Download Volcanoes

Volcanoes
Openings in the Earths Crust That
Lets Magma Through and Often
Forms a Mountain.
Parts of a Volcano
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Vent: opening through which magma
reaches the surface.
Crater: Steep depression around the
vent.
Mountain: made of lava flows or tephra
(dust, ash, cinders, bombs)
Magma Chamber: area of magma
below volcano
Where Volcanoes Form
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Divergent Boundaries
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Convergent Boundaries / Subduction Zone
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Plates spread apart and magma flows to surface
Mid-ocean Ridge / East African Rift
Subduction melts one plate, melted material
reaches surface.
Mount St. Helens
Hot Spots
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Area of super heated mantle that a plate moves
over.
Hawaii
Hot Spot Video
Types of Magma
Granitic Magma
Andesetic
Basaltic Magma
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High Silica content
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Intermediate
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Low Silica content
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Thick
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Intermediate
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Runny
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Intermediate
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Little trapped gases
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Intermediate
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Traps lots of gases
Water vapor
Pressure builds
Explosive
Ash eruption
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Fairly explosive
Ash and lava
eruption
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Small pressure build
up
Non-explosive
Lava flow eruption
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Three Types of Volcanoes
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Shield Volcanoes
Cinder Cones
Composite Volcanoes
Shield Volcano
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Hot Spots / divergent plate boundaries
Basaltic magma: runny, little silica, little
trapped gases.
Built by layer upon layer of lava flows.
Lava oozes and flows.
Non-explosive.
Broad flat gentle slopes.
Usually wider than is tall.
Hawaiian Island Shield
Volcano
Cinder Cone
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Subduction Zones / Hot spots
Granitic magma: Thick, high silica, lots
of trapped gases.
Built by piles of tephra (dust, ash,
cinders, bombs).
Explosive.
Steep sides and not very tall.
Composite Volcano
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Subduction Zones
Has things in common with both cinder cone
and shield volcano.
Alternating layers of lava flows and tephra.
Very tall and dormant for years
Cooling lava can seal vent and build pressure.
Mount Rainier
Andesetic Magma
Composite Volcano Video