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Weathering and Soil
Formation
Chapter 10
Weathering
 Weathering
is simply the breakdown of
rock into smaller and smaller pieces called
sediment.
 Rocks
on the Earth’s surface are
undergoing weathering all the time, either
by mechanical means or by chemical
means.
Mechanical Weathering
 Mechanical
weathering is simply the
breakdown of rock into smaller pieces by
physical means.
 Agents or causes of mechanical
weathering include:



Ice
Wind
Water
- gravity
- plants
- animals
Agents of Mechanical Weathering
 Explain
how each of the following Causes
mechanical Weathering:




Ice (Define Ice Wedging)
Wind, Water, and Gravity (Define Abrasion)
Plants
Animals
Chapter 10
Weathering
Mechanical Weathering
Ice Wedging
Ice Wedging occurs when water seeps into
cracks of rocks and constantly freezes and
thaws expanding the rock and eventually
breaking it apart
https://www.youtube.com/watch?v=_XnCTcjNpuc
http://my.hrw.com/sh2/sh07_10/student/flash/visual_conce
pts/80127.htm
Mechanical Weathering
Abrasion


http://my.hrw.com/sh2/sh07_1
0/student/flash/visual_concept
s/80130.htm

https://www.youtube.com/watc
h?v=JA4BdLkiRtg
Abrasion: Abrasion
is the grinding and
wearing away of
rock surfaces
through the
mechanical action
of other rock or
sand particles.
Mechanical Weathering

Wind, Water, and Gravity: Wind, water, and gravity
carry rocks, causing them to abrade against one
another.
Mechanical Weathering
(Biological Weathering)
 Plants
As a plant grows, the force of the
expanding root becomes so strong that it
can break a rock apart. (Biological
Weathering)
Animals and Mechanical
Weathering (Biological
Weathering)
Animals that burrow in
the ground break up soil
and loosen rocks to be
exposed to further
weathering (Biological
Weathering)
Chemical Weathering
 Chemical
Weathering is the chemical
breakdown of rocks and minerals into new
substances.
 The most common agents or causes of
chemical weathering are:




Water
Weak Acids
Air
Soil
Agents of Chemical Weathering
 Explain
how each of the following Causes
Chemical Weathering





Water
Acid Precipitation
Acid in Ground Water
Acids in Living Things
Air (Define and explain the result of Oxidation)
Chemical Weathering

Water Even hard rock, such as granite, can be
broken down by water.
Chemical Weathering
(Acid Precipitation)
Sometimes precipitation contains more acid than normal.
Rain, sleet, or snow that contains more acid than normal is
called acid precipitation.

Acid precipitation forms when small amounts of certain
 gases mix with water in the atmosphere.

The gases come from natural sources, such as active
volcanoes.
 They are also produced when people burn fossil fuels,
 such as coal and oil.
Acid Precipitation The high level of acidity in acid
precipitation can cause very rapid weathering of rock.
Chemical Weathering
(Biological Weathering)


Acids in Living Things
Some living things, such
as lichens, produce acids
that can slowly break
down rocks.
https://www.youtube.com/
watch?v=zv2JNaqnYxU&i
ndex=2&list=PLEE924CE
51E2604AD
Lichens, which
consist of fungi and
algae living
together, contribute
to chemical
weathering.
Chemical Weathering

Acids in Groundwater When acidic groundwater comes
into contact with limestone, the limestone is dissolved and
forms karst features.

When the groundwater touches some kinds
 of rock, a chemical reaction happens. The chemical reaction
 dissolves the rock. Over a long period of time, huge
 caves can form where rock has been dissolved.
Acid in groundwater
has weathered
limestone to form
Rusty’s Cave in Dade
County, Georgia.
Chapter 10
Oxidation
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.
http://my.hrw.com/sh2/sh07_10/student/flash/visual_conce
pts/80128.htm
https://www.youtube.com/watch?v=6VnVRHIV6j4
Section 10.2 (Rates of
Weathering)
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.
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.
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
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
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”

Soil Conservation

A method to maintain the fertility of the soil by
protecting the soil from erosion and chemical
decay.
The Importance of Soil

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.
Why is soil Important?


Soil is one of Earth’s most valuable resources
because every thing that lives on land depends
directly or indirectly on soil.
Plants depend directly on the soil to live and
grow.
 Animals depend on plants or on other animals
for food.
 Fertile soil is valuable because there is a limited
supply.
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.
Soil Damage/ Loss

Soil damage can lead to soil loss.

Soil can be damaged from overuse by poor
farming techniques or by overgrazing.

Overused soil can lose its nutrients and become
infertile. Plants can’t grow in soil that is infertile.
Without plants to hold and help cycle water, the
area can become a desert..
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.

Roots from plants and trees are like anchors
to the soil. Roots keep topsoil from being
eroded. Therefore, plants and trees protect
the soil.
What human activities affect soil
erosion?

Farming
 Construction and development
 Mining
What can be done to prevent
soil erosion?





Contour Plowing
Conservation Plowing
Terracing
Windbreaks
Crop Rotation
Contour Plowing and Terracing

Contour Plowing In
contour plowing farmers
plowed rows so that they
run up and down hills.
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. Prevents
erosion from heavy rains
on steep hills
No Till Farming and Cover Crop


No-till farming, which is
the practice of leaving
old stalks, provides
cover from rain. The
cover reduces water
runoff and slows soil
erosion.
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 and Windbreaks

Crop Rotation Farmers
can rotate crops that use
different nutrients so that
nutrients in the soil have
time to become
replenished.

Windbreaks Rows of
trees are planted along
the edges of fields. Block
the wind and also trap
eroding soil.