1. Please copy your homework into your assignment book
BEFORE THE BELL RINGS
Please copy your homework into your assignment book

2. End Warm-up Name and describe the three types of plate boundaries?
Distinguish between continental crust and oceanic crust.
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End

3. Wednesday, January 11, 2017 Warm-up Review Volcanos and Earthquakes
Work on Midterm Review
Homework: Midterm Exam Review due 1/17

4. Volcanoes

5. A Volcano is…
An opening in Earth’s crust through which molten rock, gases, and ash erupt.
Also, the landform that develops around this opening.

6. Where Volcanoes Form Most volcanoes occur at:
DIVERGENT boundaries, and at
CONVERGENT boundaries that have SUBDUCTION.
Hot Spots

7. Volcanoes at Divergent Boundaries
Decrease in pressure as plates pull apart lets magma rise.
These fissure volcanoes are located at the Mid-Atlantic Ridge and the Great African Rift Valley

8. Volcanoes at Convergent Boundaries (Subduction)
Subduction increases the amount of water in the asthenosphere, which lowers the melting temp.
As the denser oceanic crust is pushed lower, it melts into magma.
When continental and oceanic plates converge, a volcano forms on land.
When 2 oceanic plates converge together, a volcano forms an island.
Mount Hood/ Portland

9. Hot Spots We call these HOT SPOTS.
Sometimes, volcanoes occur at places that aren’t plate boundaries.
We call these HOT SPOTS.
Hot spots are areas where hot magma rises from deep in Earth’s mantle.
Magma escapes where the crust is the thinnest or weakest.
It starts out solid then it melts when it reaches areas of lower pressure.

10. Volcanoes that make up Hawaii.
Example of Hot Spot
Volcanoes that make up Hawaii.

11. Shield Volcanoes Cinder Cone Volcanoes Composite Volcanoes
Types of Volcanoes
There are 4 main types of Volcanoes:
Shield Volcanoes
Cinder Cone Volcanoes
Composite Volcanoes
Fissure Volcanoes

12. Shield Volcanoes
Shield Volcanoes form from runny lava (low viscosity) that tends to flow long distances before hardening. They generally have quiet eruptions.
Volcano has a broad base and gently sloping sides.
Volcano has a less explosive eruption than other types because the lava flows more easily
Type of magma- Mafic Basalt: black, runny lava
Made of layers of lava
Example: Mauna Loa, Hawaii

14. Cinder Cones
Form when molten lava is thrown into the air from a vent. As it falls, it breaks into fragments called ash or tephra that harden before hitting the ground.
The ash and tephra make a cone-shaped mound.
They are smaller than other types.
Erupt explosively because magma is thick, which allows pressure to build up.
Magma composition: Felsic Rhyolite (light colored)

15. Example: Krakatau, Indonesia

16. Cinder Cones
New Guinea
Iceland

17. Composite or Stratovolcano
Form from alternating eruptions of quiet lava and explosive ash. The layers build up and make a moderate-sized volcano.
Most common kind of volcano
Made of layers of ash/tephra and lava.
Magma composition- Andesite: medium color

18. Example of Composite/Stratovolocano
Mt. Pinatubo-Philippines

20. Fissure Volcanoes
Form in long cracks where plates are pulled apart and near other volcanoes where the crust is weakened. Cinder Cone or Shield Volcanoes may also be nearby.

21. How does a Caldera Form? A) A Volcano’s pressure starts to build up
B) The Volcano releases large amounts of Lava
C) As the Lava is released, the pressure decreases and the volcanic mountain begins to collapse, forming a concave shape in the center of the volcano.
D) The center of the volcanic mountain may begin to fill with water and form a lake.

22. Viscosity The hotter the magma or lava, the lower the viscosity.
The viscosity of magma and lava depends on both temperature and composition.
The hotter the magma or lava, the lower the viscosity.
Magmas and lavas high in silica have higher viscosities than magmas and lavas low in silica.

23. Magma
How Magma Forms
Magma is a mixture of molten rock, suspended mineral grains, and dissolved gases that fuels all volcanoes.
Magma forms when temperatures are between 800°C and 1200°C.
Such temperatures exist at the base of the lithosphere and in the asthenosphere.

24. Magma
How Magma Forms
Pressure
Pressure, which increases with depth, is one factor that determines whether rocks will melt to form magma.
As pressure increases, the temperature at which a substance melts also increases.
Due to the effects of pressure, most of the rocks in Earth’s lower crust and upper mantle do not melt to form magma.

25. Magma
Types of Magma
Basaltic Magma
Basaltic magma typically forms when rocks in the upper mantle melt.
Most basaltic magma rises relatively rapidly to Earth’s surface and reacts very little with crustal rocks because of its low viscosity.
The volcanoes fueled by basaltic magma erupt relatively quietly.
Basaltic magma is rich in Iron and Magnesium but low in silica (50%)

27. Magma
Types of Magma
Andesitic Magma
Andesitic magma is found along continental margins, where oceanic crust is subducted into Earth’s mantle, and is formed from oceanic crust or oceanic sediments.
Andesitic magma contains about 60 percent silica, resulting in an intermediate viscosity.
The volcanoes it fuels are said to have intermediate eruptions.

28. Mt. Fuji, Japan
Mt. St. Helens,
Washington State,
USA

29. Magma
Types of Magma
Rhyolitic Magma
Rhyolitic magma forms when molten material rises and mixes with the overlying silica- and water-rich continental crust. (70%+) Silica content.
Rhyolitic magma has high viscosity and fuels very explosive volcanoes.

30. Earthquakes

31. Forces Within Earth What is an Earthquake?
Earthquakes are natural vibrations of the ground caused by movement in Earth’s crust.
In other words:
**When the ground shakes**

32. Forces Within Earth There are 3 kinds of stress acting on rocks:
1. Tension
Compression
Shear

33. Forces Within Earth
Tension -- is stress that pulls a material apart.

34. Forces Within Earth
Compression -- is stress that decreases the volume of a material. It is the force of squeezing together.

35. Forces Within Earth
Shear -- is stress that causes a material to twist or tear.

36. Forces Within Earth Each force creates movement in rock along a fault.
What is a fault?
Faults are cracks or systems of cracks along which movement occurs.

37. Forces Within Earth There are 3 types of faults: Normal Reverse
Strike-slip

38. Forces Within Earth
Normal Faults occur when rocks on one side of the fault drop down as compared to rocks on the other side.
Tension force creates normal faults.
Occur at divergent plate boundaries.
Pulling
FOOTWALL

39. Forces Within Earth Squeezing
HEADWALL
Reverse Faults occur when rocks on one side of the fault are pushed up and over rocks on the other side
Compression force causes reverse faults.
Occur at convergent plate boundaries.

40. Forces Within Earth
Strike–Slip Faults -- occur when rocks on opposite sides of the fault move horizontally past each other.
Shear force causes strike- slip faults.
Occur at transform plate boundaries.

41. Forces Within Earth Earthquakes create 3 types of seismic waves:
Earthquake Waves
Earthquakes create 3 types of seismic waves:
1. Primary waves
2. Secondary waves
3. Surface waves

42. Forces Within Earth
Primary waves or P-waves, squeeze and stretch rocks in the same direction as the waves are traveling.
P-waves are able to travel through anything (solid,liquid,gas).

43. Forces Within Earth
Secondary waves or S- waves, cause rocks to move at right angles to the direction of wave movement.
S-waves are able to travel through solids but not gases or liquids.

44. Forces Within Earth
Surface waves travel along Earth’s surface, moving in two directions as they pass through rock.
Surface waves “roll” like a water wave and cause the most destruction.

45. Forces Within Earth
P-waves and S-waves are also called body waves because they pass through and begin in Earth’s interior.
The point inside the Earth where the first movement of an earthquake occurs is called the focus.
The point on Earth’s surface directly above the focus is called the epicenter.

46. Forces Within Earth
P and S waves begin here