Volcanoes

1
Volcanoes
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Magma Formation
Volcanic eruptions occur when magma (molten rock)
formed deep within the Earth, rises to the
surface. Magma forms under three conditions ?A
decrease in pressure lowers the melting
temperature ?An increase in the amount of water
in the asthenosphere lowers the melting point ?An
increase in temperature
3
Which of the three magma formation conditions
allow magma to form at a Rift Boundary?
Condition ? The crust is thinner at a divergent
boundary, reducing the pressure. ExampleMid-Atla
ntic Ridge
4
Which of the three magma formation conditions
allow magma to form at a Subduction Boundary?
Condition ? The cooler crust material sinks into
the asthenosphere releasing water within
it. Example Western coast of South America
5
Which of the three magma formation conditions
allow magma to form at a Hot Spot?
Condition ? A plume of hot solid rises 100s of
km through the mantle melting at areas of low
pressure. Example Hawaii
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Characteristics of Magma
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Lava Flows
Lava Flows on Land ? Pahoehoesmooth, winding
surface ? AAsharp jagged surfaces Lava Flows in
Water ? Pillow Lavafingers of pillow like tubes
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Pyroclastic Flows
Trapped gases can explode violently, causing a
pyroclastic flow made of super-heated gases and ?
ash (less than 2 mm)smooth, winding surface ?
lipilli (2 mm to 64 mm)sharp jagged surfaces ?
block or bomb (gt 64 mm)fingers of pillow like
tubes