Chapter 5.1-5.2
Weathering and Soil
What is weathering?
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Weathering is process of breaking down and changing of rock
at or near Earth’s surface.
The two types of weathering are mechanical and chemical
weathering.
What is mechanical weathering?
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Mechanical weathering is the process of physical forces
breaking down rocks into smaller and smaller pieces without
changing the type of rock.
The causes of mechanical weathering are Frost wedging,
Unloading, and Biological activity.
What is frost wedging?
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Frost wedging is a rock break-up caused by the expansion of
freezing water in cracks and crevices.
The broken down pieces are known as talus.
What is unloading?
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Unloading is when large masses of igneous rock are exposed
through uplift, and erosion of over lying rocks.
This reduces the pressure on the rock causing the rock layers
to break away which is known as exfoliation.
What is biological activity?
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Biological activity are the activities of living organisms that
cause the breaking up of rock.
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Roots of trees break rock apart
Burrowing Animals move rocks to the surface where weathering is
more rapid.
Decaying Organisms- produce acid compounds that cause
chemical weathering.
Humans- accelerate mechanical weathering through deforestation
and blasting in search of minerals or in the creation of new roads.
What is chemical weathering?
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Chemical weathering is the process when rock turns
into one or more new compounds.
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Analogy:
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mechanical – tearing paper
chemical – burning paper
Water is the most important agent of chemical
weathering.
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water absorbs gases from the atmosphere and ground.
these dissolved substances chemically react with various
minerals.
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Rust - is iron oxide that forms when iron containing objects are exposed to
water.
Acid rain – is forms when rain absorbs carbon dioxide as it falls. This acid
breaks down rocks.
Spheroidal Weathering
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Chemical weathering can
change both the physical
appearance of rocks as well
as the chemical
composition.
Water enters the joints in
parts of the rocks which then
reshape the rock giving it a
Spherical shape.
What are 3 factors that affect the rate
of weathering?
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Mechanical weathering
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Rock Characteristics
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Breaks rock into smaller pieces, which increasing the surface area
of exposed rocks & accelerates chemical weathering by.
Physical characteristics such as cracks can effect the ability for a
rock to be penetrated.
Mineral composition increase or decrease rate of weathering.
Climate
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controls the frequency of freeze-thaw cycles and affects the rate of
mechanical weathering.
What is Regolith & Soil?
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Weathering produces a
layer of rock and
mineral fragments
called Regolith.
It covers nearly all of
the Earth’s land
surface.
Soil is the part of the
regolith that supports
the growth of plants.
What are the three characteristics of
soil?
The 3 characteristics of regolith are:
 Composition
 Texture
 Structure.
What are the major components of
soil?
 Mineral
Matter
 Organic Matter
(humus)
 Water
 Air
What is soil texture?
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A soil’s texture is the particle size
And the soil’s ability to support plant life.
What is soil structure?
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Soil Structure determines how easily a soil can
be cultivated
And how susceptible it is to erosion.
What causes soil formation?
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Parent material:
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Time:
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The greater the variations in temperature and precipitation, the greater the
influence on the rate, depth, and type of weathering.
Organisms:
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The longer the formation, the thicker the soil.
Climate:
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The source of the mineral matter in soil
Determines the rate of erosion.
Organic matter releases nutrients when it decades and contributes to fertilizing
soil.
Burrowing animals mix the minerals and organic matter in the soil.
Slope:
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Variations of the land can result into different types of soil.
On steep slopes, erosion is accelerated.
Flat areas have little erosion and poor drainage.
What is erosion?
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Erosion is when Earth’s surface is transported by factors such
as water, wind, glaciers, gravity and other agents.
These factors move soil from one place to another.
How do other erosion factors affect
soil?
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When it rains, rain drops strike the soil with force, then the
broken-up particles are carried away by water flowing across
the surface.
Sediment deposition is a natural occurrence that is strongly
influenced by humans, such as land clearing, agriculture,
deforestation, etc.