VOLCANO NOTES

1. VOLCANO NOTES

2. There are 2 types of volcanism Intrusive----magma cools below the surface and makes plutons (igneous intrusions) Extrusive---liquid rock lava cools on the surface (volcanoes, lava plateaus)

3. Igneous Intrusions Dikes • Small magma intrusions (no more than a few 100 m wide) • Cut across other rock layers • Force their way along lines of weakness such as faults.

4. Shiprock, NM ---volcanic plug and dike

5. Dike

6. Igneous Intrusions Sills • Small magma intrusions (no more than a few 100 m wide) • Run parallel to rock layers • Force their way along lines of weakness such as bedding planes.

7. A sill in the Salt River Canyon, Arizona

8. COLUMNAR JOINTING Form in sills and dikes that cool slowly and form six-sided columns These pictures were taken on Oregon 19, just north of US 20

9. Columnar jointing in basalt at Devil’s Postpile near Mammoth Lakes, CA

10. Top of jointed basalt columns, Devil’s Postpile, CA

13. Igneous Intrusions Laccoliths - • Lens shaped igneous intrusion • Have a “floor”---there are sedimentary rock layers beneath the base Batholiths - • larger • have no “floor”

14. A batholith exposed by erosion

15. Enchanted Rock batholith; exfoliation dome

16. Intrusive Igneous Bodies

17. Locations of some of Earth’s major volcanoes

18. Active, Dormant, or Extinct? • A volcano is active, or alive, when it erupts often. • When a volcano is dormant, it has not erupted for a long time – but it might in the future. • A volcano is extinct when it hasn’t erupted • for at least 100,000 years.

19. Types of Eruptions Depends on trapped gases and magma composition • Violent and explosive • Quiet and flowing

20. http://dsc.discovery.com/convergence/pompeii/videogallery/videogallery.htmlhttp://dsc.discovery.com/convergence/pompeii/videogallery/videogallery.html

21. Trapped Gases • Water vapor and carbon dioxide are trapped in magma • At low pressure, they escape quietly when they reach the surface • At high pressure, they escape violently when they reach the surface

22. Magma Composition • Two types: • Basaltic – less silica and very fluid; produces quiet eruptions • Granitic – lots of silica, high water vapor content, and very thick; produces very violent eruptions

23. GLOSSARY Bomb – a lump of rock thrown out in an eruption Crater – a deep hollow at the top of a volcano Lava – melted rock that flows down the volcano Magma – melted rock inside the Earth Molten – melted, liquid Vent – a crack on the side of a volcano where magma can escape

24. Forms of Volcanoes • Three forms: • Shield • Cinder Cone • Composite

25. Shield Volcano • Formed by quiet eruptions • Basaltic lava builds up in flat layers • Gently sloping sides • Ex: Hawaiian Islands (Mauna Loa)

26. Shield volcano

27. Mauna Loa in background Kilauea is behind Mauna Loa (erupting since 1983) Mauna Kea Shield volcano Hot Spot

28. Kilauea

30. Pahoehoe (smooth, ropy) lava flow

31. aa lava flow (slow, chunky)

34. http://www.learner.org/interactives/volcanoes/movies/movies3.htmlhttp://www.learner.org/interactives/volcanoes/movies/movies3.html

35. Cinder Cone Volcano • Caused by explosive eruptions • Granitic lava thrown high into the air • Lava cools into different sizes of volcanic material called tephra • Steep-sided, loose slopes • Ex. – Paricutin (Mexico)

36. Cinder cone

38. Composite/Stratovolcano • Alternating layers of ash and lava • Quiet or violent • Basaltic or granitic • Steep or gentle slopes • Ex. – Mt. St. Helens

39. Composite volcano

40. Guagua Pichincha, Ecuador Quito in foreground Composite volcanoes - explosive

41. Arenal Volcano – Costa Rica Photo by E. L Crisp, 2007

44. Mt. St. Helens – a typical composite volcano

45. Mt. St. Helens following the 1980 eruption

46. http://www.youtube.com/watch?v=bgRnVhbfIKQ&feature=related

47. Nueéardente (hot pyroclastic flow) on Mt. St. Helens

48. Mt. Vesuvius – 79 a.d.

49. A lahar (mud flow caused by melting snow) along the Toutle River near Mt. St. Helens

50. Composite Volcano Mt Rainier Subduction zones