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, lifting of the particles take place: detachment, lifting of the particles and transportand transport

– 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 and have been weathered from a parent rock and 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 to another particles to be lifted and moved to another region. (2) Suspended particles may impact region. (2) Suspended particles may impact on solid objects causing erosion by abrasion.on solid objects causing erosion by abrasion.

– Occurs in areas where there is insufficient Occurs in areas where there is insufficient 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 transporting agents like 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 Bioerosion?• BioerosionBioerosion - erosion of ocean rock by living erosion of ocean rock by living

organisms organisms – Caused by mollusks, polychaete worms, sponges, Caused by mollusks, polychaete worms, sponges,

crustaceans, and fishcrustaceans, and fish– Mechanisms of bioerosion include biotic boring, Mechanisms of bioerosion include biotic boring,

drilling, rasping, and scrapingdrilling, rasping, and scraping– Bioerosion of coral reefs generates fine and white Bioerosion of coral reefs generates fine and white

coral sand. The coral is converted to sand by internal coral sand. The coral is converted to sand by internal bioeroders such as algae, fungi, bacteria, sponges, bioeroders such as algae, fungi, bacteria, sponges, bivalves; external bioeroders include urchins and bivalves; external bioeroders include urchins and chiton.chiton.

– The actions of these organisms cause a great deal of The actions of these organisms cause a great deal of material to be available for erosion.material to be available for erosion.

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

could have been transported by wind, water, or could have been transported by wind, water, or iceice – Process of erosion stops when the transported Process of erosion stops when the transported

particles fall out of the transporting medium particles fall out of the transporting medium and settle on a surfaceand settle on a surface

– Ability to carry material depends on an a Ability to carry material depends on an a balance of forces within the transporting balance of forces within the transporting mediummedium

– If the velocity of the medium reduces or the If the velocity of the medium reduces or the resistance of the particles increases, the resistance of the particles increases, the balance changes and cause deposition.balance changes and cause deposition.

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

Deposition - WindDeposition - Wind• Wind velocity reductions can be related to variations in Wind velocity reductions can be related to variations in

heating and coolingheating and cooling– Wind can transport fine materials in suspension Wind can transport fine materials 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 pulled along the ground.Heavier material may be pulled 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• Stream water enters the lake and its velocity Stream water enters the lake and its velocity

decreases. decreases. – As velocity decreases, water's ability to carry As velocity decreases, water's ability to carry

sediments decreasessediments decreases– Sediments carried by the stream are deposited where Sediments carried by the stream are deposited where

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

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

Deposition - IceDeposition - IceGlacial flows of iceGlacial flows of ice - - become slower if precipitation become slower if precipitation

input is reduced or when the ice begins meltinginput is reduced or when the ice begins melting

– Deposits left by glaciers are called moraines and Deposits left by glaciers are called moraines and outwashes.outwashes.

– Moraines are large chunks of broken rock left at the Moraines are large chunks of broken rock left at the base and sides of the glacier as it melts and recedes.base and sides of the glacier as it melts and recedes.

– Finer material is carried in the rivers that form when Finer material is carried in the rivers that form when the glacial ice melts. The deposits of these rivers look the glacial ice melts. The deposits of these rivers look similar to normal river deposits and are called similar to normal river deposits and are called outwashes. outwashes.

– Glacial rivers are usually white with fine silt known as Glacial rivers are usually white with fine silt known as "glacial milk"."glacial milk".