Ch 6 Topic Summary

Ch 6 Topic Summary  What Is and Is Not a Volcano? o What Are the Characteristics of a Volcano? Vent & crater present, erupted from fissure or depression, erupt lava or ash o ls Every Hill Composed of Volcanic Rocks a Volcano? No, only hills with vents o What Are Some Different Types of Volcanoes? Scoria/cinder cone (narrow), shield volcano (BIG), composite/strato (lateral cone), volcanic dome (blocky)  What Controls the Style of Eruption? o What Are Ways That Magma Erupts? Water, vertical fountain, dome under surface, ash column o How Do Gases Affect Magma? Dissolved gas held in magma by pressure, less pressure creates gas bubbles, finally an opening releases dissolved gas propels eruption and forms ash, o How Does Viscosity Affect Gases in Magma? More viscous = trapped gas. Less viscous = gas escaping  What Features Characterize Basaltic Volcanoes? o What Are Scoria Cones and Basalt Flows? Scoria cones create mafic rocks which turns into basalt. Trapped gas creates vesicular basalt o How Do Scoria Cones and Basalt Flows Form Around the Same Vent? Early formation of a scoria cone looks like a dome, leaking magma switches to lava flows. Erupt -> make a layer -> repeat o What Do Scoria Cones and Basalt Flows Look Like? Incense cones  How Do Shield Volcanoes Form? o What Is a Shield Volcano? HUGE (around 100 km diameter), fluid magma fed by fissures and scoria cones. Can have craters or small calderas. o How Do Shield Volcanoes Erupt? Fissure eruption, lava flow from central vent, erupt into water and create pillow basalt  What Causes Flood Basalts? o What Are Flood Basalts? Can happen in a continental _ and erupts mafic o How Do Flood Basalts Erupt onto the Surface? Thick fissure -> large volume; thin fissure -> small volume o Where Does the Magma for Flood Basalts Originate? Rising mantle plume under lithospheric mantle -> plume flattens against lithosphere, partially melts -> Plume spreads with additional melting of lithosphere  What Are the Hazards of Basaltic Eruptions? o What Hazards Are Associated with Eruptions of Basaltic Scoria and Ash, and Gas? Hazards = lava flows, pyroclastic flows, lava fountain; gas release can be toxic o How Do Basaltic Eruptions Cause Floods of Water, Ice, and Debris? Eruption near ice sheets causes floods  What Are Composite Volcanoes? o What Are Some Characteristics of a Composite Volcano? Very explosive o What Types of Rocks and Deposits Form on Composite Volcanoes? Felsic, Andesite, tephra, tuff, rhyolite