1. Chapter 3: Volcanoes

2. Chapter 3.1
Key Concepts:
Where are Earth’s volcanoes found?
How do hot spot volcanoes form?

3. Definitions:
Volcano: a weak spot in the Earth’s crust where molten material (magma) comes to the surface
Magma: a molten mixture of rock forming substances, gases and water from the earth’s mantle.
Lava: when magma reaches the Earth’s surface.

4. Volcanoes & Plate Boundaries
600 active volcanoes on land, many more under the sea.
Volcanoes occur in belts that extend across continents and oceans.
Ring of Fire - major volcanic belt formed by the many volcanoes that rim the Pacific Ocean.

5. Volcanic belts form along the boundaries of Earth’s plates

6. Volcanic belts form along the boundaries of the Earth’s plates
Diverging ( )and converging () occur.
Results in fractures in the Earth’s crust
Magma reaches the surface.

7. Most volcanoes occur at
Divergent Boundaries
Mid Ocean Ridge
Convergent boundary
Points of subduction
ex. Mount Etna – Eurasian and African plates

8. Volcanoes on Divergent Boundaries
Under ocean: point of Mid ocean ridges occurring ( long underwater mountain ranges)
Many have rift valleys down the center
Lava pours out of rift valley – creates new mountains.
Land - Great Rift Valley in East Africa

10. Volcanoes on Convergent Boundaries
Volcanoes form when:
Two oceanic plates collide
Oceanic and continental plates collide
In both situations, oceanic plates sink beneath a trench.
Rock above the plate melts to form magma.
Erupts to the surface as lava

11. Volcanoes on Convergent Boundaries

12. Volcanoes on Convergent Boundaries
Magma – less dense than the surrounding rock
Magma rises to the surface and breaks through the ocean floor creating volcanoes.
String of islands formed: Island arc
Examples: Japan, New Zealand, Indonesia, the Philippines

13. Hot Spot Volcanoes
Hot Spot – an area where material from deep within the mantle rises and melts forming magma
Volcanoes form above a hot spot when magma erupts through the crust and reaches the surface.

14. Hot Spot Volcanoes
Some hot spots lie in the middle of plates far from plate boundaries.
Others occur on or near plate boundaries.

15. Hot Spot Volcanoes
A hot spot in the ocean floor can gradually form a series of volcanic mountains
Ex. The Hawaiian islands

16. Hot Spot Volcanoes A hot spot can also form under continents
Ex. Yellowstone National Park, WY