Chapter 5 Volcanoes and Volcanic Hazards. The Nature of Volcanic Eruptions All eruptions involve magma/lava The behavior of magma is determined by: Temperature.

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Presentation transcript:

Chapter 5 Volcanoes and Volcanic Hazards

The Nature of Volcanic Eruptions All eruptions involve magma/lava The behavior of magma is determined by: Temperature Composition Gases These factors control the viscosity, which controls the nature of the eruption

The Nature of Volcanic Eruptions Viscosity - resistance to flow Dictates eruptive behavior High viscosity (cooler) – thick (like stew) Low viscosity (hotter) – very fluid (like soup)

High Viscosity High silica content (Felsic) Andesite & Rhyolite (Granitic) Violent eruptions Continental

Low Viscosity Low silica content (mafic) Basalt Mild eruptions Oceanic

Dissolved Gases in magma/lava Dissolved water in magma reduces viscosity Gases expand within magma as it ascends (decreasing pressure) The violence is related to how easily the gases escape

The Nature of Volcanic Eruptions Quiescent Hawaiian –Type Eruptions Basaltic lavas (low viscosity) Weeks, months or years of lava flowing Explosive Eruptions Granitic (high viscosity) Expels particles of fragmented lava and gases

Other Volcanic Materials Pyroclastics – “fire fragments” Ash/Dust - fine & glassy Pumice - porous Cinders - pea-size Lapilli - walnut-size Blocks – hardened or cooled lava Bombs – hot lava

Development of Pyroclastic Flows

Volcanic Features

Crater Lake

Volcanic Landforms Crater Lake and Wizard Island

Volcanic Landforms Fissure Eruptions & Basalt Plateaus

Shield Volcanoes

Cinder Volcano

Composite/Strato Volcano

Caldera Volcano - Yellowstone

Profiles of Volcanoes

Mt. St. Helens Prior to the 1980 Eruption

Mt. St. Helens after the 1980 eruption

Mt. St. Helens

Shiprock, New Mexico

Plate Tectonics & Igneous Activity Igneous activity is not random Most volcanoes are in/near oceans Basaltic rocks = oceans & continents Granitic rocks = continents

Volcanoes of the Cascade Range

World’s Major Volcanoes

Plate Tectonics & Igneous Activity Intraplate volcanism Occurs within a tectonic plate Hot Spot Hawaii Yellowstone Park

Volcanoes & Climate Explosive eruptions Emit gases & fine-grained debris Solar radiation is reflected & filtered

Volcanoes and Climate Mount Tambora, Indonesia – 1815 Krakatau, Indonesia – 1883 Mount St. Helens, Washington – 1980 Mount Pinatubo, Phillippines

Mount Vesuvius 79 A.D.

End of Chapter 5