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Volcano Notes.notebook March 01, 2017
Volcanoes
1. oceanic crust; oceanic and continental crust ex. Ring of Fire (CircumPacific Belt); Mt. St. Helens.
2. Divergent volcanism—mid ocean ridges; rift volcanism
ex. Iceland's volcanoes
3. Hot spots—not near plate boundaries; unusually hot regions of earth’s mantle where mantle material rises to the surface; island chain forms as plate moves over hot spot
ex. Hawaiian Islands
Where do Volcanoes Form?
Volcanic EruptionsWhat determines the type of eruption?
• Composition of magma
• Temperature of magma
• Amount of dissolved gases in magma
Water vapor and CO2
Provides the force to extrude lava
• Viscosity of magma
Hotter magma—less viscous (thinner)
Silica content (high content—high viscosity)
More viscous (thicker)—more violent the eruption
Thinner magma (oceanic); thicker (continental)
• vent—opening in the earth’s crust through which lava flows • crater—bowl shaped depression around a vent at the top of a volcano
• caldera—depression that forms when the top or side of a volcano collapse into the magma chamber
• lava dome—masses of lava pile up around the vent
Parts of a Volcano
Types of Volcanoes
• Shield Volcanoes
> Form on oceanic plates
> Gentle slopes
> nonexplosive eruptions
> ex. Hawaiian Islands
• Composite Volcanoes
> Largest volcanoes
> Most violent eruptions
> Form at convergent oceaniccontinental boundaries (subduction zones)
> Ex. Mount St. Helens.
• Cinder Cones
> steepsloped hill of cinders (or scoria)
> smallest volcanoes
Volcano Status
• Active has erupted in recorded history.
> DYK? There are 539 active volcanoes in the world.
• Dormant Last eruptions hundreds of years ago.
• Extinct Has not erupted in millions of years.