Volcanoes and Plate Tectonics (part 2)

1. Volcanoesand Plate Tectonics (part 2) “an opening in the Earth’s crust through which an eruption takes place”

2. VolcanoesThree types • Cinder Cones

3. Cinder Cone

4. Inside a Cinder Cone

5. Cinder Cone • Steep sloped sides (angles close to 40°) • Relative to other volcanoes – small few hundreds of meters high • Small explosive eruptions • Made up of pyroclastic material (ash and tephra)

6. Shield

10. Montserrat Volcano eruption

12. Shield Volcanoes • The volcano have a very broad base, with gently sloping side (like a ‘shield’) • Quiet eruptions • Made up of layers of hot, mafic (basaltic) lava • Hawaii is a good example of a shield volcano

13. Composite

15. Mount Saint HelensMay 15, 1980

16. Mount Saint HelensMay 18 1980

17. Mount Saint HelensMay 18, 1980 Eruption

18. Mount Saint HelensMay 18 1980

20. Mt. St. Helens devastation

21. Mount Saint Helens September 10, 1980

23. Mount Saint HelensSeptember 24, 1984

24. Mount Saint Helens (from Spirit Lake) May 15, 1980

25. Mount Saint Helens (from Spirit Lake) May 19,1982

27. Popocatepetl composite volcano in Mexico is on the Ring of Fire

29. Composite Volcanoes • Steep sloped sides • Very tall, 1000s of meters • Very explosive eruptions, sometimes quiet eruptions (alternating for the most part) • Made up of alternating layers of lava flows and silica rich (granitic) pyroclastic material. • Mt. St. Helens is a good example of a composite volcano

30. Volcanoes (cont.) Kinds of Eruptions: Quiet Shield Volcanoes – broad base, low angle slope • Pillow lava – lava that occurs in mid-ocean ridges • Basalt Plateaus – lava spreading evenly over a large area

31. Volcanoes (cont.) Kinds of Eruptions: • Rift Eruptions – Opening in the crust “spreading centers”: • sea floor spreading (ocean) • rift valley (continent) Lava ‘oozes’ out because of its mafic or basaltic composition

33. Areas of Volcanic Activity(kinds of eruptions) Same regions as Earthquakes, which often serve as warning signs that a volcanic eruption might occur. • Ring of Fire – around the rim of Pacific Ocean, subduction zone • Ocean Ridge system • Hotspots

34. Volcanoes (cont.) Kinds of Eruptions: Ring of Fire – Subduction boundary Eruptions – Cinder cones and Composite Volcanoes Explosive eruptions, usually young mountain chains – like around the Ring of Fire

35. Hot Spots Hot Spots – a place in the mantle where great amounts of heat are rising through the lithosphere. • Causes of Hot Spots are still unknown – the source of the heat or ‘spot’ remains in the same location while the plate moves over it. • For example: Hawaii

36. Hot Spots

40. Hot Spots

41. Thermal signature of the Hawaiian Islands

42. Plutonic – Igneous Rocks When masses of magma cools beneath the surface, it forms the cores of mountains. • These ‘igneous intrusions’ are called Plutons. Plutons have different names depending on their size and shape

43. Plutonic – Igneous Rocks Small intrusive igneous formations are: • Dikes • Sills • Volcanic Necks • Laccoliths…

44. Plutonic – Igneous Rocks • Laccolith – magma that buldges upward and formed dome mountains. (Henry Mountains, Utah and Black Hills, South Dakota) • Batholith – a LARGE body (> 100 km3) of intrusive igneous rock. Forms the core of most mojor mountain ranges (Sierra Nevada) • Stock – small batholith, less than100 km3

45. Volcanoes

46. Ruby Mountains Batholith

47. La Paz Batholith

50. East side of Sierra Batholith