectonics in causing volcanoes and learn what causes eruptions to be gentle or highly explosive. Identify the main types of volcanoes: shield volcanoes, stratovolcanoes, and cinder cones. Learn about other forms of volcanic activity such as geysers, hot springs, hydrothermal vents, and geothermal energy.

3. Vocabulary Terms caldera cinder cone volcano crater geothermal energy hydrothermal vent lava magma magma chamber Ring of Fire rock cycle shield volcano stratovolcano vent

4. Volcanoes The eruption of Mount St. Helens in 1980 reduced the height of this mountain from 2,932 meters (9,677 feet) to 2,535 meters (8,364 feet). Early in the morning of May 18, 1980, an earthquake triggered a landslide that caused the bulge to eject magma, water, and gases.

6. Lava Tubes, Santa Cruz Island Galapagos, Ecuador

8. Lava Tubes, Isabella Island Galapagos, Ecuador

9. Volcanoes Solid rock melts and becomes magma under certain conditions that lower the melting point of the material. At subduction zones, water is the key for solid rock to melt and become magma.

10. Volcanoes Most volcanic activity is found at the edges of tectonic plates, namely at divergent and convergent plate boundaries, but does not occur at transform plate boundaries.

12. Volcanoes High viscosity lava is associated with stratovolcanoes (also called composite volcanoes). These volcanoes range in height from 500 to 10,000 meters high.

13. Cotapoxi Volcano Summit, Ecuador

14. Cotapoxi Volcano, Ecuador

15. Laguna Cuicocha, Ecuador

16. Crater of the Extinct Volcano Puluahua, Ecuador

17. Tungurahua Volcano, Ecuador

18. Volcanoes Low viscosity, fast- flowing lava is associated with shield volcanoes. Because this lava easily flows down hill, shield volcanoes are gently sloped and flattened.

19. Wolf Island, Galapagos, Ecuador

20. Bartolome Island and Pinnacle Rock, Ecuador

21. Sunken Crater Bartolome Island, Ecuador

22. Volcanoes Cinder cone volcanoes are steep stacks of loose pyroclasts (clumps and particles of lava). Cinder cones are rarely higher than 300 meters.

23. Birth of Paricutin Volcano, Mexico 1943

24. Paricutin Volcano, Mexico

26. Paricutin Volcano, Mexico 2000

27. Volcanoes Lava viscosity also determines how explosive an eruption will be. Explosive eruptions occur when the lava has a lot of water and dissolved gases. Gentle eruptions are associated with fast-flowing lava from oceanic crust.

28. Volcanoes Volcanoes also form when an oceanic plate slides under another oceanic plate.

29. Hydrothermal Vents Hydrothermal vents are deep sea, chimney-like structures that occur along midocean ridges.

30. Volcanoes Some gemstones are also associated with volcanic activity. For example, diamonds form at high temperatures deep underground when carbon crystallizes inside rocks called kimberlites.

31. Volcanoes Geothermal energy is the useful product of volcanic activity. When steam from magma collects below ground, it can be tapped just like water in a well. The pressurized steam can be used to generate electricity.

32. Volcanoes Volcanic activity results in the formation of two kinds of igneous rocks: — extrusive — intrusive A batholith is a large underground rock that formed when a mass of magma cooled underground.

33. Volcanoes Key Question: Why do some volcanoes erupt explosively?