17.4: 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

• weathering

  the breakdown and decomposition of earth material, namely rocks

• physical weathering

  involves the disintegration of rock materials; breaks large pieces into smaller ones

• chemical weathering

  decomposition of rocks and sediment.a chemical change occurs and a new product is created from the material that has undergone weathering

• root wedging

  Plant roots work their way into joints; as they grow, roots create pressure on the sides of the crack enlarging it until the rock breaks apart

• joints

  rock crevices

• frost wedging

  occurs when water freezes in rock fractures. As the water freezes it expands putting pressure on the sides of the crack, enlarging it until the rock breaks apart

• thermal expansion and contraction

  can weaken rock and cause it to disintegrate; expansion upon heating and contraction during cooling weakens rock breaking it apart

• regolith

  the product of weathering

• oxidation

  takes place when oxygen reacts with earth materials. Oxygen dissolved in water combines with atoms of metallic elements abundant in silicate minerals.

• hydrolysis

  an exchange reaction involving minerals and water. Free hydrogen (H⁺) and hydroxide (OH)^- ions in water are able to replace mineral ions and drive them into solution

• karst

   a Yugoslavian term that comes from a narrow strip of limestone plateau noted for the assemblage of solution landforms

• sinkhole

  form either from beneath the surface or from the surface down

• karst window

  forms when the roof above the underground stream collapses in

• mass movement

  the down slope movement of earth materials under the influence of gravity

• shear stress

  primarily a function of the force exerted by the weight of the material under the influence of gravity acting in the down slope direction

• shear strength

  a measure of the resistance of earth materials to being moved

• creep

  occurs in the top few meters of the surface and is accomplished by expansion and contraction of the soil; slowest of all types of mass movement

• slide

  a sheet of material that slips over a failure plane ending anywhere from a meter to a kilometer down slope

• slump

  characterized by a backward rotation of the earth material as it moves along a curved failure plane resulting in a reverse slope

• earth flow

  fairly slow, occurring over a few hours or so slow that they are almost imperceptible. Accompanied with slumping; no backward rotation; are not confined to channels; are more common in humid areas

• mud flow

  is the rapid down slope movement of water-saturated water- saturated soil, regolith. The higher water content creates a flow rapid enough to be perceptible to the eye.  

• rock fall

  occurs when blocks of rock shed from a cliff face and collect at the base

• erosion

  the detachment of earth material from the surface

• rain splash erosion

  caused by the impact of water striking the surface

• sheet erosion

  caused by the unconfined flow of water running across the surface

• rill erosion

  caused by water concentrating into innumerable, closely-spaced small channels

• gully erosion

   steep-sided trenches formed by the coalescence of many rills

Review Questions \(\PageIndex{1}\)

What is the difference between physical and chemical weathering?

Answer

Physical weathering processes are those that break rocks into smaller pieces (disintegration). Chemical weathering chemically alters rock-forming minerals into a product (decomposition).

List the effects of chemical weathering on minerals and rocks.

Answer

• increase bulk creating stress within rocks
• lower the density minerals
• decreased particle size resulting in increased surface area
• creates more mobile materials
• creates more stable minerals

Compare and contrast hydration and hydrolysis as it relates to rock weathering.

Answer

Hydration and hydrolysis involve the absorption of water into the molecular structure of a mineral. Hydration is a reversible process and hydrolysis is not.

What is soil creep and what features of the landscape can be used to tell creep has taken place?

Answer

Soil creep is the slow down slope movement of earth material. The process is imperceptible to the human eye. Terracettes, broken retaining walls, curved tree roots, deformed railroad tracks result from creep.

Compare and contrast slumps and slides.

Answer

Slumps take place on well-defined failure planes, exhibit rotation of the failed mass, and often form terraces. Slides occur along irregular failure planes with the mass sliding down slope burying the overlying surface with debris.

Explain the process of mass movement.

Answer

Mass movement is the down slope movement of earth material under the influence of gravity. Movement occurs when the shearing stress imposed on material is greater than the shearing strength.

What does erosion mean?

Answer

Erosion is the detachment of material from the surface.

Describe the process of rain drop erosion.

Answer

Rain drop erosion occurs in a series of steps. Initial rain drops soak the surface driving soil particles apart. Subsequent rain drops detach soil particles upon impact. A dimpled surface often results from rain splash erosion.

What is particularly harmful about sheet erosion?

Answer

Sheet erosion occurs when the unconfined flow of water across the surface strips thin layers of top soil. It can be imperceptible to the human eye.

Compare and contrast rill and gully erosion.

Answer

Rill erosion occurs when moving water is confined to small channels. A gulley is a much larger channel formed from the coalescence of rills

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

1. Backward rotation of a mass of earth material when mobilized is typical of
   1. slides
   2. slumps
   3. rock fall
   4. creep
2. Another term that describes chemical weathering is
   1. disintegration
   2. decomposition
   3. rotting
   4. fragmentation
3. Curved tree trunks, fractured retaining walls, curved roots are typical features of
   1. slides
   2. slumps
   3. rock fall
   4. creep
4. Talus is a deposit associated with
   1. slides
   2. slumps
   3. rock fall
   4. creep
5. Physical weathering
   1. is typical of warm and wet environments
   2. results in new mineral products being formed
   3. increases surface area
   4. all the above
6. Solifluction is a mass movement process in
   1. the rain forest
   2. the desert
   3. the tundra
   4. the steppe
7. _______ erosion occurs when water is confined to small channels.
   1. rain splash
   2. sheet
   3. rill
   4. gully
8. Sheet erosion
   1. occurs as channeled flow
   2. in some cases is nearly imperceptible
   3. occurs when the infiltration capacity of the soil exceeds the rainfall intensity
   4. all the above
9. Karst landscapes develop over _________ bedrock
   1. sandstone
   2. limestone
   3. granite
   4. basalt
10. Conditions favorable for mudflows include
    1. unconsolidated surface materials
    2. steep slopes abundant but intermittent precipitation
    3. sparse cover of vegetation
    4. all the above

Answer

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

Additional Resources

Use these resources to further explore the world of geography

Focus on The Physical Environment: "Killer Landslides" (NOVA PBS). (29:00)

Connections: When Land Slides (NASA Earth Observatory)

Physical Geography Today: "Real-Time" Monitoring of an Active Landslide above Highway 50, California - USGS

Readings

When Land Slides (NASA EOS)