1. Mount Pelee 1902 Mount Pelee St. Pierre 28,000 killed 1 survivor
17 ships in the
harbor destroyed
Ash cloud swept
through town
at 125MPH
Event lasted
5 minutes
Masonry walls
3 feet thick
blown apart
Temperatures
over 10000F

2. Magma
Magma: Molten material consisting of liquid, gas, and a crystals.
1) Basaltic magma: 50% SiO2 , 1-2% gas C
Ca-rich plagioclase feldspar & pyroxene minerals
dark - > 40% dark minerals
tends to be highly fluid, low viscosity
2) Granitic magma: 65-77% SiO2 , 10-15% gas
<8000C temperature
quartz, orthoclase feldspar, Na-rich plagioclase minerals
light colored - < 15% dark minerals
highly viscous - silica tetrahedrons link together to resist flow
Magma which reaches the surface and erupts from a volcano is termed extrusive, such as lavas and ash clouds. That which crystallizes underground is called intrusive or plutonic.

3. Bowen’s Crystallization order of minerals in a basaltic magma
Mg, Fe rich: Dark, dense
Ionic Substitution
1st to melt
Na, K, Al, Si rich
Light-colored, less dense minerals

4. Igneous Rocks
Intrusive
(slow cooling)
Extrusive
(fast cooling)

5. Interlocking Grains
Phaneritic texture
Quartz
Biotite
Feldspar

6. Thin section
Biotite
Feldspar
Quartz

7. Aphanitic Texture
Phenocryst

8. Glass
An amorphous solid--no internal crystalline structure

9. Magma Generation
Partial melting of down-going slab: Si, Al, Na, Ca, K

10. Crystallization Early-forming minerals, such as olivine & pyroxene
and sulfide minerals

11. Plutonic Rock Features

12. Intrusive

13. Intrusive Igneous Rocks

14. Devils Tower

15. Sill

16. Dike, Neck

17. Batholith

18. Sierra Nevada

19. West Coast Batholiths

21. Basaltic Volcanism Generally non-explosive
Basaltic magma: Only 50% SiO2, very fluid
Generally results in lava flows, little ash

22. Mid-Oceanic Ridge
80% of world’s
volcanism

23. Flood Basalts
Over 1km thick

24. Basaltic Lava Flow

25. Columbia River Basalts

26. Hawaii

27. Shield Volcano
Builds up over time, lava flow on top of lava flow

28. Pahoehoe Lava Very fluid, thin, and ropy
Outer crust cools quickly, hardens
Very fluid, thin, and ropy

30. Aa Lava
Thick and chunky
Slow moving

32. Lava Tube
Window

33. Kilauea, Hawaii
Caldera

34. Ocean

35. Kalapana, Hawaii

36. Fountain
Fountain

37. Scoria
Vesicular
Fe & Mg rich
Ejected as
liquid

38. Cone

39. Cinder Cone

40. Mauna Kea