1. Types of Volcanoes
Key Concept: Tectonic plate motions can result in volcanic activity at plate boundaries.

2. Volcanoes

3. How do volcanoes work?
Heat and pressure cause rocks to melt and form magma.
Magma needs to get out, too much pressure!!!!!!
Rise in temperature or drop in pressure causes magma to form faster.

4. How do volcanoes work? Magma is forced onto Earth’s surface.
It dries and hardens, this happens many times over thousands of years.
Eventually a mountain called a volcano is formed.

5. Parts of a Volcano Most volcanoes share a specific set of features.
The magma that feeds the eruptions pools deep underground in a structure called a magma chamber.
At Earth’s surface, lava is released through openings called vents.
Flowing lava in the interior travels through long, pipelike structures known as lava tubes.

6. Where do most volcanoes occur?
Volcanoes occur at both divergent and convergent boundaries and also at hot spots.

7. Hot Spots form volcanoes.

8. Prominent Hot Spots Around the World

9. Volcanoes form at convergent plate boundaries.

10. Volcanoes form at divergent boundaries.

11. Volcanoes at Divergent Boundaries
At a divergent boundary, the lithosphere becomes thinner as two plates pull away from each other.
A set of deep cracks form in an area called a rift zone.
Hot mantle rock rises to fill these cracks.
As the rock rises, a decrease in pressure causes hot mantle rock to melt and form magma.
The magma that reaches Earth’s surface is called lava.
Basaltic magma rises to Earth’s surface through these fissures and erupts nonexplosively

12. Why do we have different types of Volcanoes?
The process of magma formation is different at each type of plate boundary.
Therefore, the composition of magma differs in each tectonic setting.
Tectonic settings determine the types of volcanoes that form and the types of eruptions that take place.

13. Viscosity Viscosity is defined as the resistance to flow.
The more viscous magma is, the more explosive the eruption.

14. Types of volcanoes

15. Types of volcanoes
Shield volcano: usually form at hot spots, from non explosive eruptions
Cinder cone volcano: form from explosive eruptions, very steep.
Composite volcano: form from both explosive and non explosive eruptions.

16. Shield volcano
Lava has low viscosity and flows great distances as it cools.
Very wide, not to steep.
Biggest type of volcanoes
Tallest mountain in the world is Mauna Kea (measures from sea floor to top)
non explosive eruptions

17. Mauna Kea, Hawaii

18. Cedar Hill Box Elder County, Utah
Note the classic shield shape of this one million year old volcano.

19. Cinder cone volcano Smallest type of volcano Most common
Form a large crater
Explosive eruption which builds up steep sides.
Gas rich magma erupts explosively into air producing large fragments of solid material called cinders
Lava has high viscosity
Explosive!

21. Paricutin, Mexico

22. Diamond Cinder Cone, Washington County, Utah

23. Cinder cone volcano: Monti Silvestri, Mt. Etna- erupted 1892

24. Composite volcano:
Eruptions alternate between explosive and non-explosive.
Sometimes they have runny lava layers, other times the have pyroclastic materials form layers.
Have a wide base and steep sides.
Have a crater

25. Mount Fuji

26. 2 Types of eruptions
Explosive: volcanoes that build enough pressure to blow its top, sending pyroclastic material into the air.
Non explosive: Build only enough pressure to allow lava to run down its sides.

27. Pyroclastic materials
Material that is thrown into the air during an explosion.
Volcanic bombs: large blobs of magma that harden in the air.
pebble size rocks
Volcanic ash: tiny powder like material

29. Four types of lava Aa: lava that is thick and sharp
Pahoehoe: lava that forms thin crust and wrinkles
Pillow lava: lava that erupts under water, has a round shape
Blocky lava: cooler, lava that does not travel far from eruption, jagged when it dries.

30. Aa
lava that is thick and sharp

32. Pahoehoe:
lava that forms thin crust and wrinkles

34. Pillow lava
lava that erupts under water, has a round shape

35. Blocky lava
cooler, lava that does not travel far from eruption, jagged when it dries.