GEO.416GEO.416 VOLCANOLOGYVOLCANOLOGY I. Physical Nature Of Magmas . 4 Structural State of Silicate Melts . 4 Viscosity . 5 Controls on Viscosity . 5 Silica composition . 6 Temperature . 6 Time . 6 Volatiles . 7 Pressure . 7 Crystal content . 7 Bubble Content . 8 Yield Strength . 8 Specific Heat . 8 Thermal Conductivity . 8 Density . 9 Electrical Conductivity . 9 Seismic Wave Velocities . 9 II. Generation, Rise And Storage Of Magma . 10 Nature of Crust and Upper Mantle . 10 Heat Sources . 11 Mechanisms of Melting . 11 Partial Melting . 11 Segregation and Rise of Magmas Through The Mantle . 12 Rise of Magmas Through Brittle Lithosphere . 13 Flow of Magma . 14 Flow Rates . 14 Nature of Flow Regime . 15 Flow Instabilities . 15 High-Level Reservoirs and Subvolcanic Stocks . 16 III. Eruptive Mechanisms . 18 Opening Of Vents . 18 Mechanisms of Explosive Eruptions . 18 Nature of the Gaseous Eruptive Column . 19 Bubble Nucleation And Growth . 20 Pressure Relations . 20 Ejection Of Pyroclastic Material . 21 Ejection Velocities . 21 Eruption Energy . 22 V. Lava Flows . 23 Volume . 23 Length and Thickness . 23 Velocity of Flow . 24 Discharge Rates . 24 Physical Properties of Lavas . 25 Temperature and Cooling of Lavas . 25 Viscosity . 25 Morphology Of Lava Flows . 26 Pahoehoe Lavas . 26 External Structures of Pahoehoe Lavas . 26 Internal Structures of Pahoehoe Lavas . 27 Aa Lavas . 28 External Structures of Aa Lavas . 28 Block Lava . 29 Internal Structures of Blocky Lavas . 29 Pillow Lava . 30 VI. Volcanic Domes . 31 External Features of Volcanic Domes . 31 Internal Structures of Volcanic Domes . 32 VII. Products Of Volcanic Explosions . 33 Terminology and Classification . 33 Origin . 33 Fragment Size . 33 Airfall Ash Deposits . 35 Dispersal . 36 Structures Of Airfall Deposits . 36 Morphology of Ash Particles . 37 Pyroclastic Flow And Surge Deposits . 37 Relationship to Topography . 38 Flow Units and Cooling Units . 39 Components . 40 Characteristics of Ash-Flow Deposits . 40 Internal Layering . 40 Gas-Escape Structures . 41 Textural Relationships . 41 Segregation of Crystals and Lithics . 42 Temperature Effects . 42 Welding and Compaction . 42 Structures Related to Temperature and Viscosity . ..