- View Videolessons: 15 -- Q4R -- Weathering and Soils and
16 -- Mass Wasting.
- Look over the Questions for Reflection
and decide if you would like to use Weathering and Soils as one of your three
Q4R assignments.
- Read Text: Chapter 12, pages 293-312; Chapter 13, pages 313-334.
- Read the Chapter Summaries and Do the Self-Tests below.
I missed a change from the text in the final review for all the geology
sections (1st 8, mid-8, telecourse and military). I attach the corrected
ppfinalreviewoutline03.htm page from the telecourse as an example. I also have
copied the code for the change to Chapter 12 below, it is probably easier for
you just to substitute the code for that one part. Please swap out the material
on all the sites indicated, when you get a chance. Thanks- Debbie
Chapter 12:Weathering and Soils
Weathering
- Weathering refers to the group of destructive processes that change
the physical and chemical character of a rock at or near the earth's surface.
- Weathering breaks down rocks that are either stationary or moving.
Mechanical Weathering
- Mechanical weathering, changes the rock physically- there is little
or no chemical change. Mechanical weathering can increase the rate of
chemical weathering by increasing the surface area exposed to the elements
Chemical Weathering
- Chemical weathering decomposes the rock principally by exposure to
air and water vapor, to form new chemical compounds which are stable in the
surface conditions of the earth.
- The most effective agent of chemical weathering is acid.
Soil Development
- Clay minerals and quartz, two minerals usually remaining after
complete weathering of rock because they are the least reactive, have
important roles in soil development.
- Layers of soil distinguishable by their physical or chemical
characteristics are termed soil horizons.
- The O Horizon is the uppermost layer that consists of nondecomposed
and highly decomposed organic matter.
- The A horizon, forms just below the surface layer of vegetation.
This layer contains decomposed plant material or humus, and contributed to the
leaching in the E Horizon.
- The E horizon or zone of leaching is characterized by a downward
leaching of water.
- The B horizon, or the zone of accumulation, accumulates the
material, often clay, that is leached downward. In humid climates the B
Horizon includes clay, iron oxides and calcite.
- The C horizon is below the B horizon and is the transition between
the unweathered bedrock and the developing soil above.
- Over long periods of time the type of parent rock that produces a soil
becomes less important. Given enough time soils will become quite
similar in the same climate.
Chapter 13: Mass Wasting
When material on a hillside has weathered (the process
described in chapter 5), it is likely to move downslope because of the pull of
gravity. Soil or rock moving in bulk at Earth's surface is called mass wasting.
Mass wasting is one of several surficial processes. Other processes of erosion,
transportation, deposition - involving streams, glaciers, wind, and ocean waves
- are discussed in following chapters.
Landsliding is the best known type of mass wasting. Landslides
destroy towns and kill people. While these disasters involve relatively rapid
movement of debris and rock, mass wasting can also be very slow. Creep is a type
of mass wasting too slow to be called a landslide. In this chapter, we describe
how different types of mass wasting shape the land and alter the environment and
what factors control the rapidity or slowness of the process. Understanding mass
wasting and its possible hazards is particularly important in hilly or
mountainous regions.
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John McNamara
Copyright © 2003 by Debbie Secord. All rights reserved.
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