THE ROCK CYCLE

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. Viscosity

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

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

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

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

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

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

22. 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

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

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

25. 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?

26. 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

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

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

29. III. Volcanic Landforms

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

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

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

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

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

37. 1996

38. 1996

39. 1996 1997

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

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