Outline #3 Volcanic Hazards and RisksESS 315/POE 313

Volcanism and MagmaProperties of Magma-composition-dissolved gases-temperature-viscosity

Eruptive StylesNonexplosive EruptionsExplosive Eruptions

Volcanoes and Plate TectonicsShield VolcanoesStrato VolcanoesPyroclastic ConesOther Features

Volcanic HazardsPrimary 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 EruptionsMonitoring 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.