Weathering
and
Soil
Formation
What is weathering?
 Weathering
is the process by which
rocks are broken down.
– This can be either:
 Physical
 Chemical
Physical a.k.a. Mechanical
Mechanical weathering is the breakdown
of rock into smaller pieces by a physical
means.
For example:

– Wind
– Water
– Gravity
– Ice
– Plants
Ice Wedging

Water seeps into
cracks in rock. Then,
when it freezes it
expands. This causes
the cracks to enlarge.
Ice Wedging
1. Water seeps
into cracks in
rocks.
2. The water freezes
(ice expands). This
causes the cracks to
get larger.
3. The cracks get
so large that the
rock breaks
apart.
Abrasion

The weathering of rocks due to them
rubbing against other rocks or particals.
Wind, Water, Gravity

These are all
ways that
abrasion
occurs.
Plants

Some plants can
easily break
through rocks.
Animals

Burrowing animals such as rats,
earthworms, ants, coyotes, and rabbits
cause a lot of weathering.
Chemical Weathering

Chemical weathering is the process by
which a rock is broken down as a result of
a chemical reaction.
Water
Water is the main ingredient in chemical
weathering.
 It may take thousands of years, but water
can even break down granite.

See the
difference?
1908
1968
Acid Precipitation
Acid precipitation is
any rain, sleet, or
snow that contains
large amounts of
acid.
 All precipitation is
naturally acidic,
however, acid
precipitation
contains more than
normal.

Acid can also be found in
groundwater or in the air.

Oxidation is the chemical reaction that
occurs when elements react with oxygen.
Weathering Review
1.
Give three ways that living organisms can
weather rocks.
2.
How does ice wedging occur?
3.
Give an example of how water can weather
rocks mechanically (physically).
4.
Give an example of how water can weather
rocks chemically.
5.
How does gravity help weather rocks?
Rates
of
Weathering
Rates of Weathering
Hard rocks weather slower than soft rocks.
 This is also called differential weathering.

Devils Tower in Wyoming
What Happened?
Long ago, magma cooled in the center of
a volcano to form igneous rock.
 Over time, the outer rock, softer rock
weathered away leaving only the harder
inner rock.

Devils Tower
Surface Area

Because weathering occurs on the surface
of rocks, the more surface area exposed
to weather the faster a rock will weather.
Warm Up
1.
Explain how climate affects the rate of
chemical weathering.
2. Explain how climate affects the rate of
mechanical weathering.
3. Describe how parent rock is used in the
formation of soil.
Climate affects weathering.

Climate is average weather condition in an
area.
Warm, humid climate
Chemical weathering
occurs faster in warmer,
wetter climates.
 Like Georgia

Water and Temperature

More water and lower temperatures affect
mechanical weathering.

If water freezes and thaws often then ice
wedging occurs more.
Mountain Tops

Mountain tops weather faster because
they are exposed to more wind, rain, and
ice.
From Bedrock
to Soil
What is soil?

Soil is a loose mixture of small mineral
fragments, organic material, water, and
air that can support the growth of
vegetation.
All soil is different

Soil (weathered rock fragments) can be
made of many different types of rock. The
type of rock that the soil was made from
is called parent rock.
Parts of Soil
Bedrock
Bedrock is the layer of rock beneath the
soil.
 Some soil is made from bedrock, so it
remains above the parent rock.

Humus

Humus is the dark, organic material in soil
that is formed from decayed remains of
plants and animals.
Soil Horizons

Soil is usually layered with humus-rich soil
on top, sediment below that, and bedrock
on bottom.
Soil
Conservation
Soil Conservation

Soil Conservation is a method to maintain
the fertility of soil by preventing erosion
and the loss of nutrients.
Importance of soil
Soil provides nutrients to plant life.
 If the soil losses these nutrients then the
plants will not grow.
 All animals get energy from plants.

– How can unhealthy soil effect us?
Housing and Water
Soil is also important to providing shelter
for animals that live in soil.
 It also stores water for plants and animals,
and helps prevent flooding.

Can you tell which is grown in
healthy soil?
Land Degradation

When soil is overused it loses its nutrients.
– This can happen from poor farming
techniques or overgrazing.
Plants can’t grow in infertile soil.
 Without plants and moisture the soil can
be washed or blown away.

Erosion

Erosion is the process by which wind,
water, or gravity transport soil and
sediment from one location to another.

This happens when land is left
unprotected.
This happened in south Georgia long ago.
The result was Providence Canyon.
 What was once cotton fields is now a 150
ft. deep canyon.

Providence Canyon
Providence Canyon
Providence Canyon
Providence Canyon
Providence Canyon
Soil Conservation

There are many ways that farmers help
prevent erosion.
– Contour plowing
– Terracing
– No-till farming
– Cover crops
– Crop rotation
Contour Plowing
Terracing
No-till farming
Cover crops

Cover crops are crops such as soy beans
and peanuts that help restore important
nutrients to the soil.
Crop rotation

Rotating crops from one year to the next.