Download What is a Volcano?

Chapter 7 Lesson 3
Volcanoes
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 coneshaped 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/earthsyste
m/volcanoes/
• See World Book Online Student for a table of
famous volcanoes.