Exam Date_________
Physics of the Earth
Final Exam Study Guide - Geology
1.
What is tephra?
 Rock fragments thrown into the air during a volcanic eruption
2. What is pyroclastic flow? Why is it SO dangerous?
 Rapidly moving volcanic material.
 Speeds up to 200km/h
 May contain hot, poisonous gases
3. List and describe the three types of volcanoes. What are they made out of?
Shield Volcano
• Broad Gentle Sloping Sides
• Non-Explosive
Composite Volcano
Cinder Cone Volcano
• Alternates Lava and Tephra • Steep sides caused by tephra
• Potentially most dangerous landing around vent
• Explosive
4. Compare and contrast magma and lava.
Magma is molten rock beneath the Earth’s surface
High Temperature: Rocks melt at 800-1200°C
5. Define the following volcano related terms:
a. Vent- an opening in the Earth’s surface in which lava can flow
b. Crater- a great depression formed from the collapse of vent after an eruption
c. Caldera- a caldron like steep depression formed in the side of a volcano after
an explosion
6. What is the difference between an active, dormant, and extinct volcano?
•Active
•Extinct
•Dormant
–Erupts Regularly
–Unlikely to erupt again
–Erupted in past but is now
–Lifetime can span months –No magma/lava supply
quiet
to millions of years
–Ex: Hawaiian Islands not
*Difficult to determine
–Can be currently erupting
over hot spot
status of volcanoes
or showing signs of unrest
(earthquakes, emitting gas)
–Ex: Mt. St. Helens
7. What are hotspots? (Give an example)
Hot Spots are unusually hot regions of Earth’s mantle where plumes
of magma rise to surface
Located away from plate boundaries Example: Hawaii
8. If volcano A is further from a hotspot than volcano B, which volcano is older?
Volcano A is further from the hotspot.
Volcano A is older.
9. What is viscosity?
Viscosity is the internal resistance to flow
•Low Viscosity – Moves fast (Less thick)
•High Viscosity – Moves slow (More thick)
10. How do P waves move?
P-Waves squeeze and pull rocks in the same direction as the wave travels
11. How do S waves move?
S-Waves cause rocks to move at right angles to the direction of the wave
12. How do surface waves move?
Surface Waves move rocks up and down, as well as side-to-side
Motion is similar to an ocean wave
13. What is an earthquakes epicenter?
The Epicenter is the point on Earth’s surface directly above the focus
14. What is an earthquakes focus?
Earthquakes originate at a point
Focus is usually below the surface
15. In what order do seismic waves arrive at a seismograph?
P-Waves
S-Waves
Surface Waves
16. What are the steps for locating an earthquake’s epicenter? How many locations with data
do you need to determine the epicenter?
Epicenters are located by the separation between S- and P-waves on a
seismogram
Cannot use one location to map epicenter
Need to use three or more seismic stations
Time can be measured in same way
Three locations should meet at the epicenter
17. List and describe the three types of faults.
Reverse Faults are fractures that result from horizontal compression
Shortens crust horizontally
Normal Faults are fractures caused by horizontal tension
Lengthens crust horizontally
Strike-Slip Faults are fractures caused by horizontal shear
Motion is mainly horizontal
18. Describe shearing forces.
Shear is stress that causes a material to twist
19. Describe compression forces.
Compression is stress that decreases the volume of material
20. Describe tension forces.
Tension is stress that pulls a material apart
21. What is a seismic gap?
Segment of an active fault that has not slipped in an unusually long time
when compared with other segments along the same structure.
22. List and describe the scales used to measure earthquakes.
Moment Magnitude Scale includes:
Size of fault rupture
Amount of movement along fault
Rocks’ stiffness
Modified Mercalli Scale assesses damage from a quake

Richter Scale is based on the largest waves generated by the quake
23. What is a tsunami?
A large wave of water caused by an underwater earthquake
24. What is the theory of continental drift? Who developed this theory?
Hypothesis that Earth’s continents were joined as a single landmass that
broke apart about 200 mya (million years ago) and slowly moved to their
present locations
Alfred Wegener
25. What evidence was there for continental drift? Explain.
Fossils-Similar fossils of several different plants and animals that once
lived near each other found on widely separated continents
Land animals did not swim across ocean
Rock Formations- Rock types found in Appalachian Mountains similar to
those found in Greenland and Europe
Climatic Evidence- Coal deposits in Antarctica indicate that the climate
was much warmer in the past
Must have been located closer to the equator before it drifted
26. What were the flaws of continental drift? Explain.
Not able to explain what force was large enough to move such large
pieces of earth over a great distance
Not able to explain how the ocean basins were not shattered, move
through solids