1. MAGMA is molten rock, but is not just liquid - also contains bits of rock crystals and gas. It ranges in consistency from wet concrete to thick oatmeal.
Rock that crystallizes from a magma is IGNEOUS ROCK.

2. large crystals tiny crystals no crystals
Phaneritic Aphanitic Glassy
large crystals tiny crystals no crystals
slow cooling fast cooling very fast cooling
Ex/ Gabbro Basalt Obsidian (all the same composition – of ocean seafloor)

3. Rock melts when the temperature within the earth (geotherm) exceeds the melting point (solidus) of rock.
This happens for different reasons at (1) subduction zone volcanoes, (2) mid-ocean ridge volcanoes, and (3) hotspot volcanoes.

4. Normally the geotherm does not cross the solidus, so there is no melting.
BUT, it is very close at about km in depth ( Asthenosphere).

5. What are the 3 main causes of volcanoes?
1. Mid-Ocean Seafloor Spreading

6. Ridges: “pressure release” melting

10. What are the 3 main causes of volcanoes?
2. Seafloor Subduction

11. Subduction Zones: “wet” melting

13. Mt. Fujiyama

15. Pyroclastic flow sweeps down the side of Mayon Volcano, Philippines, 1984.

16. A small lahar triggered by rainfall in Guatemala, 1989.

17. Mt. Pinatubo, Philippines, 1991.

19. Mt. Pinatubo: So much ash into the atmosphere that Earth’s temperature dropped, and sunsets were redder.

20. What are the 3 main causes of volcanoes?
3. Hotspot Mantle Plumes

21. Hawaii rises more than 5 miles above the seafloor.

22. Hawaii

23. Kilauea, Hawaii
Mauna Loa, Hawaii

24. Pahoehoe lava, Hawaii

25. “Aa” lava flow, Kilauea, Hawaii

26. Kilauea, Hawaii

28. Mt. St. Helens:
Giant Eruption
May 18, 1980

31. Mt. Adams
Mt. St. Helens

33. Crater Lake, Oregon

34. Mt. St. Helens:
Before
May, 1980
After

35. Phase 1: Small earthquakes and puffs of steam indicate that magma is rising. Bulge develops in North face.

36. Phase 2: A magnitude 5.1 earthquake shakes mountain, dislodging bulge which slides down mountain. Decreased pressure on magma starts lateral blast.

37. Phase 3: Eruption causes a second block to break free, exposing more magma and initiating an eruption column. Lateral blast goes at 300 mph, covers 230 square miles.

38. Phase 4: The Eruption Column reaches 80,000 feet in less than 15 minutes.

44. Mt. St. Helens Earthquakes: 1995-2005

45. The Dome is Growing Again

53. Mechanical Weathering (1):
Frost Wedging

54. Mechanical Weathering (2):
Plant growth

55. Mechanical Weathering (3):
Pressure release

56. Mechanical Weathering (4):
Large Temperature changes (also: forest fires)

58. Chemical Weathering (1): Dissolution
Water and carbon dioxide combine to make carbonic acid, which dissolves minerals.

59. Chemical Weathering (2): Hydrolysis
Addition of water to minerals makes clay minerals

60. Hydrolysis: Greatly accelerated in the presence of acidic rain

61. Chemical Weathering (3): Oxidation
Addition of oxygen to a metal-rich mineral forms a new mineral
>> RUST

62. An end product of weathering is SOIL.