VolcanoesVolcanoes

Types of EruptionsTypes of Eruptions

•Violent and explosive•Quiet and flowing

–Depends on trapped gases and magma composition

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Trapped GasesTrapped 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

Magma CompositionMagma 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

Forms of VolcanoesForms of Volcanoes

•Three forms:–Shield–Cinder Cone–Composite

Shield VolcanoShield Volcano

•Formed by quiet eruptions•Basaltic lava builds up in flat layers

•Gently sloping sides•Ex: Hawaiian Islands

Cinder Cone VolcanoCinder 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

Composite VolcanoComposite Volcano

•A mix of the other two types

•Quiet or violent•Basaltic or granitic•Steep or gentle slopes•Layered or tephra

Plate Tectonics and Igneous ActivityPlate Tectonics and Igneous Activity

• Most of the volcanoes on Earth occur along the margins of the ocean basins, within the circum-Pacific, known as the Ring of Fire.

• 2nd group is found in the deep-ocean basins, Hawaii and Iceland.

• 3rd group is composed of volcanic structures that are irregularly distributed in the interior of the continents.

Convergent Plate BoundariesConvergent Plate Boundaries• The basic connection between plate tectonics

and volcanism is that plate motions provide the mechanisms by which mantle rocks melt to generate magma.

Convergent Plate BoundariesConvergent Plate Boundaries• Ocean-Ocean

• Volcanism at a convergent plate where one oceanic slabs descends beneath another results in the formation of a chain of volcanoes on the ocean floor.

Convergent Plate BoundariesConvergent Plate Boundaries• Ocean-Continent

• Develop where slabs of oceanic lithosphere are subducted under continental lithosphere to produce a continental volcanic arc.

Divergent Plate BoundariesDivergent Plate Boundaries

• Most magma is produced along the oceanic ridges during seafloor spreading.

Intraplate Igneous ActivityIntraplate Igneous Activity

• Occurs within a plate, not at a plate boundary.• Yellowstone National Park• Most intraplate volcanism occurs where a mass

of hotter than normal mantle material called mantle plume rises toward the surface.

• Caused by hot mantle plumes rising up from the core mantle-boundary, causing decompression melting and forming small areas of volcanic activity on the surface.

ReviewReview

• How are the locations of volcanoes related to the plate boundaries?

• What causes intraplate volcanism?

• Where is most of the magma produced on Earth on a yearly basis?

• What is the ring of fire?