1. VOLCANOES

2. A few volcano basics… Active – a volcano that has erupted recently (geologically speaking) Dormant – (sleeping) has erupted within the past few thousand years – will likely erupt again Extinct – hasn’t erupted in 10’s of thousands of years; unlikely to erupt again

3. Mt. Rainier - active

4. Mount Baker - dormant

5. Shiprock Peak – extinct volcano

6. magma: molten rock inside the Earth lava: magma that has emerged on the Earth’s surface

7. er magma lava

8. hot spot: area of volcanic activity independent of lithospheric plates ex. Hawaii

11. Different types of volcanoes are categorized based on the viscosity of the magma.

12. viscosity: a fluid’s resistance to flow high viscosity = high resistance to flow ex. honey is more viscous than water

13. Low viscosity magmas allow gases to escape easily (they are hotter!) In higher viscosity lavas, gas pressures build up and erupt explosively

14. Viscosity is determined by silica content and temperature.

15. The higher the silica content, the higher the viscosity. The hotter the magma, the less viscous it is.

16. TYPES OF VOLCANOES 1. Shield 2. Composite 3. Cinder cones

17. Shield Volcanoes - largest volcanoes (tallest when measured from the ocean floor) - shaped like a gentle arch or shield -basaltic lavas (low silica content)

19. - usually non-explosive eruptions - mainly lava flows - found in Hawaii (Mt. Kilauea) and Iceland

21. lava tubes: caves left behind after lava flows

23. Composite Volcanoes - coned shaped; sometimes called stratovolcanoes - lava contains mostly andesite or rhyolite (higher silica content) - more viscous

24. -combination of explosive activity (pyroclastic) and lava flows - responsible for most deaths - ex. Mount Saint Helens Mt. Pinatubo Mt. Fuji Mt. Vesuvius

25. Mount Saint Helens, Washington State

27. Mt. Saint Helens, after eruption

28. Mount Pinatubo, 1994

29. Mount Fuji, Japan

30. Mount Vesuvius / Ruins of Pompei

32. Cinder Cones - smaller volcanoes - form quickly -are active for a few years and then usually go dormant

33. Wizard Island

34. ex. Paracutin, Mexico - 1943, hole in ground - 2 weeks prior, small tremors - 1st day grew 10 m - By 5th day it was 100 m tall - After 2 yrs, it was 400 m tall - went quiet after 9 years

37. Ring of Fire Area of the world where volcanoes are common Here is what a volcano on the ring of fire looks like:

38. Features of Volcanoes crater - depression found at the top of a volcano; formed by the explosion of the upper portion of the cone

39. hot springs: water is heated by the hot rock and reaches Earth’s surface geyser: heating and circulation of water forms a pattern (RARE!) ex. Old Faithful

41. caldera: a giant crater that can be more than 12.5 miles in diameter - formed by rare, very violent eruptions - none have occurred in recorded history (they are 1000 times more violent than Mt. St. Helens!) - Yellowstone caldera was formed 600,000 years ago!

42. Crater Lake, OR

43. Long Valley, CA

44. Aniakchak, AK

45. Volcanic Hazards Primary Effects

46. Lava flows: eruption of magma at Earth’s surface Lava flows vary based on the composition of the magma. We are specifically going to look at basaltic lava flows.

50. pahoehoe: fast moving; low viscosity - smooth ropy texture when it hardens - move at a rate of up to 20 mph

54. aa: slow moving; higher viscosity - blocky texture when hardens - move at rates of a few meters per day -found further away from volcano

57. Pyroclastic Activity: explosive volcanism where tephra is physically blown into the atmosphere tephra: any material that is blown out of a volcano (mostly ash)

60. ash fall: huge quantities of rock, glass and gas are blown high into the air - kills vegetation - contaminate water - structural damage - jet engine “flame out” - respiratory irritation

62. lateral blast: explosions of gas and ash from the side of the volcano; destroys part of the mountain ex. Mt. St. Helens

63. Ash flow (nuee ardentes) - move very quickly - destroys everything in its path

65. Poisonous Gases - CO 2, carbon monoxide, sulfur dioxide, and hydrogen sulfide - can cause acid rain; contaminates water supply and vegetation

67. Secondary Effects lahar: debris flows and mudflows -volcanic debris becomes saturated with water -ex. Mt. Pinatubo, Philippines

69. Buildings buried after lahars at Pinatubo

70. Aerial View, Pinatubo Aftermath

71. Predicting Volcanoes 1. Monitoring of Seismic Activity- often the earliest sign 2. Thermal monitoring - measuring ground temperatures

73. 3. Topographic Monitoring - mountain may tilt and swell before an eruption 4. Volcanic Gas Emissions - changes in composition of gases may indicates rising of magma

74. 5. Geologic History - geologists map and date rocks around the area