1. California Standards 3.b.,c. & f.
Chapter 13; Volcanoes

2. Volcanoes are name after the Roman god Vulcan.

3. Formation of Magma
Magma, or liquid rock is formed under three conditions:
When the temperature reaches the melting point of the rock,
when pressure is reduced then the rock will melt and
adding water may decrease the melting point

4. What is volcanism?
Any activity that moves magma or melted rock to the surface of the Earth is called volcanism.
Once magma reaches the Earth’s surface it is then called lava.
The vent through which magma flows is called a volcano.

5. Where does volcanism lie in the rock cycle?
Rocks formed due to volcanism are called igneous rocks.
They are formed by the melting of metamorphic or sedimentary rocks.
Then through cooling and crystallization they become igneous rocks.

6. i
Volcanic Rock = Igneous rock

8. I is for…
Igneous rocks which are formed from volcanoes.
I = Igneous

9. CIRCULATION OF MOLTEN ROCK INSIDE THE EARTH.

10. Igneous Rocks are move to the surface by convection currents.

11. Plate Boundaries
Divergent plate boundary where plates divide or move away from each other.
Convergent plate boundary where plates move together
Transform faults where plates move sideways relative to one another.
Subduction zone where one plate moves below another.

12. Convergent
Divergent

13. Pacific Ocean’s Ring of Fire

14. Hot Spots due to Volcanism
Hot spots are formed away from plate boundaries.
Hot spots form when magma reaches through oceanic crust creating a mid-ocean volcano.
The Hawaii Islands are just such an example.

15. Hot Spots and Hawaii

16. Cracks in the lithosphere

17. Hawaiian Islands and Hot Spots
Direction of plate motion
Hawaiian Islands and Hot Spots

18. Hawaiian Islands
Movement of Pacific Plate

20. Volcanic Eruptions Volcanoes can produce two types of magma:
mafic is dark because of the magnesium and iron so it is dark in color and
felsic is light-colored because of the silicate materials.

21. Volcanic Features

22. Ship Rock National Monument, NM
Plutons

23. VolcanicDikes
Volcanic Dike

24. Other Evidence of Earth’s Heat:
Geysers
Fumeroles
Geothermal springs

26. Types of Volcanoes

27. Volcano Cross Section

29. There are three types of volcanoes:
1. Shield volcanoes which are flat with gently sloping sides.
2. Cinder cone volcanoes with very steep sides made of pyroclastic material
3. Composite or stratovolcanoes volcanoes made up of alternating materials of lava and pyroclastic material.

30. Calderas and Volcanoes
A caldera is formed when a magma chamber collapses and a larger basin is formed.
Caldera are often times filled with water to form a high mountain lake.

31. Caldera; collapsed volcano

32. Crater Lake, Oregon

35. Shield volcano

36. Cinder Cone Volcano

37. Mount St. Helens before eruption of 1980

38. Mount St. Helen during the eruption.

40. Composite Volcano

41. Types of Volcanoes
Shield volcano
Composite Volcano
Cinder Cone

42. Volcano Distribution
There are 18 recognized volcanoes throughout the western United States. Fourteen of them occur from Northern California northward.

43. Island arcs and Volcanoes
When two oceanic plates collide one plate subducts under the other.
This subduction creates an ocean trench.
A string of volcanoes can also be created and is called an island arc.

44. Island Arc

45. The End

46. Volcanic tephra and gases

47. The End

48. Volcano cross section
Volcanic neck