Mass Wasting - The Changing Earth: Exploring Geology and Evolution - page 297

Mudfl ows consist of mostly clay- and silt-sized particles
and contain up to 30% water. They are most common
in semiarid and arid environments, and generally follow
preexisting channels.
Debris fl ows are composed of larger particles and contain
less water than mudfl ows.
Earthfl ows move more slowly than either debris fl ows
or mudfl ows, and move downslope as thick, viscous,
tongue-shaped masses of wet regolith.
Quick clays are clays that spontaneously liquefy and fl ow
like water when they are disturbed.
Solifl uction is the slow downslope movement of water-
saturated surface material and is most common in areas
of permafrost.

Creep, the slowest type of fl ow, is the imperceptible
downslope movement of soil or rock. It is the most wide-
spread of all types of mass wasting.
Complex movements are combinations of different types
of mass movements in which no single type is dominant.
Most complex movements involve sliding and fl owing.
The most important factor in reducing or eliminating the
damaging effects of mass wasting is a thorough geologic
investigation to outline areas susceptible to mass movements.
Although mass movement cannot be eliminated, its
effects can be minimized by building retaining walls,
draining excess water, regrading slopes, and planting
vegetation.

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Important Terms

complex movement (p. 290)
creep (p. 289)
debris fl ow (p. 287)
earthfl ow (p. 287)
mass wasting (p. 274)
mudfl ow (p. 286)

permafrost (p. 289)
quick clay (p. 287)
rapid mass movement (p. 278)
rock slide (p. 281)
rockfall (p. 278)
shear strength (p. 274)

slide (p. 279)
slow mass movement (p. 278)
slump (p. 280)
solifl uction (p. 289)

Review Questions

1. Shear strength includes
a. _____ the strength and cohesion of material;
b. _____ the amount of internal friction between
grains;
c. _____ gravity;
d. _____ all of these;
e. _____ answers a and b.
2. Downslope movement of material along a more or less
planar surface is a(n)
a. _____ slump;
b. _____ rockfall;
c. _____ earthfl ow;
d. _____ debris fl ow;
e. _____ rock slide.
3. The most widespread and costly of all mass wasting
processes is
a. _____ slumps;
b. _____ creep;
c. _____ mudfl ows;
d. _____ rockfalls;
e. _____ quick clays.

4. Which of the following factors can actually enhance
slope stability?
a. _____ increasing the slope angle;
b. _____ vegetation;
c. _____ overloading;
d. _____ rocks dipping in the same direction as the
slope;
e. _____ none of these.
5. Which of the following are the most fl uid of mass
movements?
a. _____ earthfl ows;
b. _____ mudfl ows;
c. _____ debris fl ows;
d. _____ slumps;
e. _____ solifl uction.
6. Mass wasting can occur
a. _____ on gentle slopes;
b. _____ on steep slopes;
c. _____ in fl at-lying areas;
d. _____ all of these;
e. _____ none of these.