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Chapter 12 ContinuedVolcanism

I. VolcanismI. VolcanismA. DefinitionsB. Volcanic SettingsC. Nature of LavaD. Types of VolcanoesE. Benefits of Volcanoes

II. Current Volcanic Activity

Definitions

Volcano: Forms at the end of a central vent or pipe that rises from the asthenosphere and upper mantle throughrises from the asthenosphere and upper mantle through the crust into a volcanic mountain.

Generally a conical shaped hill or mountain built by accumulations of lava flows, tephra, and volcanic ash

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Where do Volcanoes Occur?

Link to Animations Website

Where do Volcanoes Occur?

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Some Terminology

Volcanoes can be active, dormant or extinct.

• A volcano is active, or alive, when it erupts often.

• When a volcano is dormant, or sleeping, it has not erupted for a long time – but it might in the future.

• A volcano is extinct, or dead, when it hasn’t eruptedfor at least 100 000 yearsfor at least 100,000 years.

Nature of Lava

Characteristics of lava depend upon its temperature and viscosityviscosity.

• Higher the temperature, lower viscosity (i.e. the easier the flows)

• Lower the silica content, lower viscosity because silica polymerizes

• Greater gas content, lower viscosity (frothy lava flows more easily)

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Types of Eruptions

• Effusive• Explosive

Types of Volcanoes

Volcanic Landforms:

Ci dCindercone

Caldera

Shield volcano

Plateau basalt

Composite volcanoes

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Shield Volcanoes

Shield volcanoes are very large slightly slopinglarge slightly sloping volcanoes, 6 to 12°, that have gently flowing magmas.

Shield Volcanoes

Figure 12.32

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Plateau Basalts (flood basalts)Plateau basalt: These volcanoes produce a very fluid basaltic magma with horizontal flows. The form of these volcanoes is flat to gently sloping. p g

Figure 12.24

Plateau Basalts (flood basalts)Plateau basalt: These volcanoes produce a very fluid basaltic magma with horizontal flows. The form of these volcanoes is flat to gently sloping. p g

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Caldera Volcanoes

Long Valley Caldera

Long Valley Caldera in California

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Cinder Cone Volcanoes

A cinder cone is a small volcano, between 100 and 400 meters tall, made up of exploded rock blasted out of a central vent at atall, made up of exploded rock blasted out of a central vent at a high velocity

Figure 12.24

Hualalai Volcano

Composite (Strato) Volcanoes

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Composite Volcanoes

Mt. Vesuvius, Italy79 A.D.

St. Augustine, Alaska

Iceland

Composite Volcanoes

Mt. Pinatubo, Philippines• 800 deaths• 15-20 million tons of ash and sulfuric acid

mist were blasted into the atmosphere• Reduction in Earth’s albedo• Decrease in global temperatures

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Composite Volcanoes

Mt. St. Helens, May 18, 1980~57 people killed

Composite Volcanoes

Figure 12.34

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Deadliest Volcanoes

Deadliest Volcanic Eruptions Since 1500 Benefits of a volcano:A.D.

Eruption Year CasualtiesMajor Cause

Nevado del Ruiz, Colombia 1985 25,0001,3 Mudflows3

Mont Pelée, Martinique 1902

30,0001

(29,025)2Pyroclastic

flows2

Krakatau, Indonesia 188336,0001

(36,417)2 Tsunami2

• Fertile soils (Hawaii)• Geothermal Energy (Iceland, Italy,

New Zealand)• Real Estate (Iceland, Japan)

Tambora, Indonesia 1815 92,0001,2 Starvation2

Unzen, Japan 179215,0001

(14,030)2

Volcano collapse,

Tsunami2

Lakagigar (Laki), Iceland 1783 9,0001 (9,350)2 Starvation2

Animations Website

AnimationsAnimations Website

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II. Current Volcanic Activity

http://volcanoes.usgs.gov/

http://volcano.und.edu/