1. Chapter 3 Lesson 3
Volcanoes

2. Where are volcanoes found?
Volcanoes form on land and on the ocean floor.
Volcanoes are only located in certain places on the Earth’s surface.
Volcanoes are found where two plates meet.

3. Where are volcanoes found?

4. Where are volcanoes found?
A circle of volcanoes called the Ring of Fire, surrounds the Pacific Ocean.
Volcanoes are more likely to erupt at plate boundaries than anywhere else on Earth.
An eruption is an outpouring of melted rock, ash, gases, or a combination of these.

5. Volcanoes

6. Where are volcanoes found?
However, volcanoes do not erupt at all plate boundaries.
What makes some plate boundaries likely places for volcanoes to erupt?
Scientists conclude that volcanoes tend to erupt where one plate is pushed under another plate.

7. Where are volcanoes found?
When rocks in the plate that is being pushed down reach the heat and pressure in the mantle, they melt
Magma forms and pools in a chamber underneath the crust.
The magma may rest quietly for hundreds or thousands of years.

8. Where are volcanoes found?
Sometimes, a crack forms above the chamber or the pressure in the chamber grows too great to be held in by the rock above it.
Then the magma rushes upward toward Earth’s surface.
All volcanoes have at least one vent, or opening. Once magma reaches Earth’s surface, it is called lava.

9. Volcanoes

10. Volcanoes Over time, a cup-shaped depression may form around a vent.
This depression is called a crater.
Sometimes the magma chamber beneath a volcano is emptied. The volcano may then collapse inside itself.
The hole that forms is called a caldera.

11. How do volcanoes affect land areas?
Gentle Eruptions: Some volcanoes allow these gases to escape without a great deal of pressure building up.
These gentle eruptions produce large amounts of lava, but few explosions.
Eruptions in Hawaii are usually of this type.

12. How do volcanoes affect land areas?

13. Explosive Eruptions Other volcanoes do not let gases easily escape.
The pressure in the magma chamber builds until an explosion occurs.
These volcanoes throw ash, rock, and lava high into the air.
The rock and ash can land far from the erupting volcano.

14. Explosive Eruptions

15. Explosive Eruptions

16. Warning Systems
Scientists can often predict when a volcano is about to erupt.
Small earthquakes cause by magma rising to the surface usually occur.
A tiltmeter is a tool that measures small changes in the tilt of the earth’s surface. They are used to monitor volcanoes.

17. Warning Systems
As magma pushes upward, in a volcano, the Earth’s surface will lift and tilt.
A tiltmeter can detect changes and alert scientists of the data.

18. How do volcanoes build land?

19. How do volcanoes build land?
Dike: Hardened magma, in vertical cracks.
Sill: Hardened magma formed in horizontal layers of rock.
Laccolith: Magma pushed upward and forms a dome shape.
Batholith: largest and deepest of all underground magma, huge and irregularly shaped.

20. How do volcanoes build land?
Vent: Opening where magma comes out of the Earth.
Active volcano: erupting or has recently erupted.
Dormant volcano: volcano that does no erupt for some time.
Extinct volcano: volcano that has stopped erupting. Considered dead.

21. How do volcanoes build land?

22. How do volcanoes build land?
Shield volcano: built by thinner, fluid lava that spreads over a large area. Broad base and gently sloping sides.

23. How do volcanoes build land?

24. How do volcanoes build land?
Cinder-cone volcano: built by thick lava that is thrown high into the air and falls as chunks or cinders. These mountains form as a cone shape with a narrow base and steep sides.

25. How do volcanoes build islands?
Island chain: Hawaiian Islands are a line of volcanic mountains.
Islands form as plates pass over a stationary pool of magma called a hot spot.

26. How do volcanoes build islands?

27. How do volcanoes build islands?