Erosion and Deposition
Agents, Forces, and Results
What Caused This?
What is Erosion?
• Erosion - moving of rock material from
one place to a new location
– For erosion to occur three processes must
take place: detachment of particles, lifting
them, and transporting them
– Many agents of erosion - flowing water,
moving ice, waves, gravity, or wind
– Sand consists of small pieces of rock that
have been weathered from a parent rock,
eroded, and deposited somewhere else
What Is Wind Erosion?
• Wind - responsible for wearing away rocks and
creating great deserts like the Sahara Desert
and Gobi
– Most effective in moving loose material
– Two main effects: (1) Wind causes small
particles to be lifted and moved away. (2)
Suspended particles may impact on solid
objects causing erosion by abrasion (rubbing).
– Occurs in areas where there is not enough
rainfall to support vegetation
What Is Water Erosion?
• Water - most influential force in erosion
– Ability to move materials from one location to
another over long distances
– The faster water moves in streams the larger
objects it can pick up and transport
– Responsible for wearing away of rocks in
rivers, lakes, and the oceans
What Is Wave Erosion?
• Waves - relentless pounding
– Erodes the softer, weaker parts of the rock
first, leaving harder, more resistant rock
behind
– Can take over 100 years to erode a rock to
sand
– Energy of waves along with the chemical
content of the water erodes the rock off the
coastline
What Is Gravitational Erosion?
• Mass movement - downward movement of
rock and sediments, mainly due to the force of
gravity.
– Moves material from higher elevations to
lower elevations where streams and glaciers
can pick up the material and move it to lower
elevations
– Process is occurring continuously on all
slopes, some act very slowly while others
occur very suddenly until equilibrium is
reached
What Is Glacial Erosion?
• Ice
- moves and carries rocks, grinding the
rocks beneath the glacier
– Glaciers pluck and abrade to cause erosion
– Plucking occurs when water enters cracks
under the glacier, freezing, and breaking off
pieces of rock that are then carried by the
glacier.
– Abrasion cuts into the rock under the glacier,
smoothing and polishing the rock surface
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. This settling is
deposition.
– If the 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
• Wind speed can be related to variations in
heating and cooling
– Wind can transport fine particles in suspension
hundreds of km from its original source in the desert.
– Heavier material may be blown along the ground.
– Material is eventually deposited when the wind
changes direction or loses its strength.
– Obstacles, whether natural of man-made, will often
decide where the deposition occurs and the nature of
the feature formed.
Deposition - Water
• Running water enters a large, fairly still body of
water and its speed decreases.
– As speed decreases, water's ability to carry
sediments decreases
– Sediments carried by running water are deposited
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
– Occurs in streams, rivers, oceans, etc.
Deposition - Ice
• Glacial flows of ice - become slower when the ice
begins melting
– Deposits left by glaciers are called moraines and
outwashes
– Moraines are large chunks of broken rock left at the base
and sides of the glacier as it melts and recedes
– Finer material is carried in the rivers that form when the
glacial ice melts. The deposits of these rivers look similar
to normal river deposits and are called outwashes
What’s the Difference?
• WEATHERING - think weather wearing
rock down
• EROSION - think of a road and traveling
• DEPOSITION – think of depositing money
in a bank