1. VOLCANOES

2. 1. Increase Temperature 2. Decrease Pressure 3. Alter Composition (to decrease melting temperature) Melting the Mantle

3. 1. Mid Ocean Ridges (decompression) 2. Hotspots (high temperature + decompression) 3. Subduction zones (add water, decrease melting temperature) Where Does Melting Occur?

4. Magma: result of melting rocks Lava: magma that flows out over the surface Pyroclastic rocks: Rock fragments resulting from explosive volcanism, deposited by sedimentary processes. Volcanic Products

6. Pu ' u O ' o, Hawaii

7. Fire Fountain

10. 1. Viscosity  Depends on SiO2 content  “Mafic” magmas: poor in SiO2, rich in Mg, Fe low viscosity  “Felsic” magmas: rich in SiO2, poor in Mg, Fe high viscosity Controls on Eruptive Style

11. 2. Volatiles  H2O and CO2  “Dry” mantle rocks generate mafic magma “Wet” mantle rocks generate felsic magma  Volatiles decrease magma viscosity when dissolved Controls on Eruptive Style

12. 1. Fissure eruption 2. Shield volcano 3. Pillow basalts 4. Domes & Cones 5. Strato-volcano Subaerial eruption, low viscosity magma Submarine eruption, low viscosity magma Subaerial eruption, high viscosity magma } } Eruption Style

15. Fissure eruption: Krafla, Iceland

17. Hexagonal cooling joints in basalt: Devil's Postpile, California

18. Hexagonal cooling joints in basalt, e.g. Giant’s Causeway, Antrim

25. Sunset Crater, Arizona Bonito Flow Cinders

26. Cerro Negro, Nicaragua 1947 eruption