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Eruptions and Forms of Volcanoes

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Presentation on theme: "Eruptions and Forms of Volcanoes"— Presentation transcript:

1 Eruptions and Forms of Volcanoes

2 Types of Eruptions Violent and explosive Quiet and flowing
Depends on trapped gases and magma composition

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5 Trapped Gases Water vapor and carbon dioxide are trapped in magma
At low pressure, they escape quietly when they reach the surface At high pressure, they escape violently when they reach the surface

6 Magma Composition Two types:
Basaltic – less silica and very fluid; produces quiet eruptions Granitic – lots of silica, high water vapor content, and very thick; produces very violent eruptions

7 Forms of Volcanoes Three forms: Shield Cinder Cone Composite

8 Shield Volcano Formed by quiet eruptions
Basaltic lava builds up in flat layers Gently sloping sides Ex: Hawaiian Islands

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10 Cinder Cone Volcano Caused by explosive eruptions
Granitic lava thrown high into the air Lava cools into different sizes of volcanic material called tephra Steep-sided, loose slopes

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12 Composite Volcano A mix of the other two types Quiet or violent
Basaltic or granitic Steep or gentle slopes Layered or tephra

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