Volcanoes and Plate Tectonics

1. Volcanoes and Plate Tectonics

3. Ring of Fire

4. What is a volcano? • a weak spot in the crust where molten material, or magma, comes to the surface

5. What is Magma? A molten mixture of rock-forming substances, gases, and water from the mantle.

6. When does magma become lava? • When magma reaches the surface.

7. What is the Ring of Fire? • a major volcanic belt formed by the many volcanoes that rim the Pacific Ocean.

8. Where do volcanoes come from? • along diverging plate boundaries such as mid-ocean ridges and along converging plate boundaries where subduction takes place.

9. Describe how volcanoes form along the mid-ocean ridge? • Along the rift valley, lava pours out of cracks in the ocean floor, gradually building new mountains.

10. True or false? • Volcanoes can form along diverging plate boundaries.

11. True or false? • Many volcanoes form near converging plate boundaries where oceanic crust returns to the mantle.

12. How does subduction at converging plate boundaries lead to the formation of volcanoes • When the older, denser plate sinks beneath a deep-ocean trench into the mantle, some of the rock above the subducting plate melts and forms magma. Because the magma is less dense than the surrounding rock, it rises toward the surface. Eventually, the magma breaks through the ocean floor, creating volcanoes. Volcanoes can also form where oceanic crust is subducted beneath continental crust.

13. Island arc? • Volcano boundaries where two oceanic plates collide to create a string of islands

14. Name of 6 major island arcs? • Japan, • New Zealand, • Indonesia, • the Philippines, • the Aleutians, • the Caribbean islands

15. What is a hot spot? • an area where material from within the mantle rises and the melts, forming magma

16. How did the Hawaiian Islands form?? • They formed over millions of years as the Pacific plate drifted over a hot spot.

17. How do volcanoes change Earth’s surface? • When lava that has erupted from a volcano cools, it forms solid rock. In this way, volcanoes add new rock to existing land and form new islands.

18. Why do so many of Earth’s volcanoes occur at plate boundaries? • At the boundaries where plates diverge (pull apart) or converge (push together), the crust is weak and fractured, allowing magma to reach Earth's surface

19. Explain how hot spots created the Hawaiian Islands. • Lava erupted from the hot spot and built a volcanic island. The Pacific plate is slowly moving over the hot spot, so it carried the island away from the spot. Another volcanic island formed at the hot spot and then was carried away. Over time, a chain of islands formed.

20. What is the difference between magma and lava? • Magma is molten, rock-forming material underground. Magma that reaches the surface is called lava.

21. Define volcano • a weak spot in Earth's crust where magma comes to the surface

22. Define Ring of Fire • a belt of many volcanoes that rim the Pacific Ocean

23. Define island arc • a chain of volcanic islands that forms at the boundary where two oceanic plates push together and one plate subducts under the other plate