Kao Fuji Mayan

Bali

Pinatoubo

Pinatoubo

Caldera collapse “normal faults”

Stages of the Yellowstone Caldera ‘resurgent caldera”

Cinder Cones Stratovolcanoes Gas Content Fountains: shields and plateaus Domes Viscosity

Classification of Igneous Rocks Figure 2-5. Classification of the pyroclastic rocks. a. Based on type of material. After Pettijohn (1975) Sedimentary Rocks, Harper & Row, and Schmid (1981) Geology, 9, 40-43. b. Based on the size of the material. After Fisher (1966) Earth Sci. Rev., 1, 287-298.

FeO , MgO, CaO Wt. % oxides Na2O, K2O H2O 45 75 Wt. % SiO2

Water Saturation Exsolution of a vapor Water content (wt. %) of a magma Basalt Andesite Rhyolite Composition

Fractional Crystallization Basalt Andesite Rhyolite low H2O Explosive volcanism ? 50 % SiO2 75% SiO2 Water content of a rhyolitic magma ????

Mt. St. Helens

Granites

Origin of Andesites Fractional crystallization of basaltic magma Contamination of basaltic magma by continental crust Both of the above Partial melting of “special (wet ?) mantle”

Origin of Granite/ Rhyolite Fractional crystallization of basaltic magma ( volume problem for some areas) Partial melting of continental crust