Deposition, Weathering, and

Erosion

Weathering

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What Caused This?

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Effects of Weathering

• Weathering is a process that breaks down rock and other substances at Earth’s surface– creates soil– softer rock weathers faster– weathering is fastest in hot and wet

climates

Types of Weathering

• Mechanical Weathering• Chemical Weathering

What is Mechanical Weathering?

• Breakdown of rock into smaller pieces without any change in the chemical composition of its minerals.– Sometimes called “physical” weathering– Rock is torn apart by physical force, rather

than by chemical breakdown.

Mechanical Weathering

• Works very slowly• There are different types

– ice wedging– exfoliation– thermal– biotic

Mechanical - Ice Wedging Ice Wedging

– Water fills joints of rocks and freezes– Freezing expands the water by 10%–Repeated freeze and thaw cycles

over the years causes rock to break along joint

Mechanical - Exfoliation• Exfoliation or unloading

–Rock breaks off into leaves or sheets along joints which are parallel to the ground surface

Mechanical - Thermal • Thermal expansion

– Repeated daily heating and cooling of rock –Different minerals expand and

contract at different rates causing the rock to split

Mechanical - Biotic• Biotic – means life

–Weathering caused by living organisms

– Plant roots, digging animals, microscopic plants and animals, algae and fungi.

Mechanical Weathering

What is Chemical Weathering?• Breakdown of rock into smaller pieces

because of change in the chemical composition of its minerals.– Chemical reactions break down the bonds

holding the rocks together, causing them to fall apart.

– Chemical weathering occurs in all types of rock but smaller rocks are more susceptible because they have a greater amount of surface area.

Chemical Weathering

• Types of chemical weathering• Oxidation (oxygen)• Hydrolysis (water)• Carbonation (carbon dioxide)• Biotic (living organisms)• Acid rain

Chemical - Oxidation• Oxidation - oxygen combines with

other elements in rocks to form new types of rock. – Causes a “rusting” of the rock, often

causes a color change in the rock

Chemical - Hydrolysis• Hydrolysis - water combines with the

substances in rocks to form new types of rock– New substances are softer than the

original rock types

Chemical - Carbonation• Carbonation – Carbon dioxide is

dissolved in water making carbonic acid, which eats away at the rock– Weak acid is formed when carbon dioxide

in the air mixes with rain. This is the same acid found in soft drinks. 

Chemical - Biotic• Organisms - living organisms can cause

changes in the chemistry of rock– Plants lower the local pH to make it more

acidic– Bacteria act as catalysts in various

geochemical processes

Chemical Weathering

Weathering by Water

• Most important agent of chemical weathering• It can dissolve rock and minerals in rock

Weathering by Waves

• Waves weather the land:– Mechanical weathering

• Broken down into smaller pieces

– Chemical weathering• Dissolved in water

Weathering by Waves

Weathering by Wind

• Wind weathers the land by mechanical means– Abrasion

• Very slow process

Weathering by Wind

weathering

The breaking down of rock into smaller pieces that remain next to each other. Weathering forms sediments

ice wedging

mechanical weathering chemical weathering

Physical breaking of rock without any change in the chemical composition of the rock.

The breaking down of rock into smaller pieces because of chemical changes within the rock.

hydrolysis carbonation

biotic

thermal

biotic force oxidation

exfoliation

Erosion

What Caused This?

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Erosion

• Movement of weathered rock and soil to a new location. – gravity– water– glaciers– waves– wind

What Is Gravitational Erosion?• downward movement of rock and

sediments, mainly due to the force of gravity.

Erosion by Gravity

• Gravity can erode landscapes– Landslides – Mudflow– Slump – Creep

Erosion by Water

• Moving water is the strongest agent of erosion that has shaped Earth’s land surface

• Erosion by water starts with rain. As the rain runs downhill, it carries soil rock and other material with it

Erosion by Water

• The rate depends on amount of rain, vegetation, type of soil, shape of land, and how people use the land

• As water moves fast, it picks up sediment

• As water slows down, it drops sediment

Water

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

rocks beneath the glacier– Glaciers pluck and abrade to cause erosion

Erosion by Glaciers

What Is Wave Erosion?• Waves - relentless pounding of waves that

erodes the weaker, softer rock – Can take over 100 years to erode a rock to

sand

Erosion by Waves

• When waves hit rocky coastlines, the impact can break off pieces of the rock

• The sand and sediment in the waves can also act like sandpaper and wear away rock

Waves

What Is Wind Erosion?• wind picks up surface material and

moves it, weakest agent of erosion– responsible for creating great deserts like the

Sahara Desert and Gobi

Wind

erosion

Movement of sediments from one place to another.

wind

gravity

waves

water

glaciers

Deposition

Deposition• laying down (dropping) of

sediment carried by wind, water, or ice

Deposition by Water

• Water is the strongest agent of deposition.

• Rivers deposit soil and sediment on their flood plains and deltas

• Good farmland is usually based on land where sediment was deposited by water

Water Deposition

Deposition by Water

Deposition by Glaciers

• When a glacier melts, it deposits the sediment it eroded from the land

• This deposition can create new landforms and deposit sediment in new areas–Till – material deposited on the land’s

surface–Moraine – ridge at the edge of a

glacier

Glacier Deposition

Deposition by Waves

• Waves shape coastlines by depositing sand on the beach

• The type of sand is determined by the sediment on the ocean floor– White sand– Black sand

Deposition by Waves

Deposition by Wind

• Wind is the weakest agent of deposition

• When it drops the sediment it is carrying, it can form dunes or mounds

Deposition by Wind

deposition

Laying down of sediment that was carried in from another place.

water

glacier waves

wind

• Wind, water, and waves work together in the processes of deposition, weathering, and erosion

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