Erosion
and
Deposition
Agents, Forces, and Results
Mrs. Sherry Giarrusso
Palo Alto Science
h"p://commons.wikimedia.org/wiki/
File:Water_erosion_below_Hay_Bluff_-­‐
_geograph.org.uk_-­‐_1074175.jpg h"p://commons.wikimedia.org/wiki/
File:Wind_erosion_Seminole_Canyon.JPG h"p://commons.wikimedia.org/wiki/
File:BavenAan_Clay_Beds_-­‐_geograph.org.uk_-­‐
_1776748.jpg What is Erosion?
•  Erosion – moving
of rock material from one
place to a new location
–
–
–
Three processes must take place:
•
detachment of particles
•
lifting them
•
transporting them
Agents of erosion:
•
flowing water
•
moving ice
•
waves
•
gravity
•
wind
Sand is composed of small pieces of rock that have been:
•
•
•
weathered from a parent rock
eroded
deposited somewhere else
What Is Wind Erosion?
•  Wind – wears away rocks and is responsible for
the creation of deserts such as the Sahara and
the Gobi
- Most effective in moving loose material
–
–
Main effects:
1.
Wind lifts small particles and moves them away.
2.
Suspended particles may cause erosion on solid objects by
abrasion (rubbing).
Occurs in areas where there is not enough rainfall to support vegetation
http://commons.wikimedia.org/wiki/
File:Wind_Erosion_Features_in_Wadi_Al-Hitan.jpg
What Is Water Erosion?
•  Water – most influential force in erosion
–  Moves
materials
–  Transports
–  Wears
large objects with fast moving streams
away rocks:
•  rivers
•  lakes
•  oceans
http://commons.wikimedia.org/wiki/
File:Water_erosion_below_Scarsoch_Bheag__geograph.org.uk_-_1367808.jpg
What Is Wave Erosion?
•
Waves – relentless pounding
•  Erodes:
•
softer/weaker rock first
•
harder/more resistant left behind
•  Can
take over 100 years to erode a rock to sand
•  Energy
of waves and chemicals contained in the water
erode the rock off the coastline.
http://commons.wikimedia.org/wiki/
File:Wave_Erosion,_Downpatrick_Head_-_geograph.org.uk_-
What Is Gravitational Erosion?
•  Mass
Movement
downward movement of
rock and sediments, due primarily to the force
of gravity
–
–  Streams
and glaciers
•  move material from higher é to lower ê elevation
–  Occurs
continuously on all slopes
»  slow moving and sudden movement until equilibrium is
reached
http://commons.wikimedia.org/wiki/
File:Purbeck_,_Old_Harry_-_geograph.org.uk_-
What Is Glacial Erosion?
•
Ice – moves and carries rocks, grinding the
rocks beneath the glacier
–  Plucking
occurs when water enters cracks under the glacier.
•
freezing
•
breaking off pieces of rock that are then carried by the glacier
–  Abrade
(abrasion)
•
cuts into the rock under the glacier
•
smoothing
•
polishing the rock surface
http://commons.wikimedia.org/wiki/File:Ushaped_valley_at_the_head_of_Leh_valley,_Ladakh_(2).JPG
What is Deposition?
•  Deposition – laying down of sediment that has
been transported by a medium such as wind,
water, or ice
–  Process
of erosion stops:
•  when the moving particles fall out of the transporting
medium and settle on a surface
–  Speed of the medium slows or the resistance of the
particles increases, the balance changes and causes
deposition
–  Speed can be reduced by large rocks, hills, vegetation,
etc.
Deposition - Wind
u Wind
speed can be related to variations in
heating and cooling.
u Transportation
of particles in wind:
–  Fine
particles in suspension hundreds of km from its original
source in the desert
–  Heavier
material may be blown along the ground.
–  Material
is deposited when the wind changes direction or loses
its strength.
http://commons.wikimedia.org/wiki/File:Desert_Chihuahuan_Big_Bend.JPG
Deposition - Water
•  Running
water enters a large, fairly still body of
water and its speed decreases
•  SPEED
•
As the speed of the water decreases, the water's ability to carry
sediment also decreases.
•  Deposited
in streams, rivers, and oceans:
•
Running water deposits sediments where the slowing water can
no longer move them.
•
Largest particles are deposited near the shore.
•
Increasingly smaller particles settle out farther from the shore
where the water is calmer.
http://commons.wikimedia.org/wiki/File:Enchanted_Rock,_stream.jpg
Deposition - Ice
•  Glacial
flows of ice
–
become slower when the ice
begins melting
– Deposits left by glaciers:
–  Outwashes
are deposits similar to those left by rivers.
–  Large
chunks of broken rock deposited at the base and sides of the
glacier as it melts and recedes are called Moraines.
–  When
the glacial ice melts, smaller material is carried by the rivers.
http://commons.wikimedia.org/wiki/File:Cavell_Glacier_with_Crevices_and_Annual_Rings.jpg
What’s the Difference?
•
•
•
WEATHERING – Think of weather wearing rock
down.
EROSION – Think of a road and traveling.
DEPOSITION – Think of depositing money into a
bank.