1. Volcanoes

2. Chapter 9
Pages:
Questions: 1-7, 12, 19,

3. Volcanoes are associated with plate boundaries and hot spots

4. What do you remember about oceanic and continental crust?
Oceanic crust:
Composition?
Continental crust:

5. What do you remember about oceanic and continental crust?
Oceanic crust:
Lower in silicon and oxygen
Higher in magnesium and iron
Continental crust:
Higher in Si and O
Lower in Mg and Fe

6. Who cares about the composition?
Composition determines the explosivity of a volcano

7. Volcanic rock names are based on the composition
Basalt
Andesite
Rhyolite
Lowest % of silicon and oxygen
Intermediate % of silicon and oxygen
Highest % of silicon and oxygen
Oceanic crust
Mixture of oceanic and continental crust
Continental crust
Divergent plate boundaries and hot spots under oceanic crust (Hawaii)
Subduction zones: Ring of Fire (Cascadia subduction zone)
Hot spot under continental crust (Yellowstone)

8. Magma or lava?
Within the crust
On the Earth’s surface

9. Which lava contains the higher percentage silicon and oxygen?
The more silicate tetrahedrons in a lava, the more explosive the volcano.
Which lava contains the higher percentage silicon and oxygen?
Rhyolitic or andesitic lavas

10. Why?

11. Viscosity Resistance to flow
Which test tube contains the fluid with high viscosity? Left? Right?

12. Viscosity: resistance to flow
Lavas with higher percentage of silicon and oxygen have a high viscosity-pasty
Lavas with a lower percentage of silicon and oxygen have a low viscosity-fluid

13. Rhyolitic lava is associated with continental crust
Rhyolite is cooled from
pasty or thick lavas.

14. Andesitic lava is a combination of oceanic and continental crusts
Andesite is cooled from
pasty or thick lavas.

15. Rhyolitic and andesitic lavas produce pyroclastic debris

16. Basaltic lava is associated with oceanic crust
Basalt is cooled from fluid lava.

17. Basaltic eruptions produce lava flows
Pahoehoe flows: smooth, ropey surface

18. What type of lava is produced at each plate boundary or hot spot?

19. Hot Spots The type of lava produced depends on hot spot location
Under oceanic crust?
Under continental crust?

20. Tectonic setting of Hawaii?
Hot spot under oceanic crust

21. Hot spot under oceanic crust
Stationary plume under oceanic crust
Hot plume acts like a Bunsen burner
Melts oceanic crust
Material from the mantle is also added

22. As the Pacific plate moves over the hot spot, a chain of islands form.

23. Hawaii? Basalt Lava fountains
Aa flows: blocky, jagged, slow moving flows
Shield volcanoes are associated with basaltic lava flows.

24. Type of lava produced?
Basalt
Fluid- low viscosity

25. What other tectonic setting would produce basaltic lava flows?

26. Subduction zone: stratovolcanoes

27. Composite Volcano: subduction zones
Steep at summit, less steep at base
Composite Volcano: subduction zones
Built over a long period of time
Can reach over feet

28. Mt. St. Helens versus Kiliauea
Subduction zone
Stratovolcano
Andesitic lava (pasty)
Violent eruptions
Pyroclastic debris
Hot spot under oceanic crust
Shield volcano
Basaltic lava (fluid)
Lava flows

29. Mt. St. Helens: before the 1980 eruption
Bulge: plug that is pushed out by magma within the conduit.

30. Kilauea eruption

31. Caldera Formation: enormous eruption in a short period of time
Rhyolitic lava composition

32. Size Comparison of Volcanic Landforms

33. How is magma produced?

34. Decompression Melting

35. Decompression Melting
Decrease pressure, lower melting temperature

36. Addition of volatiles lowers melting temperature

37. Adding water, lowers the rock’s melting temperature.

38. Gases drive volcanic eruptions