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THE ROCK CYCLE

THE ROCK CYCLE. VOLCANISM. I. Introduction. From: Roman god of fire, Vulcan. I. Introduction. From: Roman god of fire, Vulcan What is a volcano? A conical mountain formed around a vent where lava, pyroclastic materials, and gases are erupted. I. Introduction. B. Volcanic activity:

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THE ROCK CYCLE

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  1. THE ROCK CYCLE

  2. VOLCANISM

  3. I. Introduction From: Roman god of fire, Vulcan

  4. I. Introduction From: Roman god of fire, Vulcan • What is a volcano? A conical mountain formed around a vent where lava, pyroclastic materials, and gases are erupted.

  5. I. Introduction B. Volcanic activity: • Active • Dormant • Extinct

  6. B. Volcanic Activity 1. Active volcanoes • activity in the last few centuries Ex: Vesuvius, 79 A.D. (50 times in 2000 yr) Ex: Mt. St. Helens (1980)

  7. B. Volcanic Activity 2. Dormant volcanoes • “quiet” for the last hundred to thousands of years, but still have potential to erupt. Mt. Rainier

  8. B. Volcanic Activity 3. Extinct volcanoes • No eruption in historical times • No signs of erupting again

  9. Introduction C. Volcano Distribution • Most volcanoes occur in one of three areas: • Circum-Pacific (i.e. The Ring of Fire) • 60% • Mediterranean • 20% • Spreading centers • 10 – 15%

  10. Volcano Distribution

  11. II. Volcanic materials • Three types of material expelled from volcanoes

  12. Volcanic materials A. Lava (“the liquid”) • Molten rock

  13. Volcanic materials A. Lava • Molten rock • Si affects viscosity

  14. II. Volcanic materials A. Lava 1) Pahoehoe lava • Basaltic lava • Low viscosity

  15. II. Volcanic materials A. Lava 1) Pahoehoe lava • Basaltic lava • Low viscosity • Cools moderately slowly • Ropelike appearance

  16. II. Volcanic materials A. Lava 2) Aa lava (pronounced aa-aa) • Basaltic lava • Higher viscosity • Solidifies while flowing • Angular pieces

  17. II. Volcanic materials A. Lava 3) Pillow lavas • Lava extruded underwater • Cools and contracts • Spherical masses • Ocean floor

  18. II. Volcanic materials A. Lava (“the liquid”) B. Ash and pyroclastic material (“the solid”) • Airborne material ejected by a volcano • Classified based on size:

  19. B. Ash and pyroclastic material (“the solid”) * Volcanic ash • Fine ash - <0.06mm • Coarse ash – 0.06mm to 2mm • Composition = rock, mineral, and volcanic glass

  20. B. Ash and pyroclastic material (“the solid”) * Cinders • 2 mm and 64 mm • Composition - same as ash • Hazardous when falling

  21. B. Ash and pyroclastic material (“the solid”) C) Bombs • Larger than 64mm • Molten rock solidifies in the air • Shapes vary

  22. II. Volcanic materials C. Volcanic gases (“the gases”) • Volatiles • H2S – Hydrogen sulfide • H2O – Water vapor • SO2 – Sulfides • CO2 – Carbon dioxide • N2 – Nitrogen • HCl – Hydrochloric Acid • Significance?

  23. II. Volcanic materials A) Determines violence of an eruption • High gas = violent eruptions • Violent eruptions = felsic magmas • High viscosity magma traps gas • Expansion is prevented, pressure builds

  24. II. Volcanic materials B) Effects on global climate • CO2 – Greenhouse gas • SO2 – Blocks sunlight

  25. II. Volcanic materials • Hazards to humans • Clouds of CO2 get released • Travels across the ground

  26. III. Volcanic Landforms

  27. III. Volcanic Landforms • An erupting volcano will produce a number of distinct landforms including: A. Volcanic cones B. Flood basalts C. Calderas

  28. A. Volcanic cones Three types of volcanic cones:

  29. A. Volcanic cones 1) Shield volcanoes • Multiple layers of basaltic lava • Shallow sides due to magma’s low viscosity • Gentle eruptions

  30. A. Volcanic cones 1) Shield volcanoes • Tall volcanoes –3 or 4 miles tall • Wide base – Diameter of ten of miles

  31. A. Volcanic cones • Mauna Loa volcano, Hawaii

  32. A. Volcanic cones 2) Cinder cones – • Smallest volcanic cone • Layered ash and cinders Ex: El Paricutin

  33. A. Volcanic cones 2) Cinder cones • Short, narrow cone, • Steep sides • Violent eruptions

  34. A. Volcanic cones Lassen National Monument, CA

  35. A. Volcanic cones 3) Composite or stratovolcanoes – • Layered ash, lava, and mud • Intermediate to felsic lava • Steep sides, due to lava’s high viscosity

  36. A. Volcanic cones 3) Composite or stratovolcanoes – • Tall volcanoes – 1 to 2 miles high • Violent eruptions

  37. A. Volcanic cones • Mt. St. Helens, WA

  38. III. Volcanic Landforms B) Flood basalts • Large outpourings of basaltic lava • Multiple, quiet eruptions • Lava plateau

  39. B) Flood basalts • A portion of the Columbia Flood Basalts in WA

  40. III. Volcanic Landforms C) Calderas • Large depressions (> 1km) from violent eruptions • Ugashik Caldera, AK

  41. C) CalderasTwo methods of formation: Method 1: Volcano rapidly empties its magma chamber, and support is lost

  42. C) Calderas Method 1 (cont.): • Overlying material collapses into magma chamber • Caldera forms

  43. C) Calderas Ex: Crater Lake, OR

  44. C) CalderasTwo methods of formation: Method 2: Volcano blows its top, leaving behind a void Inside the cone.

  45. C) CalderasTwo methods of formation: Method 2: Volcano blows its top, leaving behind a void Inside the cone.

  46. IV. Volcanic hazards

  47. IV. Volcanic hazards • Lahars (hot mud flows)

  48. IV. Volcanic hazards • Lahars Sources of water • Melting ice caps • Excess rainfall

  49. IV. Volcanic hazards B) Nuee Ardentes (Glowing Ash flows) • Clouds of dense gas and debris • French for “glowing cloud” • High speeds and high temperatures

  50. IV. Volcanic hazards • How does a Nuee Ardente form? • Volcano erupts • Hot debris rises • Gravity takes over

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