1. Volcanoes

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

4. Mount Saint Helens- after

5. Hazard

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

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

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

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

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

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

28. Mt. Saint Helens before

29. Phreatic (vapor) eruption

30. Bulge

31. Mt. St. HelensPyroclasticEruption

32. After the eruption

34. Lahars (mudflows)

35. Lahars (mudflows) • Very destructive • Kill as many people as the eruption itself • Loose ash forms mud avalanches • Glaciers on top of volcano melt • Rain

36. Inside a volcanoe

37. Pyroclastic eruption

39. Volcanic landscape: A Caldera (Crater Lake)

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

44. Plate Tectonic Settings of Volcanism

45. Plate tectonic settings of volcanoes