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Plate Tectonics, Earthquakes, Volcanoes - Study Guide
Section 1 - Inside the Earth (p 88-94)
1. Sketch and label the layers of the Earth. Be sure to include: crust, lithosphere, asthenosphere,
mantle, outer core and inner core.
2. Describe the differences between continental crust and oceanic crust.
Oceanic crust is thinner but more dense, mostly made from basalt, while continental crust is
thicker, less dense and made from rock similar to granite.
3. What are tectonic plates? About how many tectonic plates is Earth’s crust broken up into?
Tectonic plates are pieces of the Earth’s lithosphere that are broken into large sections and move
around on top of the asthenosphere. There about 10-12 major tectonic plates with a couple
smaller sub-plates.
4. How do scientists know about the structure of Earth’s interior?
Scientists know about Earth’s inner structure by studying earthquakes and seismic waves. They
analyzed the various speeds the different seismic waves travel and determined the thickness and
density of Earth’s layers.
Section 2 - Restless Continents (p 95-98)
5. What is Continental Drift and who first wrote this theory?
Continental drift was first proposed by Alfred Wegener and is the theory that the Earth’s
continents have moved in the past, and are constantly moving.
6. What are three pieces of evidence this scientist discovered that supported his theory?
1.
2.
3.
4.
Plant and animal fossil species found across continents.
Similar rock structures/mountain ranges found across continents.
Glacial grooves matching up on different continents.
Puzzle-like fit of the continents.
7. Why did some people not accept this theory at first?
Even though Wegener had a lot of evidence that that continents were once together, he couldn’t
explain how or why the continents are moving, so people doubted him.
8. What other discovery made years later supported the theory of Continental Drift? Describe how this
new discovery and continental drift are connected.
The discovery of the mid-Atlantic ridge and sea-floor spreading helped confirm Wegener’s theory.
Sea-floor spreading is connected to the theory of continental drift because it actually helps
explain why the continents of South America and Africa are getting further apart. As the plates
pull apart new crust is being formed in the middle of the ocean and pushing the continents away
from each other.
9. What is the theory called now?
Continental drift and sea-floor spreading were combined into the Theory of Plate Tectonics.
10. What is Pangaea? When did it exist?
Pangaea is the name of the supercontinent that existed about 200 million years ago.
Section 3 - The Theory of Plate Tectonics (p 99-102)
11. Draw and label a diagram of each of the three main types of plate boundaries. Use arrows to show
direction plate is moving.
a. Convergent Boundaries
b. Divergent boundaries
c. Transform boundaries
12. For each of the boundaries diagramed above, explain what happens at each of these boundaries
and give a real-world example of each one.
a. Convergent boundaries occur when two tectonic boundaries are pushing together.
At oceanic/oceanic and oceanic/continental boundaries the more dense oceanic plate
subducts, destroys crust and volcanoes are formed. Ex. – the Andes Mountains and the
Marianas islands.
At continental/continental convergent boundaries mountains are formed such as the
Himalayas.
b. Divergent boundaries occur when two plates are pulling apart.
At oceanic divergent boundaries mid-ocean ridges (sea-floor spreading) occur and new crust is
created. The mid-Atlantic ridge is an example.
At continental divergent boundaries rift valleys are formed which eventually lead to the land
area filling in with water and new seas are formed. The African rift valley is an example.
c. At transform boundaries the plates are moving sideways past each other and large
earthquakes can occur. The San Andreas fault in CA is an example.
13. Why do tectonic plates move? Explain. About how much do tectonic plates move per year?
Tectonic plates move because convection occurs in the mantle when the mantle material is
heated by the Earth’s core and the material rises towards the crust because warmer objects are
less dense. Once near the surface the mantle material will cool, become more dense and sink
back towards the core. This constant circular movement causes the plates above the
asthenosphere to move at an average rate of 2cm per year.
Section 4 – Deforming the Earth’s Crust (p 103-109)
14. What is the difference between folding and faulting?
Folds are when Earth’s layers bend due to stress. If too much stress is applied, the layers can break and faults
(cracks) in Earth’s crust are created.
Fault –
Fold -
15. What is stress (as it relates to rock layers)?
Stress is the amount of force being put on an object. Stress in Earth’s rock layers occurs because of the
movement of tectonic plates.
16. What are the three main types of mountains and how are they formed?
1. Folded mountains occur when compression squeezes rock layers together.
2. Fault-block mountains form when stress in Earth’s crust cause large blocks of crust to fault and uplift
occurs.
3. Volcanic mountains can occur where subduction zones are at convergent boundaries or can form
above hot spots.
17. What is the relationship between mountain building and Plate Tectonics?
Mountains are formed because Earth’s tectonic plates are continually moving around and bumping into
each other.
18. Complete the table below showing the relationship between types of stress, plate or rock movements and
type of faults that occur.
Type of Stress
Type of Boundary
Type of Fault
(Deformation)
Compression
Convergent
Reverse
Tension
Divergent
Normal
Shear
Transform
Strike-slip
Earthquakes – (Ch. 5)
19. What is an Earthquake?
An earthquake occurs when a sudden release of energy happens when friction builds up at faulst
or tectonic boundaries.
20. What are seismic waves? How are they measured?
The energy from an earthquake travels through the Earth in the form of vibrations called seismic
waves. Seismic waves can be detected and measured by an instrument called a seismograph.
21. What type(s) of plate boundaries do Earthquakes occur? Explain.
Earthquakes can happen at all three types of tectonic boundaries as well as along fault lines or
between faults. Basically, earthquakes can happen anywhere.
Volcanoes – (Ch. 6)
22. How do Volcanoes form?
Volcanoes form at convergent boundaries when oceanic crust is subducted and forced down toward the
mantle where it melts, becomes less dense, and rise back to toward the surface as magma, eventually
erupting from a volcano.
Volcanoes can also form along divergent boundaries when the magma fills in the gap between the
boundaries and cools to create new crust.
Hot spots are areas within plates that magma melts its way through the crust to make volcanoes. The
Hawaiian Islands were formed from a hot spot in the middle of the Pacific Plate.
23. Is there a type plate boundary that volcanoes DO NOT form at? Explain.
Volcanoes do not form at transform boundaries because magma does not make its way to the
surface at those boundaries.
24. What are the three main types of volcanoes? Why are they different?
1. Shield volcanoes are low with gently sloping sides and are formed from layers of lava. Eruptions are
typically non-explosive.
2. Cinder cones are the smallest volcanoes and are cone-shaped. They build from lava that is blown
violently into the air and breaks into fragments. As the lava pieces fall back to the ground, they cool
and harden into cinders that pile up around the volcano’s vent.
3. Composite volcanoes (stratovolcanoes) develop from repeated explosive and nonexplosive eruptions
of pyroclastic material and lava that build up layer by layer. These volcanoes are the largest and form
symmetrical cones with steep sides.
25. What is the Ring of Fire?
The Ring of Fire is the name given the area encircling the Pacific Ocean where many earthquakes
and volcanoes occur to subduction at convergent boundaries.