Weathering, Erosion and
Deposition
Weathering
• Weathering is the
wearing away of rock
and can be chemical or
mechanical These
mountains in Costa Rica
were mechanically
weathered by abrasion.
• Abrasion is weathering
by grinding action.
These mountains in Salt Lake City, Utah,
were also weathered by abrasion.
More examples of
weathering on the Pacific
Coast of Costa Rica are
shown by these sea stacks
out in the ocean. They were
formed as ocean waves
weathered away part of the
rocks seen here.
Another example of
how weathering
forms landscapes is
the creation of a
horn. This is a
peak of a mountain
that has been formed
by the weathering
away of rock by
glaciers.
1. Mechanical Weathering
• Process by which rocks are broken down into
smaller pieces by physical forces.
• Types of Mechanical weathering
– Ice wedging
– Plant roots
– Abrasion
– Burrowing of animals (animal action)
– Temperature changes (freezing and thawing)
Frost Wedging
PLANT ROOTS
Abrasion
Animal Action (Burrowing)
How decomposers enrich soil and make it fertile: mechanical weathering.
Chipmunks live
in dens in the
soil and search
the litter for
seeds and nuts.
Plant roots break up
the soil and hold it in
place.
Earthworms
break up the soil,
making it easier
for plant roots to
spread and for
air and water to
enter the soil.
They create
waste which
makes soil more
fertile by adding
nitrogen.
Bacteria are
decomposers
that break down
animal and plant
remains and
wastes.
Freezing and Thawing
(temperature changes)
Chemical Weathering
• the process that breaks down rock through
chemical changes.
• The agents of chemical weathering:
– water- water dissolves rock over time
– oxygen- combines with iron to form rust
(oxidation)
– carbon dioxide- dissolves in water to form
carbonic acid
– living organisms- plant roots secrete acids
– acid rain- from the burning of fossil fuels
Water
• Water weathers rock by dissolving it.
Oxygen
• Iron combines
with oxygen in
the presence of
water in a
processes called
oxidation.
• The product of
oxidation is
rust.
Carbon Dioxide
• CO2 dissolves in
rain water and
creates carbonic
acid.
• Carbonic acid
easily weathers
limestone and
marble.
Living Organisms
• Lichens that grow on rocks produce weak
acids that chemically weather rock.
Acid Rain
• Compounds from burning coal, oil and gas
react chemically with water forming acids.
• Acid rain causes very rapid chemical
weathering.
2 factors that determine the rate of
weathering:
• rock type- Rock that is permeable (has holes
that let water in), weathers faster than rock
that is impermeable. The mineral content of
rock also determines how fast a rock
weathers.
• climate- Rock weathers faster in warm, humid
climates.
Karst Topography
• A type of landscape created by chemical
weathering of limestone
• Located in rainy regions where there is
limestone near the surface, characterized by
sinkholes and caves.
View brainpop animation:
http://www.brainpop.com/science/weather/weathering/
Erosion
• Erosion is the
movement of sediment
by water, wind or ice.
• In this picture taken in
Oregon, a gully has
been created by a
stream that has cut a
path through soft
sediment after a strong
rainfall.
Erosion
• Erosion has caused this
bank in Squaw Creek to
be cut away by the
weathering of the river,
forming a landform that
simulates a partial cave
on the left side of this
picture.
Erosion
• Here, erosion by
longshore drift, has
caused a lagoon to form
along this beach in
Costa Rica.
Mass Movement
• http://www.phschool.com/atschool/phsciexp/
active_art/mass_movement/index.html
Waterfalls
• http://www.classzone.com/books/earth_scien
ce/terc/content/visualizations/es1305/es1305
page01.cfm?chapter_no=visualization
View brainpop video and name 3 types of erosion and how
they change land:
http://www.brainpop.com/science/earthsystem/erosion/
Deposition
•Definition: deposition is
the settling out of sediment
that has been eroded.
Deposition
Deposition is the
adding of sediment in
an area as it settles
out and forms new
landforms. In this
picture, taken in
Squaw Creek, near Sisters, Oregon, rocks have
been deposited along the bank of the river
after heavy rains.
Deposition
• In this picture, also
taken in Squaw
Creek, a sandbar has
been formed by
sediment that has
been washed down
the river. This might
also be considered a
spit.
Deposition
• In this picture, salt has
been deposited in the
Great Salt Lake, Utah.
You can see the salt
deposits. They appear
as white areas on the
edge of the water.
Landforms
• http://www.classzone.com/books/earth_scien
ce/terc/content/visualizations/es1205/es1205
page01.cfm?chapter_no=visualization
Erosion Control Methods:
• These native plants
were left undisturbed
on the beach in Costa
Rica, so that they would
hold in the sand and
prevent erosion on the
beach. This is an
example of permanent
erosion control.
other examples of erosion control:
silt fencing
terracing
River Formation
• A river is a natural stream of freshwater that is
larger than a brook or creek. Rivers are normally
the main channels or largest tributaries of drainage
systems. Typical rivers begin with a flow from
headwater areas made up of small tributaries, such
as springs. They then travel in meandering paths at
various speeds. Finally, they discharge or flow out
into desert basins, into major lakes, or most likely,
into oceans.
Erosion and Deposition
• Meanders are formed
by the weathering of
one bank of a river and
the deposition of the
weathered sediment on
the opposite bank of the
river. This creates a
loop-like bend in a river,
such as this one. This
view was taken from an
airplane over a mountain
range in the midwest.
•changes in a meandering river
• http://www.classzone.com/books/earth_science/t
erc/content/visualizations/es1306/es1306page01.
cfm?chapter_no=visualization
• formation of an oxbow lake:
• http://www.cleo.net.uk/resources/di
splayframe.php?src=309/consultants
_resources%2F_files%2Fmeander4.s
wf
The world's longest river is the Nile River in
Africa, which runs 4,187 miles (6,739
kilometers) from its source in Burundi to the
Mediterranean Sea.
•
• Every river has a point of origin- it is the highest
point in the water basin.
• Gravity- is important; rivers almost always flow
downhill watercourse.
• Some rivers start from springs, especially in humid
climates. Springs occur as groundwater rises to
Earth's surface and flows away.
• Other rivers originate from lakes, marshes, or runoff
from melting glaciers located high in the mountains.
Some rivers have their beginnings in huge glaciers.
Steps to River Formation
1) Precipitation (rainwater or snow ) is the source of the water
for most rivers.
2)When a heavy rain falls on ground that is steeply sloped or is
already saturated with water, water runoff trickles down
Earth's surface rather than being absorbed- this is called
surface runoff.
3) After it travels a short distance, the water begins to run in
small parallel rivulets called rills.
4) As these rills pass over fine soil or silt, they begin to dig
shallow channels, called gullies. This is the first stage of
erosion. A gully only has water in it when it rains.
5) A stream is formed when gullies join together. It is a channel
along which water is continually flowing down a slope.
Streams rarely dry up.
6) A stream grows larger as it gets water from tributaries. A
tributary is a stream that flows into a larger stream.
Visual steps to river formation
Rills
gullies
River System
Notes quiz
1. Examples of mechanical weathering are
a) ice wedging, animal actions, oxidation
b) plant growth, ice wedging, abrasion
c) freezing and thawing, burrowing, acid rain
2. Examples of chemical weathering are
• a) acid rain, oxidation, living organism
• b) freezing and thawing, animal actions, oxidation
• c) burrowing, carbon dioxide, abrasion
3. Deposition is
a) the movement of sediment or rock
b) the settling out of sediment or rock
c) the breaking down of sediment or rock
4. A meander is
• a) a small river that runs into a larger river
• b) a loop-like bend in a river
• c) a lake that has been cut off from a river
•
•
•
•
5) Name 3 methods of erosion control
a)
b)
c)
• 6) What are 2 factors that affect the rate of
weathering?
• a) ______________________
• b) ______________________
• 7) What is surface run-off?
• 8) Rills in soil run together to form __________
that only have water in them when it rains.
•
•
•
•
9) What forms when gullies join together?
a) a rill
b) a stream
c) a tributary
• 10) What is the original source of water of most
rivers? (1st step in river formation)