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Weathering and Soil
Formation
Chapter 10
Mechanical Weathering
Section 1

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

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

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.

Acid in groundwater has
weathered limestone to
form Rusty’s Cave in
Dade County, Georgia.
Acid in groundwater has
weathered limestone to
form Rusty’s Cave in
Dade County, Georgia.
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

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 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
Soil Properties, continued 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.
Chapter 10
Section 3 From Bedrock to Soil
Leaching
Click below to watch the Visual Concept.
Visual Concept
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
surprisin
gly thin
topsoil.
The
salty
conditio
ns of
desert
soils
make it
difficult
for many
plants to
survive.
Soil and Climate, continued
2


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.
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 using
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.