1. Chapter 7 Lesson 3 Volcanoes

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. How Do Volcanoes Form?

8. Where Do Volcanoes Occur?

9. 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.

10. 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.

11. Where Do Volcanoes Occur?
Example: The volcanic
island arc of Japan

12. 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

13. 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

14. 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

15. 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

16. 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.

17. BRAIN POP - VOLCANOES
See World Book Online Student for a table of famous volcanoes.