15.4: Review and Additional Resources

Review

Review and assess your learning. Start with the "Important Terms and Concepts" to ensure you know the terminology related to the topic of the module and concepts discussed. Move on to the "Review Questions" to answer critical thinking questions about concepts and processes discussed in the module. Finally, test your overall understanding by taking the "Self-assessment quiz".

Important Terms and Concepts

• tectonic plates

  aka lithospheric or crustal plates; make up the surface of the lithosphere

• plate tectonics

  the process of plate formation, movement, and destruction

• continental drift

  the movements of continents over the Earth's surface

• sea-floor spreading

  the creation new oceanic plate material and movement away from the midocean ridge

• Pangea

  the one "super-continent"; the past configuration of the continents

• exotic terrain

  new land that has been formed somewhere else and moved to its present location

• midocean ridge

  the longest continuous mountain system on Earth

• mantle convection currents

  the mechanism that drives continental drift; created by heat trapped beneath the Earth's surface

  

• magnetic reversal

  a series of "flips" when the polarity of the rocks reversed

• subduction zone

  where more dense plates dive beneath lighter, less dense crustal plates

• spreading boundary

  occurs where plates are moving away (diverging) from one another

• convergent boundary

  located where subduction is active and the lithosphere is being "consumed". This occurs where two plates collide with one another

• transform boundary

  where plates are grinding past one another, like the San Andreas fault

• plate boundary zone

  broad belts in which boundaries are not well defined and the effects of plate interaction are unclear

• Ring of fire

  extends from the west coast of the United States toward the Aleutian Islands and over to Japan; a good example of volcano activity associated with the margins of plates

• strain

  change in shape as a result of imposing a stress

• elastic deformation

  Like a rubber band, if the stress is released before reaching the yield point, the rock material will return to its original shape

• brittle failure

  under low temperature and pressure conditions, once the rock reaches its yield point it will break; or if stress is imposed suddenly

• plastic deformation

  once the rock changes shape and if stress is released, it will not return to its original form

• folding

  occurs when rock is compressed, as it is along colliding plate boundaries

• anticline

  Upturned folds

• syncline

  down turned folds

• symmetrical fold

  near-vertical axial planes and gently dipping limbs of about the same angle are a product of gentle compression

• overturned fold

  If the compression is more pronounced from one direction

• recumbent fold

  When extreme directed pressure lay the fold over with its axial plane nearly horizontal with the surface

• fault

  a fracture along which movement occurs

• fault Plane

  The plane that extends into the earth and along which slippage occurs

• fault dip

  the angle from horizontal that the fault plane makes

• strike

  The map direction that the fault takes

• fault scarp

  The steep face of an exposed block

• fault line

  the trace of the fault along the surface

• strike slip fault

  aka transform fault; those that primarily exhibit horizontal movement

• dip slip fault

  those in which vertical displacement primarily occurs

• transform fault

  aka strike slip fault; those that primarily exhibit horizontal movement

• normal fault

  one in which the hanging wall falls down relative to the foot wall due to tensional stress

• reverse fault

  the hanging wall moves up relative to the foot wall due to compression

• graben

  forms when a block of rock falls between two faults

• horst

  forms between two normal faults when a block of rock in the middle remains stationary and the blocks on either side subside

• thrust fault

  a reverse fault at 45^o angle

Review Questions \(\PageIndex{1}\)

What is plate tectonics.

Answer

Plate tectonics is the theory that the surface is broken into several tectonic plates that are moving and interacting with one another to produce relief features of the Earth.

Courtesy USGS

What evidence was used to confirm the notion of continental drift?

Answer

Similar configuration of continents, fossils, and geologic deposits widely separated from one another.

Where does sea flooring spreading occur? How have scienticts confirmed that sea floor spreading is taking place?

Answer

Sea floor spreading occurs along the midocean ridge where new rock material is extruded onto the ocean floor. Magnetic stripes indicate similar polarity in rocks on either side of the ridge. The age of rocks increases away from the midocean ridge.

What drives the movement of tectonic plates?

Answer

It is thought that convection currents in the mantle, the push of crustal rock as it is extruded along the midocean ridge, and the pull of slabs of crust at subduction zones are responsible for the movement of plates.

What is occurring along the midocean ridge?

Answer

The midocean ridge is a primary site for sea floor spreading. As a result, earthquakes and volcanic activity is common.

Sea floor spreading (Courtesy USGS)

What is a subduction zone, where do you find them, and what kinds of geological activity occurs there?

Answer

A subduction zone is where crustal rocks are forced beneath the surface. Subduction is common where heavier, more dense ocean plates collide with lighter, less dense continental plates.

Compare and contrast the four main types of plate boundaries. Give examples of where they occur.

Answer

A spreading boundary occurs where plates are moving away (diverging) from one another, like along the midocean ridge . Here, new crust is formed by accretion. A convergent boundary is found where subduction is active and the lithosphere is being "consumed". A transform boundary forms where plates are grinding past one another, like the San Andreas fault. A plate boundary zone is a broad belts in which boundaries are not well defined and the effects of plate interaction are unclear.

Tectonic Settings (Courtesy USGS)

What is the "Ring of Fire"?

Answer

The "Ring of Fire" is "ring" of volcanoes encircling most of the Pacific ocean.

Ring of Fire (Courtesy USGS)

Describe elastic deformation, brittle failure, and plastic deformation.

Answer

Elastic deformation: when stress is imposed on rock it deformed, when released it returns to its original shape. Brittle failure: breakage caused when stress is imposed beyond the rupture point of brittle materials. Plastic deformation: when stress is imposed on rock it deformed, when released it remains in its deformed shaped.

How does folding occur and what is the result?

Answer

Folding occurs by compression of rock material. An up-turn fold is called an anticline while a down-turn fold is a syncline.

Compare and contrast the different kinds of faults.

Answer

A dip slip fault exhibits vertical displacement. A normal fault is one in which the hanging wall falls down relative to the foot wall due to tensional stress. A reverse fault is one in which the hanging wall moves up relative to the foot wall due to compression. A thrust fault occurs when the hanging wall is pushed up and then over the foot wall at a low angle.

Self-Assessment Quiz \(\PageIndex{1}\)

1. The original "super continent" was called
   1. Pangea
   2. Gondwanaland
   3. Nortreland
   4. none of the above
2. Wegener proposed that continental crust "plowed" through _____ as it moved from one place to the next.
   1. oceanic crust
   2. the mantle
   3. the Moho
   4. none of the above
3. In the late 1920's until the present, the movement of plates is thought to be due to
   1. convection currents in the crust
   2. convection currents in the mantle
   3. convection currents in the core
   4. earthquakes along subduction zones
4. Along the Mid-ocean ridge
   1. earthquakes occur
   2. sea floor spreading occurs
   3. volcanism occurs
   4. all the above occurs
5. Subduction zones are mostly likely found where
   1. ocean crust collides with ocean crust
   2. ocean crust collides with continental crust
   3. continental crust collides with continental crust
   4. where continental crust divergence takes place
6. Which of the following boundaries characterize the San Andreas Fault?
   1. Spreading
   2. Convergent
   3. Transform
   4. None of the above
7. Volcanism in Iceland is due to which of the following plate boundaries?
   1. Spreading
   2. Convergent
   3. Transform
   4. None of the above
8. Volcanism on the Hawaiian Islands is due to which of the following plate boundaries?
   1. Spreading
   2. Convergent
   3. Transform
   4. None of the above
9. The "Ring of Fire" is due to
   1. ocean crust colliding with ocean crust
   2. ocean crust colliding with continental crust
   3. continental crust colliding with continental crust
   4. where continental crust divergence takes place
10. The longest continuous chain of mountains formed by tectonic processes is found
    1. in North America
    2. in South America
    3. in Asia
    4. on the ocean floor

Answer

1. A
2. B
3. B
4. D
5. B
6. C
7. A
8. D
9. B
10. D

Additional Resources

Use these resources to further explore the world of geography

Focus on The Physical Environment: "Earth's Deadliest Earthquakes" (NOVA PBS)

Connections: "South Asia Disaster" News Hour with Jim Lehrer. See "Tsunami Warnings" at the site.

Physical Geography Today: Earthquakes Hazard Program - USGS

Multimedia

San Francisco 1906 Earthquake Science Friday (NPR) April 21, 2006 hour one. "One hundred years ago ..., San Francisco's ground began to shake. After the massive quake came the fire -- and when it was all over, the city lay in ruins, with thousands dead."

"Living with the Earth I" The Earth Revealed (Annenberg/CPB) (30:00) Go to the Earth Revealed site and scroll to "Living with the Earth I". One-time, free registration may be required to view film.

"Exotic Terrane" from the Open Video Project. "A geologic history of the Pacific Northwest that explains how islands near China accreted, or welded, themselves to the North American continent. Animations of the formation of North America explain the process. The video also visits Hells Canyon in Idaho. On-location interviews with an expert geologist add to the viewer's experience". File must be downloaded to view - 245 megabytes

"Faces of Earth: Assembling America" (American Geosciences Institute). "From the Pacific Northwest to the shores of the Atlantic seaboard, the breadth and scope of America is like no other place on Earth. Travel with geoscientists and explore how time and the forces of nature have shaped the continent and influence the life in the United States"

"Southern Appalachians" (USGS) Geology of the Southern Appalachians (24:34)

"The Seattle Earthquake" The News Hour with Jim Lehrer (PBS). A magnitude 6.8 earthquake shook the Pacific Northwest February 28, 2001, rattling windows from Vancouver to Salt Lake City. Read the transcript or watch the clip.

"Earthquakes" Science Friday (NPR) June 24, 2005 episode discusses a recent swarm of earthquakes in California and new studies of the New Madrid Seismic Zone. (17:44)

"Colliding Continents: - Naked Science. How were the continents formed?

Readings

"Plate Tectonics and People" (USGS)

"On the Shoulders of Giants - Alfred Wegener" (NASA)