True or False: The Earth’s surface
has stayed the same for
thousands of years
True or False: The Earth’s surface
has stayed the same for thousands of
years
The Earth’s surface is always
changing!
Weathering
The breakdown of the materials of Earth’s
crust into smaller pieces.
What is Mechanical Weathering?
• Breakdown of rock into smaller pieces
without any change in the chemical
composition of its minerals
– Sometimes called “physical” weathering
– Rock is torn apart by physical force, rather
than by chemical breakdown
– Smaller pieces do not move to a new
location until erosion carries them away
Water causes weathering
What evidence of
weathering do you see
in this picture?
Wind causes weathering
Why wasn’t this mass
of land weathered
away?
What evidence of
weathering do you see
in this picture?
Mechanical - Biotic
• Biotic – means life
– Weathering caused by living organisms
– Plant roots act as a wedge and widen cracks
– Other causes of biotic weathering are digging
animals, microscopic plants and animals,
algae and fungi.
Ice causes weathering
Describe how ice
causes weathering?
Mechanical - Ice Wedging
 Ice Wedging
– Water fills joints of rocks and freezes
– Water expands 10% when it freezes, pushes
rock apart
– Repeated freeze and thaw cycles over the
years causes rock to break along joint
Erosion
The process by which water, ice, wind or
gravity moves fragments of rock and soil.
What evidence of
erosion do you see in
this picture?
What is Chemical Weathering?
• Breakdown of rock into smaller pieces because
of change in the chemical composition of its
minerals
– Chemical reactions break down the bonds holding
the rocks together, causing them to fall apart
– Chemical weathering occurs in all types of rock
– Rock reacts with water, gases and solutions
Chemical - Oxidation
• Oxidation - oxygen combines with other
elements in rocks to form new types of
rock
– New substances are usually much softer than
original, easier for other forces to break rock
apart
– Causes a “rusting” of the rock, often causes a
color change in the rock
Chemical - Carbonation
• Carbonation – Carbon dioxide (CO2) is
dissolved in water making carbonic acid
– Weak acid is formed when CO2 in the air
mixes with rain. This is the same acid found in
soft drinks.
– Acid is too weak to harm plants and animals
but slowly causes feldspars and limestone to
decompose
Erosion is Movement of
Sediment!
• This process, known as
Erosion, is gradually
wearing down the
surface of the earth.
• Erosion is the process
by which weathered rock
and soil (sediment) are
moved from one place
to another.
• Erosion carves the
Earth's surface creating
canyons, gorges, and
even beaches.
What do you think has caused
this rock to look this way?
Wind Erosion
• As the wind blows it picks up
small particles of
sand/sediment and blasts
large rocks with the abrasive
particles, cutting and shaping
the rock.
• The intensity of wind erosion
is determined by:
• Sum (amount)
• Speed
• Slope
• Surface
Wind Erosion
Water Causes Erosion
• runoff, rivers and, streams
Water causes Erosion
When rain falls to the Earth
it can evaporate, sink into
the ground, or flow over
the land as Runoff.
When it flows over land,
erosion occurs.
Runoff picks up pieces of
rock and "runs" downhill
cutting tiny grooves
(called rills) into the land.
Water causes Erosion
How much erosion
takes place is
determined by the:
• Sum (amount)
• Slope
• Speed
• Surface
Can you act increasing
and decreasing the
four S’s?
Ice Causes Erosion
Glaciers wear down the
landscape; by picking up and
carrying debris that moves
across the land along with
the ice.
Ice Causes Erosion
Glaciers can pick up and carry sediment that ranges in size
from sand grains to boulders bigger than houses.
Moving like a conveyor belt and a bulldozer, a single
glacier can move millions of tons of material!
Ice Causes Erosion
How much erosion
takes place is
determined by
the:
• **Sum (Glaciers are
massive!)
• Slope
• Speed
• Surface
Gravity causes erosion
Creep, Slump, Landslides, Mudslides, and Avalanches.
Slower
Faster
These are examples of mass movement
landslide clip.mpeg
(or called mass wasting)
Gravity causes Erosion
How much erosion takes
place is determined by
the:
• Sum
• **Slope
• Speed
• **Surface
Plants CAN CAUSE weathering
Plants CAN PREVENT erosion
Deposition
Rock particles that are picked up and transported
during erosion will ultimately be deposited
somewhere else
Deposition is the process by which sediments (small
particles of rock) are laid down in new locations.
• Together, Erosion and Deposition build new
landforms.
• Deltas
• Canyons
• Meanders
• Floodplains
Delta
Where rivers meet the
ocean is called the
mouth of the river.
Soil and dirt carried
by these rivers is
deposited at the
mouth, and new land
is formed. The new,
soil-rich land is known
as a Delta
Canyons
This simple animation provides
you with a visualization of how the
Colorado River has "downcut"
into the rock layers of the Grand
Canyon.
Canyons are large
valleys created by a
river or stream.
How long it took to carve the
Grand Canyon is debated by
geologists.
Some estimates are between 6
and 8
million years, which is very recent
by comparison.
Meanders
Meandering streams wander side to side as they
constantly seek out the lowest elevation.
This constant motion creates a series of S-shaped
“loops”.
Meanders
Stream Velocity varies from one side to the other side
of the “S”, resulting in erosion in some places and
deposition of sediments in others.
Floodplains
• Floodplains form along
the banks of mid-order
streams and larger rivers.
• These are low-lying
areas along the sides of
a river channel that have
regular times of heavy
waterflow to cause the
river to spill over and
flood the land.