Chapter 7 Lesson 3Volcanoes

What is a Volcano?

• Volcano- a place where molten rock, hot gases, and solid rock from deep underground erupt through an opening in the crust.

What is a Volcano?

• Beneath every volcano is a source of magma that rises to the surface through cracks in the rock and erupts out of a central opening, or vent to become lava.

What is a Volcano?

• Once magma comes out of the vent, it is called lava.

• At the top of the volcano there is a hollow around the vent called a crater.

How Do Volcanoes Form?

• Magma can collect below a volcano in an area called the magma chamber.

• As the magma accumulates the pressure inside the magma chamber increases.

• When the pressure becomes too great, the chamber breaks open, and the magma rises in the volcano.

How Do Volcanoes Form?

• If magma reaches the surface, an eruption occurs through the vent of the volcano.

• Erupted material cools and hardens around the vent in a mound.

• After many eruptions it can pile up into a big hill or mountain; this is a volcano.

How Do Volcanoes Form?

Where Do Volcanoes Occur?

Where Do Volcanoes Occur?

• The Pacific Ring of Fire is an area located by the edge of the Pacific Plate and is known for its volcano and earthquake activity.

• Most volcanoes occur in belts along the edges of plates along convergent and divergent boundaries.

Where Do Volcanoes Occur?

• Where plates are moving apart, volcanoes can form at the edge of spreading plates. – These are called rift volcanoes and they are

found deep underwater along mid-ocean ridges.

• Volcanoes also form along the edges of slowly colliding plates where one plate plunges beneath another.

Where Do Volcanoes Occur?

• Example: The volcanic island arc of Japan

Where Do Volcanoes Occur?• Sometimes volcanoes can form in the middle

of plate over a hot spot.– Hot spot- a very hot part of the Earth’s mantle,

where magma can melt through a plate moving above it.

– Example: The Hawaiian Islands

Volcanoes Are Classified into Three Types Based on How They Form

• Cinder-Cone Volcano– Sudden, violent

eruption– Steep cone-

shaped mound– Ex. Mount

Paricutin, Mexico

Volcanoes Are Classified into Three Types Based on How They Form

• Shield Volcano– Slow, gentle

eruption– Low, gently-sloped

sides– Ex. Mauna Kea in

Hawaii

Volcanoes Are Classified into Three Types Based on How They Form

• Composite Volcano– Both violent and

gentle eruption– Cone-shaped

mound, steep sides– Ex. Mount St.

Helen’s in Washington State

Why Are Only Some Volcanoes Active?

• An active volcano is one that has recently erupted and there is a possibility that it may

erupt soon.• A dormant volcano has not been active for a

long time but has erupted in recorded history.• An extinct volcano has not erupted in recorded

history.

BRAIN POP - VOLCANOES

• http://www.brainpop.com/science/earthsystem/volcanoes/

• See World Book Online Student for a table of famous volcanoes.