Inside Earth Chapter 3.1Pages 88-92

Volcanoes & 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

Lava

Magma

Crater

Lava Flow

Vent

PipeMagma

Chamber

MagmaRising

VolcanoErupts

Magma / Lava• Magma: melted rock,

gases and water vapor from the mantle. Below the surface

• Lava: magma that reaches the surface– Cools and forms solid

rock.Volcano

Menu

Why does Magma Rise?• Magma is a liquid, so it is

less dense than the solid material around it– Flows upward into 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• Eruption occurs when the gasses rush to the

surface, 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 volcano’s 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 is

made from magma rising to the surface.

Volcano Menu

Lava flow• The river of lava that pours down a volcano

over the land.

Volcano Menu

Exit PassDescribe two different

features of a volcano.

Divergent Boundaries

• Form along the mid-ocean ridge– 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 in

S. America

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.– Ring of Fire formed by the many volcanoes that

rim the Pacific Ocean.

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– Yellowstone formed under the continent

• The plate travels over the hot spot– Created a chain of islands to form

Hawaii

Hot Spot Volcanoes

Exit PassWhat are the 3 stages of a

volcano’s life? Explain one of them.

Lava Flow Crater

Vent

Pipe

Magma Chamber

Ash Cloud

Sill

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2

3

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What to Work On

• Read pages 88-92 in the textbookAnswer the Section 3.1 Review questions

on page 91 (#’s 1-4)

DUE: Friday, November 4th

Project Topics• Iceland• Hotspots (Hawaii)• San Andreas Fault• Tau Tona mine• Mount St. Helens• Deep-sea Vents• Christchurch,

Australia earthquake

• Magnetic stripes / field

• Coral reef atolls• Landslides• Liquefaction• Sinkholes• Satellite mapping• Grand Canyon