18.3 Volcanoes

1. 18.3 Volcanoes

2. When magma reaches Earth’s surface it is called lava.

3. Objectives • Compare and contrast shield, cinder-cone, and composite volcanoes. • Contrast the volcanism that occurs at plate boundaries. • Explain the relationship between volcanism and hot spots. • Describe the major parts of a volcano. Vocabulary • cinder-cone volcano • composite volcano • tephra • pyroclastic flow • hot spot • vent • crater • caldera • shield volcano

4. Tephra are rock fragments thrown into the air during a volcanic eruption. • A crater is a bowl-shaped depression at the top of a volcano that is connected to the magma chamber by a vent. • A vent is where lava erupts through an opening in the crust.

5. Calderas • Calderas are large depressions that can form when the summit or the side of a volcano collapses into the magma chamber.

6. Volcanoes Three main types: Shield Composite Cinder Cone

7. Shield • Very fluid lava- has Iron (Fe) and Magnesium (Mg). • Lava flows great distances • Mild eruptions • Gentle sloping • Some of the largest volcanoes in the world

9. Shield Volcano Mauna Loa - Hawaii

10. Composite • Made up of alternating layers of ash, cinders and lava • Lava rich in silica (Si) • Lava thick • Eruptions can be explosive • Steep slopes

11. Composite Mt Fuji Japan

12. Cinder cone • Smallest volcano type • Most abundant type • Lots of gas trapped in magma • Very explosive eruptions • Active for only a short time • Has bowl shaped crater in the center

13. Cinder Cones

15. Crater Lake

16. Lava Flow

17. Where do volcanoes occur? • 80% found at convergent boundaries. • 15% found at divergent boundaries. • 5% found far from plate boundaries.

18. Where do volcanoes occur? Mediterranean Belt. Pacific Ring of Fire.

19. Ring of Fire

20. Hot Spots • Hot spots are unusually hot regions of Earth’s mantle where high-temperature plumes of mantle material rise toward the surface. • A plume does not move laterally, which results in a trail of progressively older volcanoes that formed as a plate moved over a hot spot.

21. Hot Spot Plumes

24. A pyroclastic flow is a cloud of volcanic gas, dust, and other tephra traveling at speeds of nearly 200 km/h. The center of a pyroclastic flow can exceed 700°C. Pyroclastic Flows Mt. Saint Hellens Sakura-jima Soufriere Hills

25. Pinatubo Ash Deposit

26. Pyroclastic deposits • Over 100 pyroclastic fall deposits in Oshima on the Izu Islands

27. Section Assessment 1. Match the following terms with their definitions. ___ vent ___ crater ___ tephra ___ pyroclastic flow ___ caldera A. an opening in the crust from which lava flows B.depression caused by a collapsed magma chamber C.a bowl-shaped depression around an opening in the crust D. volcanic materials that are thrown into the air during a volcanic eruption E.a cloud of rapidly moving, extremely hot volcanic material A C D E B

28. Section Assessment 2. How can chains of volcanoes that form over a hot spot track plate movement? The hot spot is in a fixed location. All of the volcanoes in the chain were over the hot spot when they formed. The volcanoes’ movement and the direction of the chain’s alignment indicates the movement of the plate.

29. Section Assessment 3. Identify whether the following statements are true or false. ______ Many cinder-cone volcanoes are less than 500 m high. ______ Volcanism is more common along divergent boundaries as compared to convergent boundaries. ______ The Mediterranean Belt is also known as the “Ring of Fire”. ______ It can be 700ºC in the center of a pyroclastic flow. true false false true

30. If Yellowstone Erupted

33. Miscellaneous Info • Underwater volcano is called a seamount- they look a lot like composite volcanoes. • Most volcanoes occur at plate boundaries- convergent plate boundaries. • Volcanoes can occur in the middle of tectonic plates- these are called hotspots. Ex. Hawaiian Islands