1. Volcanoes

2. l Evidence that we live in an active planet l The gods of the underworld l Millions of people live near active volcanoes –The greatest geological hazard

4. Mount Saint Helens- after

5. Hazard

7. Future hazard l Population near big, recently active volcanoes –Seattle –Mexico City –Quito –Indonesia –Japan

10. Lava l Molten rock that flows on the surface l Basaltic Lava –low silica, –fluid, –low gas, –not explosive l Andesitic Lava –high silica –viscous –gas-rich –explosive

13. Types of volcanoes l 1. Shield Volcanoes –Hawaii, Iceland –Basaltic l 2. Stratovolcanoes (or composite) –Mt. Saint Helens, Pinatubo, etc –Andesitic –Explosive

15. Shield Volcanoes l Huge broad cones l Gentle slopes l Made from lava flows l Basaltic l Form at hotspots l Not very dangerous l Predictable

22. Stratovolcanoes (composite) l Andesitic lava l Rich in dissolved gases l Violent eruptions alternate with lava flows l Steep-sided cones l Very dangerous l Unpredictable

25. Pyroclastic Flows l Product of explosive eruptions l Hot ash shot up into the atmosphere l Ash column collapses l Pyroclastic flow can travel 60 mi/hr l Ash can fall 100’s of miles away l Ash may affect global climate

28. Mt. Saint Helens before

29. Phreatic (vapor) eruption

30. Bulge

31. Mt. St. Helens Pyroclastic Eruption

32. After the eruption

34. Lahars (mudflows)

35. l Very destructive l Kill as many people as the eruption itself l Loose ash forms mud avalanches l Glaciers on top of volcano melt l Rain

36. Inside a volcanoe

37. Pyroclastic eruption

39. Volcanic landscape: A Caldera (Crater Lake)

41. Crater lake formation (caldera) l 1. Early eruptions from composite cone l 2. Great eruption empties the magma chamber l 3. Summit collapses l 4. Caldera fills with water

44. Plate Tectonic Settings of Volcanism

45. Plate tectonic settings of volcanoes