1. Volcanoes
Shield Volcano
Typically Basalt
Lava Flows
Low Slope Angle

2. Volcanoes Composite or Strato-Volcano Typically Andesite
Lava Flows and Tuffs (pyroclastic)
Higher Slope Angle

3. Volcanoes Cinder or Scoria Cone Typically Basalt Gas-charged spray
Not very violent

4. Volcanoes

5. Volcanoes Lava Dome Typically Rhyolite
Slow extrusion following violent explosion

6. Volcanoes Spatter Cone Typically Basalt Gas-charged spray
Not very violent
Returns to ground before solidifies

7. Volcanoes
Vent vs. Fissure

8. Volcanoes
Plateau Basalt Eruptions

9. Volcanoes
Plateau Basalts are Fissure Eruptions

10. Volcanoes
Columnar Joints

12. Caldera Formation

14. Volcanic Hazards
Lava Flows
Basalt flows in Kalapana area, Hawaii

15. Volcanic Hazards
Geologists outpace lava in Hawaii!

16. Basalt from Mt Nyiragongo invades Goma, Congo, 2002
Volcanic Hazards
San Juan Parangaricutiro engulfed by basaltic aa from Paricutin, 1944
Lava Flows
Basalt from Mt Nyiragongo invades Goma, Congo, 2002

18. Volcanic Hazards
Wind-blown ash deposits
Heimay, Iceland
Ash

19. Volcanic Hazards
Ash
Vertical plinian ash column from Mt. St. Helens, 1980
Mount Pinatubo, Philippines, on June 12, 1991

20. Volcanic Hazards
Ash

21. Volcanic Hazards Pyroclastic Flows
Video of pyroclastic flow on Mt. Unzen
Soufriere erupts on Montserrat, August 1997
Glowing ash cloud descends Mt St Helens, August 1980

22. Volcanic Hazards Pyroclastic Flows
St. Pierre, Martinique after Nuée Ardente from Mont Pelée, 1902

23. Volcanic Hazards
Rhyolite Eruptions

27. Plutonic Rocks

29. Plutonic Rocks

30. Igneous Processes

31. Igneous Processes
Hotspots can also create volcanism within continental plates
Subduction zones create chains of volcanoes
Melting creates volcanoes (e.g. Iceland) and oceanic crust at divergent plate boundaries
Mid-Ocean Islands (e.g. Hawaii) created at enigmatic “hotspots” with elevated T

32. Igneous Processes
More Mafic
(and last to melt)
More Sialic
(and first to melt)
Partial melts: low-T fraction is always more Si-Al-Na-K-rich and Fe-Mg-poor than source rock.
Leaves behind Mg-Fe-rich refractory residue

33. Igneous Processes Geotherm Liquid Solid
Decompression partial melting at divergent zones
Partial melts: low-T fraction is always more Si-Al-Na-K-rich and Fe-Mg-poor than source rock.
Leaves behind Mg-Fe-rich refractory residue

34. Igneous Processes
Decompression partial melting at divergent zones

35. Igneous Processes
“Hot Spots”

36. Igneous Processes
“Hot Spots”

37. Igneous Processes
“Hot Spots”

38. Igneous Processes Subduction zones:
Conveyor of basalt to melt ® andesite
Water lowers melting point of mantle wedge

39. Igneous Processes
Subduction zones: water lowers melting point

40. Magma Generation and Evolution

41. Magma Generation and Evolution
More Mafic
Crystal Fractionation
(and last to melt)
More Sialic
(and first to melt)