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CH 6 Prentice Hallp.178-181
CH 6 Prentice Hallp.178-181
Volcanoes & Volcanoes & Plate Tectonics
Plate Tectonics
What is a Volcano?
• A weak spot in the crust where molten material, or magma comes to the surface.– Volcanic Activity is a constructive force that adds
new rock to existing land or forms new islands.
Volcano Menu
Magma / Lava
• Magma- a mixture of rock forming substances, gases and water vapor from the mantle.
• Lava- Magma that reaches the surface.– Cools and forms solid
rock.
Volcano Menu
Magma Rises
• Magma is a liquid- therefore it is less dense than surrounding solid material.– Flows upward into any
cracks in the rocks above.– Rises until it reaches the
surface or becomes trapped beneath layers or rocks.
Volcano Menu
Volcano Erupts
• Dissolved gases trapped in magma are under tremendous pressure.
• The gasses dissolved in magma rush out, carrying magma with them.
Volcano Menu
Crater
• Lava collects in the crater, the bowl-shaped area that forms around the volcano’s vent.
Volcano Menu
Vent
• The point on the surface where magma and gas leave the volcanoes pipe.
Volcano Menu
Pipe
• A narrow, almost vertical crack in the crust through which magma rises to the surface.
Volcano Menu
Magma Chamber
• A large underground pocket of magma that forms from magma rising to the surface.
Volcano Menu
Lava flow
• The river of lava that pours down a volcano over the land.
Volcano Menu
Stages of a Volcano
• Active:– A live volcano that is erupting or shows signs that
it may erupt in the future.
• Dormant:– A sleeping volcano. It may awake in the future
and become active.
• Extinct:– A dead volcano. It is unlikely to erupt again.
Location of Volcanoes
• Most occur along diverging boundaries such as the mid-ocean ridge or in subduction zones.
Location of Volcanoes• About 600 active volcanoes on land, more lie
beneath the sea.• Occur in belts that extend across continents
and oceans.• Ring of Fire-formed by the many volcanoes that rim the
Pacific Ocean
Divergent Boundaries
• Form along the mid-ocean ridge.– Ridge a long underwater
rift valley.– Lava pours out of the
cracks in the ocean floor.
• Iceland- is a volcano on the mid-ocean ridge that has reached the surface.
Convergent Boundaries
• Plates collide– Denser plate subducts towards the mantle.• Forms a deep-ocean trench• The crust melts and forms magma that rises.• Rising magma erupts through a volcano on the surface.
Convergent Boundaries
• Ocean/Ocean– Denser ocean plate subducts• Forms a deep sea trench• Forms an island arc of
volcanoes.– Japan– New Zealand– Aleutians
Convergent Boundaries
• Continent to Ocean– Dense ocean plate
subducts• Forms a deep sea trench• Forms volcanoes on the
land. – Mt. St Helens– Andes Mountains-S.
America.
Hot Spot Volcanoes• An area where magma from deep
within the mantle melts through the crust like a blow torch.
• Lie in the middle of plates.– Hawaii- formed in the middle of the
Pacific Ocean plate. – Yellowstone- formed under the continent.
• The plate travels over the hot spot.– Created a chain of islands to form Hawaii
Hot Spot Volcanoes