1. Volcanoes Chapter 5
S6E5: Convection currents cause plate movement which causes geologic activity such as volcanoes.

2. A weak spot in Earth’s crust where magma comes up to the surface
What is a VOLCANO?
A weak spot in Earth’s crust where magma comes up to the surface

4. Where are most of Earth’s major volcanoes located?
In belts around the Earth’s continents and oceans along plate boundaries
One major belt is known as the Ring of Fire, located around the rim of the Pacific Ocean

6. Volcanoes at Divergent Boundaries
May form in the ocean at mid-ocean ridges
May form on continents at rift valleys

7. Example: Great Rift Valley in East Africa

8. Volcanoes at Converging Boundaries
Form where 2 plates collide:
Oceanic  Continental
Oceanic  Oceanic
The resulting volcanoes create a
string of islands called an
Island Arc

9. Examples of Island Arcs: The Aleutian Islands

10. Another Example of an Island Arc: The Carribean Islands

11. Volcanic Hot Spots
A volcano forms above a Hot Spot when magma erupts through the crust and reaches the surface

12. Oceanic Hot Spot: The Hawaiian Islands

13. Continental Hot Spot: Yellowstone National Park, Wyoming, USA

14. Volcanic eruption vary depending on the viscosity of the magma
What is viscosity?
The resistance of a liquid to flow. The greater the viscosity, the thicker the flow
Depends on the amount of silica (from 50% - 70%)

15. Quiet Eruption Volcano erupts quietly
Low silica magma has low viscosity and flows easily
Example: The Hawaiian
Islands

16. Explosive Eruption Volcano erupts violently
High silica magma, high viscosity, thick and sticky, does not flow – builds up pressure
Example:
Mt Saint Helens
Mount St. Helens about noon on May 18, 1980
after being dormant for 123 years.

17. Pyroclastic Flow Volcano erupts violently
Hurls out a mixture of hot gases, ash, cinders, & bombs
Example: Mayon Volcano, Philippines

18. Three Main Types of Volcanoes:
1. Shield Volcano
2. Cinder Cone Volcano
3. Composite Volcano

19. Shield Volcano Gradual, build-up of lava Wide, gently sloping mountain
Example: Hawaiian Islands
Notice the shapes of the shields??? Hummm…

21. Erupts violently, producing ash, cinders, and bombs
Cinder Cone Volcano
Erupts violently, producing ash, cinders, and bombs
Loose materials build up around the vent in a steep cone-shaped mountain
Example: Pariciutin, Mexico

22. Cinder Cone Volcano

23. Composite Volcano
Lava alternates with layers of ash in explosive eruptions
Tall, cone-shaped mountain
Examples: Mt. Fuji, Japan and
Mt. Saint Helens, Washington, USA

24. Composite Volcanoes

25. Mt. Saint Helen’s Before & After eruption

26. Comparing Shield & Composite Volcanoes

27. Comparing the shapes of Volcanoes!

28. Check out this volcano link…

29. Huge hole left by the collapse of a volcanic mountain
What is a Caldera?
Huge hole left by the collapse of a volcanic mountain

30. Geothermal Activity
Hot springs & geysers are types of geothermal activity often found in areas of past or present volcanic activity

31. What are hot springs?
They form when groundwater is heated by nearby magma or hot rock deep underground

32. Which one is a geyser?

33. Seriously, what is a geyser?
A fountain of water and steam that erupts from the ground
Example: Old Faithful at Yellowstone National Park
It erupts ‘faithfully’ every 33 – 93 minutes

34. Experimenting with Volcanic Eruptions
Volcano Info…build & erupt a volcano…have fun!