Forces That Shape Our
Earth:
UNIT 3:
Weathering
And
Erosion
Weathering & Erosion:

Erosion and weathering are major
forces that shape Earth’s surface.

For example, the Grand Canyon
was formed through erosion by the
Colorado River running through it!
What is weathering?
Weathering: The breaking down
of rocks into smaller pieces.
1. Mechanical /Physical
2. Chemical
Hulk
Rock
Smash!
So what is erosion?
Erosion:
The movement
of weathered
rock by wind,
water, glaciers
& gravity
Types of Weathering:
Mechanical/Physical:
Rock is physically broken into smaller
pieces (larger pieces become smaller
pieces of the same rock)
Chemical:
Rock is chemically changed (like
rusting or dissolving away)
5 Agents of Mechanical
Weathering:
1.
2.
3.
4.
5.
Release of Pressure
Freezing & Thawing
Animal Actions
Plant Growth
Abrasion
Release of Pressure
 As
the surface of a rock is
eroded, the rock begins to release
pressure
 Causes top layers of the rock to
crack and flake off
Release of pressure: rock
cracks like an egg shell
Freezing & Thawing
When water in the cracks
of rocks freezes it
expands causing the
crack to enlarge or get
bigger. The ice melts &
refreezes over & over,
breaking the rock apart.
Result of Freezing & Thawing
Animal Actions
Animals
dig (burrow) through
the ground to make their
homes. This loosens the soil &
breaks apart rocks.
Plant Root Growth
Plants roots can grow into
cracks in the rock, slowly
breaking them apart.
Abrasion


Sand and other rock particles in
wind, water or ice can wear
away exposed rock surfaces.
Like sandblasting or sandpaper
on wood
Chemical Weathering
The process that breaks down
the surface of rock by
chemical changes.
1.
2.
3.
4.
5.
5 Agents of Chemical
Weathering
Water
Oxygen
Carbon Dioxide
Living Organisms
Acid Rain
Water
Water
Water
dissolves rock
is the most important
cause of chemical weathering
Oxygen
 Oxygen
+ Water + Iron = Rust
through the Chemical reaction
called Oxidation
 Rock
will become crumbly, soft,
and appear reddish-brown in color
Rusted rock on hillside
Carbon Dioxide
CO2 + rainwater = Carbonic Acid
Carbonic Acid weathers softer rock
like limestone & marble as it seeps
into spaces in rock.
Ex: sinkholes, caves
Living Organisms
The
roots of plants make a
weak acid that slowly
dissolves rocks around the
plant.
Lichens grow on rock
Acid Rain
Acid
rain causes rocks to
weather very rapidly.