Name: ________________________________ Period: ______ Date:________________
How Do Volcanoes Form? (p.D30-D36)
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.
 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.
 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.
 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.
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 plates are moving apart, volcanoes can form at the edge of spreading plates.
o These are called rift volcanoes and they are found deep underwater along midocean ridges.
 Volcanoes also form along the edges of slowly colliding plates where one plate plunges
beneath another.
o Example: The volcanic island arc of Japan
 Sometimes volcanoes can form in the middle of plate over a hot spot.
o Hot spot- a very hot part of the Earth’s mantle, where magma can melt through a
plate moving above it.
o Example: The Hawaiian Islands
Volcanoes Are Classified into Three Types Based on How They Form
 Cinder-Cone Volcano
o Sudden, violent eruption
o Steep cone-shaped mound
o Ex. Mount Paricutin, Mexico
 Shield Volcano
o Slow, gentle eruption
o Low, gently-sloped sides
o Ex. Mauna Kea in Hawaii
 Composite Volcano
o Both violent and gentle eruption
o Cone-shaped mound, steep sides
o 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.
Name: ________________________________ Period: ______ Date:________________
How Do Volcanoes Form? (p.D30-D36)
What is a Volcano?
 Volcano- a place where molten rock, hot gases, and solid rock from deep underground
______________ through an opening in the _______________.
 Beneath every volcano is a source of _____________ that rises to the surface through
cracks in the rock and erupts out of a central opening, or ________ to become lava.
 Once magma comes out of the vent, it is called _____________.
 At the top of the volcano there is a hollow around the vent called a _____________.
How Do Volcanoes Form?
 Magma can collect below a volcano in an area called the _____________________.
 As the magma accumulates the pressure inside the magma chamber _____________.
 When the ______________ becomes too great, the chamber breaks open, and the
magma rises in the volcano.
 If magma reaches the __________, an eruption occurs through the vent of the volcano.
 Erupted material ____________ and _____________ around the vent in a mound.
 After many eruptions it can pile up into a big hill or _______________; this is a volcano.
Where Do Volcanoes Occur?
 The _________________________ 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 _________________
and ___________________ boundaries.
 Where plates are moving ______, volcanoes can form at the edge of spreading plates.
o These are called ____________________ and they are found deep underwater
along mid-ocean ridges.
 Volcanoes also form along the edges of slowly ______________ plates where one
plate plunges beneath another.
o Example: The volcanic island arc of ___________________
 Sometimes volcanoes can form in the middle of plate over a ________________.
o Hot spot- a very hot part of the Earth’s mantle, where magma can ________
through a plate moving above it.
o Example: The _________________ Islands
Volcanoes Are Classified into Three Types Based on How They Form
o ______________________________
o Sudden, violent eruption
o Steep cone-shaped mound
o Ex. Mount Paricutin, Mexico
 ___________________________
o Slow, gentle eruption
o Low, gently-sloped sides
o Ex. Mauna Kea in Hawaii
 __________________________
o Both violent and gentle eruption
o Cone-shaped mound, steep sides
o Ex. Mount St. Helen’s in Washington State
Why Are Only Some Volcanoes Active?

An ______________ volcano is one that has recently erupted and there is a possibility
that it may erupt soon.

A ____________ volcano has not been active for a long time but has erupted in
recorded history.

An ________________ volcano has not erupted in recorded history.