Erosion and DepositionErosion and Deposition

Agents, Forces, and ResultsAgents, Forces, and Results

What Caused This?What Caused This?

What is Erosion?What is Erosion?• Erosion - Erosion - moving of rock material from moving of rock material from

one place to a new locationone place to a new location– For erosion to occur three processes must For erosion to occur three processes must

take place: detachment of particles, lifting take place: detachment of particles, lifting them, and transporting themthem, and transporting them

– Many agents of erosion - flowing water, Many agents of erosion - flowing water, moving ice, waves, gravity, or windmoving ice, waves, gravity, or wind

– Sand consists of small pieces of rock that Sand consists of small pieces of rock that have been weathered from a parent rock, have been weathered from a parent rock, eroded, and deposited somewhere elseeroded, and deposited somewhere else

What Is Wind Erosion?What Is Wind Erosion?• WindWind - - responsible for wearing away rocks and responsible for wearing away rocks and

creating great deserts like the Sahara Desert creating great deserts like the Sahara Desert and Gobiand Gobi– Most effective in moving loose materialMost effective in moving loose material – Two main effects: (1) Wind causes small Two main effects: (1) Wind causes small

particles to be lifted and moved away. (2) particles to be lifted and moved away. (2) Suspended particles may impact on solid Suspended particles may impact on solid objects causing erosion by abrasion (rubbing).objects causing erosion by abrasion (rubbing).

– Occurs in areas where there is not enough Occurs in areas where there is not enough rainfall to support vegetationrainfall to support vegetation

What Is Water Erosion?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?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?What Is Glacial Erosion?• IceIce - - moves and carries rocks, grinding the moves and carries rocks, grinding the

rocks beneath the glacierrocks beneath the glacier– Glaciers pluck and abrade to cause erosionGlaciers pluck and abrade to cause erosion– Plucking occurs when water enters cracks Plucking occurs when water enters cracks

under the glacier, freezing, and breaking off under the glacier, freezing, and breaking off pieces of rock that are then carried by the pieces of rock that are then carried by the glacier. glacier.

– Abrasion cuts into the rock under the glacier, Abrasion cuts into the rock under the glacier, smoothing and polishing the rock surfacesmoothing and polishing the rock surface

What is Deposition?What is Deposition?• Deposition Deposition -- laying down of sediment that has laying down of sediment that has

been transported by a medium such as wind, been transported by a medium such as wind, water, or icewater, or ice – Process of erosion stops when the moving Process of erosion stops when the moving

particles fall out of the transporting medium particles fall out of the transporting medium and settle on a surface. This settling is and settle on a surface. This settling is deposition.deposition.

– If the speed of the medium slows or the If the speed of the medium slows or the resistance of the particles increases, the resistance of the particles increases, the balance changes and causes deposition.balance changes and causes deposition.

– Speed can be reduced by large rocks, hills, Speed can be reduced by large rocks, hills, vegetation, etc. vegetation, etc.

Deposition - WindDeposition - Wind• Wind speed can be related to variations in Wind speed can be related to variations in

heating and coolingheating and cooling– Wind can transport fine particles in suspension Wind can transport fine particles in suspension

hundreds of km from its original source in the desert. hundreds of km from its original source in the desert. – Heavier material may be blown along the ground.Heavier material may be blown along the ground.– Material is eventually deposited when the wind Material is eventually deposited when the wind

changes direction or loses its strength.changes direction or loses its strength.– Obstacles, whether natural of man-made, will often Obstacles, whether natural of man-made, will often

decide where the deposition occurs and the nature of decide where the deposition occurs and the nature of the feature formed.the feature formed.

Deposition - WaterDeposition - Water• Running water enters a large, fairly still body of Running water enters a large, fairly still body of

water and its speed decreases. water and its speed decreases. – As speed decreases, water's ability to carry As speed decreases, water's ability to carry

sediments decreasessediments decreases– Sediments carried by running water are deposited Sediments carried by running water are deposited

where the slowing water can no longer move them. where the slowing water can no longer move them. Largest particles are deposited near the shore. Largest particles are deposited near the shore. Increasingly smaller particles settle out farther from Increasingly smaller particles settle out farther from the shore where the water is calmerthe shore where the water is calmer

– Occurs in streams, rivers, oceans, etc. Occurs in streams, rivers, oceans, etc.

Deposition - IceDeposition - Ice• Glacial flows of iceGlacial flows of ice - - become slower when the ice become slower when the ice

begins meltingbegins melting

– – Deposits left by glaciers are called moraines and Deposits left by glaciers are called moraines and outwashesoutwashes– – Moraines are large chunks of broken rock left at the baseMoraines are large chunks of broken rock left at the base and sides of the glacier as it melts and recedesand sides of the glacier as it melts and recedes– Finer material is carried in the rivers that form when the Finer material is carried in the rivers that form when the

glacial ice melts. The deposits of these rivers look similar glacial ice melts. The deposits of these rivers look similar to normal river deposits and are called outwashes 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