Erosion and Deposition

Agents, Forces, and Results
•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 consists of small pieces of rock that have been:
• weathered from a parent rock
• eroded
• deposited somewhere else
•Wind – responsible for wearing away rocks and
creating great deserts like the Sahara Desert and Gobi
– Most effective in moving loose material
– 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
•Water – most influential force in erosion
–Moves materials
–Transports large objects with fast moving streams
–Wears away rocks:
• rivers
• lakes
• oceans
•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 chemical content of the water erodes
the rock off the coastline.,_Downpatri
•Mass movement – downward movement of rock
and sediments, mainly due to the force of gravity
–Streams and glaciers
• move material from higher  to lower  elevation
– Occurs continuously on all slopes
» slow moving and sudden movement until equilibrium is reached,_Old_Har
•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,_Ladakh_(2).JPG
•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.
Wind speed can be related to variations in heating
and cooling.
 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
• Running water enters a large, fairly still body of water
and its speed decreases.
• 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.,_stream.jpg
• Glacial flows of ice
– become slower when the ice begins
– Deposits left by glaciers:
– The deposits of these rivers look similar to normal river deposits and are
called 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.
• WEATHERING – Think of weather wearing rock down.
• EROSION – Think of a road and traveling.
• DEPOSITION – Think of depositing money into a bank.