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Volcanos and plates
Key point: most volcanoes form along diverging plate boundaries.
I. Volcanic belts form along the boundaries of earth’s plates.
Volcano –a weak spot in crust where magma comes to the surface.
Ring of fire-major volcanic belt around rim of Pacific Ocean. (90% of volcanoes)
Key point: magma called lava once it hits surface.
2. A volcano forms above a hot spot when magma erupts through the crust and
reaches the surface.
Island arc-volcanoes produced from magma seeping through ocean floor.
Hot spot- material deep within mantle rises and melts-Hawaii formed on hot spot.
Volcanic eruptions
1. When a volcano erupts, the force of the expanding gases pushes magma from
the magma chamber through the pipe until it flows or explodes out of the vent.
Magma chamber-pocket magma collects in.
Pipe-long tube magma rises through
Vent-molten rock and gas leave through
Crater- bowl shaped area formed at top of volcano.
2. A volcanoes eruption can be quiet or explosive depending on its content of
water and silica.
Pyroclastic flow- explosion eruption of ash, bombs, cinders and gas.
3. Dormant (sleeping), active (is alive) or extinct (gone, dead) determine a
volcanoes stage of activity.
Volcanic Landforms
Key point: volcanic activity is responsible for building up much of earth’s surface.
1. Volcanic eruptions create landforms made of lava, ash and other materials.
Shield volcano-low silica slow steady flows, short gently sloping volcano with
layers of lava (Hawaii)
Composite volcano-tall cone shaped with layers of lava then layers of ash.
Cinder cone volcano-high silica, explosive, steep cone shaped hill
Lava plateau-lava runs out of several small cracks, flows and forms a high area.
2. Landforms created by magma include:
Volcanic neck-magma hardens in volcanoes pipe.
Batholiths-mass of rock formed when a large body of magma cools inside the
crust.
3. Hot springs and geysers are types of geothermal activity that are often found in
areas of present or past volcanic activity.
Geothermal activity-magma beneath earth’s surface heats underground water
Hot spring-formed from heated groundwater near magma
Geyser-fountain of water and steam that erupts from the ground (Old FaithfulYellowstone Park)