1. Earthquakes, volcanoes, and mountains
4.3 How does the theory of plate tectonics explain Earth’s geological processes?
Earthquakes, volcanoes, and mountains

2. Earthquakes, volcanoes, and mountains are very different, but all result from plate tectonics. Describe how might this theory explain their differences?

3. Almost all earthquakes occur along plate boundaries.
Movement of Earth’s crust can squeeze, stretch, and twist rock. This applies immense pressure.
When the pressure on the rock is applied too quickly or is larger than the strength of the rock, the rock breaks!
The stored energy in the rock is released in the form of an earthquake.

4. How is applying pressure to a stick similar to what is occurring during an earthquake?

5. Earthquake = the natural movement or vibration of the ground that happens when part of the Earth’s crust shifts.
Earthquakes usually occur when rocks suddenly shift along a break in the rock, releasing built-up pressure.
The break where movement happens is call a fault.
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6. There are 3 different types of faults
Reverse
When rock is squeezed together and one block rides up to overlap the other block.
The crust is shortened, horizontally.

7. Normal
When rock is pulled apart and one block slips downward.
The crust is lengthened.

8. Strike-slip
When blocks of rock move past each other horizontally.

9. Earthquake breakdown:
Focus  - the location where an earthquake starts. Usually several kilometers below the surface of the earth.
Epicentre - point on the surface of Earth that is directly above the focus.
Seismic waves - vibrations caused by the release of energy during an earthquake.

10. Seismic Waves

11. Primary Waves
(P waves)
- move the fastest
- are the first ones detected in an earthquake
- cause rock particles to move forward and backward
- can travel through both solids and liquids

12. Secondary Waves (S waves)
- move slower than P waves
- cause rock to move up and down
- can only travel through solids

13. Surface Waves
(L waves)
- are the slowest moving waves
- are on the surface and often cause the greatest damage
- cause rock particles to move both up and down and side to side
- can travel along the surface of Earth and NOT through Earth’s interior

14. Earthquakes are recorded and measured by a seismograph
Earthquakes are recorded and measured by a seismograph. The strength of an earthquakes is then given a number that represents its strength or magnitude. The Richter scale shows the strength of an earthquake using its magnitude.

15. A volcano is anywhere that magma from the mantle reaches Earth’s surface.
Once magma reaches Earth’s surface  it becomes lava.

16. Volcanoes form at convergent plate boundaries in two different ways:
Oceanic-Oceanic
Oceanic-Continental
An oceanic trench forms when the more dense plate subducts beneath the less dense.
Subduction causes magma to rise from the mantle into the upper plate and is released on the surface
Over time the lava builds up to form an island-arc of volcanic islands.
Dense oceanic crust subducts under the continental crust.
Pressure produced by plate colliding causes the crust to fold and crumble, producing mountains
Rising magma due to subduction allows for volcanoes to form along coastal mountain ranges

17. Bc and Volcanoes!
Discuss the ring of fire and its seismic activity

18. Hot spots are unusually hot regions of Earth’s mantle where magma rises to the surface by breaking through weak parts of the lithosphere (crust).
The Hawaiian islands are thought to have formed this way.

19. If volcanic islands are formed from two oceanic plates colliding and volcanic mountain are formed from the collision of an oceanic and continental plate, how do you think massive mountain ranges, such as the Himalayas, are formed?

20. Large mountains are formed from the convergence of two continental plates.
Since they are the same density, there is no subduction
Plates collide causing them to fold and pile up on one another, which results in the formation of mountains.