Weathering and Soil
Formation
Chapter 10
Old and New Mountains

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The Appalachian
Mountains appear very
different from the Sierra
Mountains.
The Appalachians are
smaller, rounded, gently
sloping, and covered
with plants.
The Sierras are twice as
high, and very rocky and
steep.
The Appalachians are
much older so they have
had more time to
weather and erode.
Weathering

The natural processes
that break down
exposed rock and turns
it into soil.
 Heat, cold, water, and
ice, and wind all can
weather rock.
 Rocks get weathered
into smaller and
smaller pieces,
forming the basis of
soil.
Mechanical Weathering
Section 1

Mechanical (physical)
weathering is when rock is
physically broken into smaller
pieces.

Ice: The alternate freezing and
thawing of soil and rock, called
frost action, is a form of
mechanical weathering.

Abrasion: Abrasion is the
grinding and wearing away of rock
surfaces through the mechanical
action of other rock or sand
particles.

Wind, Water, and Gravity: Wind,
water, and gravity carry rocks,
causing them to abrade against
one another.
Chapter 10
Section 1 Weathering
Ice Wedging
Click below to watch the Visual Concept.
Visual Concept
Mechanical Weathering, continued 2
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Plants As a plant grows, the force of the expanding root
becomes so strong that it can break a rock apart.

Animals Almost any animal that burrows causes
mechanical weathering by mixing and digging through
soil and rock particles.
Animals and Mechanical
Weathering

Animals that burrow
in the ground break
up soil and loosen
rocks to be exposed
to further weathering.
Chemical Weathering
Acid in groundwater
has weathered
limestone to form
Rusty’s Cave in Dade
County, Georgia.

Water Even hard rock,
such as granite, can be
broken down by water. The
next slide shows how this
can happen.

Acid Precipitation The
high level of acidity in acid
precipitation can cause
very rapid weathering of
rock.

Acids in Groundwater
When acidic groundwater
comes into contact with
limestone, the limestone is
dissolved and forms karst
features.
Chemical weathering:
the process by which
rocks break down as a
result of chemical
reactions. A new
substance is created.
Chemical Weathering of Granite
Chemical Weathering, continued
2

Acids in Living Things
Some living things, such
as lichens, produce acids
that can slowly break
down rocks.

Air Oxygen in the air
causes oxidation.
Oxidation is the chemical
reaction in which an
element, such as iron,
combines with oxygen to
form an oxide.
Lichens, which
consist of fungi and
algae living
together, contribute
to chemical
weathering.
Chapter 10
Section 1 Weathering
Oxidation
Click below to watch the Visual Concept.
Visual Concept
Differential Weathering
Section 2

What Is Differential Weathering? Differential
weathering is a process by which softer, less
weather resistant rock wear away and leave
harder, more weather resistant rock. The image
below is an example of differential weathering.
The Shape of Rocks

Surface Area The more
surface area of a rock
that is exposed to
weathering, the faster the
rock will be worn down.

Increasing the Rate of
Weathering If a large
rock is broken down into
smaller fragments,
weathering of the rock
happens much more
quickly.
Surface Area and Volume
Weathering and Climate

What Is Climate? Climate is the average weather
condition in an area over a long period of time.

Temperature and Water The rate of chemical
weathering happens faster in warm, humid climates.
Water also increases the rate of mechanical weathering.
Weathering and Elevation

High Elevations Rocks
at higher elevations, as
on a mountain, are
exposed to more wind,
rain, and ice than rocks at
lower elevations.

Steep Slopes The
steepness of mountain
slopes increases the
effects of mechanical and
chemical weathering.
Steep slopes cause water
and sediments to quickly
run down the side of the
mountain.
The Source of Soil
Section 3
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What Is Soil? Soil is a loose mixture of small mineral fragments,
organic material, water, and air that can support the growth of
vegetation.
Residual and Transported Soil: Soil that remains above its parent
rock is called residual soil. Soil that is blown or washed away from
its parent rock is called transported soil.
Chapter 10
Section 3 From Bedrock to Soil
Residual and Transported Soil
Click below to watch the Visual Concept.
Visual Concept
Soil
Ch. 11
Loam
Loam, a type of very
fertile soil is made
up of air, water and
organic materials as
well as minerals from
weathered rock.
 Rich fertile soil that
is made up of about
equal parts of clay
sand and silt.

Soil Properties
• Soil Texture and
Soil Structure Soil
texture is the soil
quality that is based
on the proportions of
soil particles. Soil
structure is the
arrangement of soil
particles.
Transported soil may be
moved long distances from
its parent rock by rivers,
such as this one.
Soil Texture
Gravel
Soil Properties 2

Soil Fertility A soil’s
ability to hold nutrients
and to supply nutrients
to a plant is described
as soil fertility.

Soil Horizons Because
of the way soil forms,
soil often ends up in a
series of layers called
horizons.

Soil pH Soils can be
acidic or basic. The pH
scale is used to
measure how acidic or
basic a soil is.
Soil Layers
Chapter 10
Section 3 From Bedrock to Soil
Leaching
Click below to watch the Visual Concept.
Visual Concept
Regolith
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
A term that
describes the
weathered material
that is on top of the
bed rock
Top soil is the top
layer of regolith
Regolith protects
the rock below from
weathering because
bedrock weathers
easier than regular
rock
Soil Triangle
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A soil texture triangle is used
to classify the texture of a
soil.
The sides of the soil texture
triangle are scaled for the
percentages of sand, silt, and
clay.
Clay percentages are read
from left to right across the
triangle
Silt is read from the upper
right to lower left
Sand from lower right
towards the upper left portion
of the triangle
. The intersection of the
three sizes on the triangle
give the texture class. For
instance, if you have a soil
with 20% clay, 60% silt, and
20% sand it falls in the "silt
loam" class.
Soil and Climate


Tropical Rain Forest
Climates The warm soil
in tropical rain forest
climates allows dead
plants and animals to
decay easily. This
provides rich humus to
the soil.
Desert Climates The
lack of rain in desert
climates leads to low
rates of chemical and
mechanical weathering.
Lush tropical
rain forests
have
surprisingly
thin topsoil.
The salty
conditions
of desert
soils make it
difficult for
many plants
to survive.
Soil and Climate 2
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Temperate Forest and
Grassland Climates
Temperate forest and
grassland climates get
enough rain to cause a high
level of chemical
weathering, but not too
much that nutrients are
leached out.
Arctic Climates In arctic
climates, as in desert
climates, chemical
weathering occurs very
slowly. Low temperatures
slow the formation of
humus.
The rich
soils in
areas that
have a
temperate
climate
support a
vast
farming
industry.
Arctic soils,
such as the
soil along
Denali
Highway, in
Alaska,
cannot
support
lush
vegetation.
The Importance of Soil
Section 4

Nutrients Soil provides
minerals and other
nutrients for plants. All
animals get their energy
from plants.

Housing Soil provides a
place for animals to live.

Water Storage Without
soil to hold water, plants
would not get the
moisture or the nutrients
they need.
Soil Damage and Loss

Overuse Overused soil can lose its nutrients and
become infertile.

Soil Erosion When soil is left unprotected, it can be
exposed to erosion. Erosion is the process by which
wind, water, or gravity transport soil and sediment from
one location to another.
Providence
Canyon,
Georgia,
shows the
effects of
cutting
forests for
farm land.
Providence Canyon
Providence
Canyon is near
Lumpkin,
Georgia. It has
beautiful gullies
formed by
erosion 150
years ago. This
park is part of
Georgia's East
Gulf Coastal
Plain region.
People call it
Georgia's "Little
Grand
Canyon." There
are 16 canyons
altogether. Some
canyons are 1
mile long and 300
feet across. An
ancient ocean
formed all the
canyons.
Georgia Red Clay

Georgia is famous for
its red clay.
 This red color comes
from the high iron
content in the soil.
 Think rust!
Dust Bowl
In the 1800’s settlers in the
Great Plains turned the
fertile, moisture laden sod
into farmland.
 In drought, this land dried
up and blew away as dust.
 In the 1930’s, severe
drought over several years
allowed this soil to be blown
away in great, dark clouds.
 Some of these dust storms
reached New York City.
 This lasted until 1938.
Many farmers in the “Dust
Bowl” had to abandon their
homes and move away.
 Read Steinbeck’s “The
Grapes of Wrath”

Contour Plowing and Terracing

Contour Plowing In
contour plowing, the rows
of soil act as a series of
dams to prevent water
from eroding topsoil
away.

Terracing If hills are
steep, farmers can use
terracing. Terracing
changes one steep field
into a series of smaller,
flatter fields.
Cover Crop and Crop Rotation

Cover Crops Cover
crops are crops that are
planted between harvests
to replace certain
nutrients and prevent
erosion. Cover crops
prevent erosion by
providing cover from wind
and rain.

Crop Rotation Farmers
can rotate crops that use
different nutrients so that
nutrients in the soil have
time to become
replenished.