TECTONIC PROCESSES AND LANDFORMS - Discovering Physical Geography - page 368

2. Plate margins can be passive, transform, converging, or
diverging. At diverging plate margins, magma plumes
from the asthenosphere cause rifting, either on conti-
nents or on the seafloor. At converging plate margins,
plates collide or subduct, causing geomorphic features
such as alpine chains and volcanoes.
3. Folding is the process by which rocks are compressed
and deformed. Several kinds of geologic structure are
associated with folded topography, including (a) mono-
clines, (b) synclines, (c) anticlines, (d) overturned folds,
and (e) overthrust faults.
4. Four major kinds of faults occur on Earth: (a) normal, (b) re-
verse, (c) overthrust, and (d) strike-slip faults. Earthquakes

occur when moving plates are stuck along a fault, which
increases stress until a rupture occurs along the fault
plane. The strength of earthquakes is measured on the
logarithmic Richter scale, which indicates the magnitude
of seismic waves passing through the Earth's crust.

5. A volcano is a mountain that erupts periodically when
the buildup of pressure beneath it passes a critical
threshold. Most volcanoes occur along subduction
zones. Three primary kinds of volcanoes occur on
Earth: (a) cinder-cone volcanoes, (b) composite vol-
canoes, and (c) shield volcanoes. The type of volcano
depends on the character of the magma associated
with the system.

C H E C K Y O u R u N D E R S T A N D I N G

1. How does fossil evidence support the theory of conti-
nental drift?
2. How does the age of the Atlantic seafloor support the
theory that the mid-Atlantic plate boundary is a rift?
3. What is the difference between a converging and diverging
plate boundary? Why do diverging plate boundaries occur?
4. How does continental collision cause mountains to
grow? What are the two processes through which alpine
chains evolve?
5. Describe the geologic structure of the Ridge and Val-
ley Province in the Appalachian Mountains. How can it
be that some mountains are underlain by structural syn-
clines, whereas others are underlain by anticlines?
6. Compare and contrast the various kinds of faults on Earth.
7. Discuss earthquake processes, including why they happen,
the nature of seismic waves, and how they are measured.

8. Why are earthquakes typically associated with plate
boundaries?

9. How much stronger is a magnitude 5 earthquake than
a magnitude 2 earthquake?

10. Describe the formation and history of a tsunami that
develops due to an earthquake.

11. Why are volcanoes associated with subduction zones?

12. What are the differences between composite volca-
noes and shield volcanoes?

13. What is the Pacific Ring of Fire, and why does it have
that name?

14. What tectonic feature is associated with Yellowstone
National Park, and what unique features does it con-
tain? In the context of your answer, explain how the mi-
gration of the Yellowstone hotspot fits into the picture.

ANSWERS TO VISUAL CONCEPT CHECKS

V I S U A L C O N C E P T C H E C K 1 3 . 1
The answer is c . The structure shows the limb of an anticline. You can recognize this as an anticline
because the rock structure rises rather steeply.

V I S U A L C O N C E P T C H E C K 1 3 . 2
The answer is d . There is compression of the rocks on either side of the fault. Movement along the fault
produces incredible strain that is causing deformation of the rocks along the fault boundary.

V I S U A L C O N C E P T C H E C K 1 3 . 3
This volcano is a composite volcano, specifically Mount Rainier in Washington. You can tell the nature
of this volcano because it is much too large to be a cinder-cone volcano. It is not a shield volcano
because it is tall with moderately steep sides. Mount Rainier will probably erupt violently because the
magma is highly viscous; thus, a great deal of pressure will build before the eruption occurs.