Outline 3 Volcanic Hazards and Risks ESS 315POE

Outline #3 Volcanic Hazards and Risks ESS 315/POE 313 Volcanism and Magma Properties of Magma -composition -dissolved gases -temperature -viscosity Eruptive Styles Nonexplosive Eruptions Explosive Eruptions Volcanoes and Plate Tectonics Shield Volcanoes Strato Volcanoes Pyroclastic Cones Other Features

Volcanic Hazards Primary Effects -lava flows -pyroclastic eruptions -poisonous gas emissions Secondary Effects -mudflows and debris avalanches -flooding (glacial outburst floods) -tsunamis -seismicity -atmospheric effects and climate change Volcanic Hazards along the Cascadia Subduction Zone Predicting Eruptions Monitoring the Movement of Magma -seismic studies -magnetic field changes -electrical resistivity Physical Anomalies and Precursor Phenomena -ground deformation -change in heat output -change in the composition of gases -local seismic activity

Basalt flows will travel great distances and slope angles will reflect low viscosity.

Rhyolite/dacite flows will retain steep slope fronts because of high viscosity.

Mono Craters, California: VEI - 1 -3

Mount Saint Helens: VEI = 5

Mount Pinatubo: VEI 6

Bishop Ash in alluvial fan deposit. Longvalley Caldera: VEI = 7.

Yellowstone Caldera: VEI = 8

Hawaiian Type Eruption

Phreatic Eruption: MSH April 4, 1980 Plinian Eruption: St. Pierre 1903

Low viscosity basalt flows erupted along the East African Rift Zone travel great distances and create broad lava plateaus.

Although basaltic eruptions tend to be effusive, contact with snow and ice can create catastrophic outburst floods.

Volcanism associated with subduction zones tends to be explosive as andesitic and dacitic magma has a relatively high viscosity coupled with high gas content.

Oceanic hotspots produce basaltic shield volcanoes with relatively gentle slope profiles.