Forces That Shape Our Forces That Shape Our Earth:Earth:

UNIT 3:UNIT 3:WeatheringWeathering

AndAndErosionErosion

Weathering & Erosion:Weathering & Erosion:

For example, the Grand Canyon For example, the Grand Canyon was formed through erosion by the was formed through erosion by the Colorado River running through it!Colorado River running through it!

Why is this important? Erosion and weathering are major forces that shape the world around us. Understanding these forces helps us to understand the way our land is shaped – from rivers to canyons.

People play a part in the way and amount that our soil erodes around us. It is important for us to understand how erosion works and the effects on soil.. Especially since we depend on soil for our food production! If we don’t take care of the soil, we will starve.

What is weathering?What is weathering?

WeatheringWeathering:: The breaking down The breaking down of rocks into smaller pieces.of rocks into smaller pieces.

1. Mechanical /Physical1. Mechanical /Physical

2. Chemical2. ChemicalHulk Rock

Smash!

Hulk Rock

Smash!

Types of Weathering:Types of Weathering:

Mechanical/Physical:Mechanical/Physical:

Rock is physically broken into smaller Rock is physically broken into smaller pieces (larger pieces become smaller pieces (larger pieces become smaller pieces of the same rock)pieces of the same rock)

Chemical:Chemical:

Rock is chemically changed (like Rock is chemically changed (like rusting or dissolving away)rusting or dissolving away)

5 Agents of 5 Agents of Mechanical Mechanical WeatheringWeathering::

1.1. Release of PressureRelease of Pressure

2.2. Freezing & ThawingFreezing & Thawing

3.3. Animal ActionsAnimal Actions

4.4. Plant GrowthPlant Growth

5.5. AbrasionAbrasion

Release of PressureRelease of Pressure

As the surface of a rock is As the surface of a rock is eroded, the rock begins to release eroded, the rock begins to release pressurepressure

Causes top layers of the rock to Causes top layers of the rock to crack and flake offcrack and flake off

Release of pressure: rock Release of pressure: rock cracks like an egg shellcracks like an egg shell

Freezing & ThawingFreezing & ThawingWhen When waterwater in the cracks in the cracks

of rocks of rocks freezesfreezes it it expands expands causing the causing the crack tocrack to enlarge or enlarge or get get biggerbigger. The ice melts & . The ice melts & refreezes over & over, refreezes over & over, breaking the rock apart.breaking the rock apart.

Result of Freezing & ThawingResult of Freezing & Thawing

Animal ActionsAnimal Actions

Animals digAnimals dig (burrow) through (burrow) through the ground to make their the ground to make their homes. homes. This loosens the soil & This loosens the soil & breaks apart rocksbreaks apart rocks..

Plant Root GrowthPlant Root Growth

Plants Plants rootsroots can can grow into grow into cracks in the rock,cracks in the rock, slowly slowly breaking them apart.breaking them apart.

AbrasionAbrasion SandSand and other rock particles and other rock particles in in

wind, water or ice can wear wind, water or ice can wear awayaway exposed exposed rockrock surfaces. surfaces.

Like sandblasting or sandpaper Like sandblasting or sandpaper on woodon wood

Chemical WeatheringChemical Weathering

The process that breaks down The process that breaks down the surface of rock by the surface of rock by chemical changes.chemical changes.

5 Agents of 5 Agents of Chemical Chemical WeatheringWeathering

1.1. WaterWater

2.2. OxygenOxygen

3.3. Carbon DioxideCarbon Dioxide

4.4. Living OrganismsLiving Organisms

5.5. Acid RainAcid Rain

WaterWater Water Water dissolves rockdissolves rock

Water is the Water is the most important causemost important cause of of chemical weatheringchemical weathering

Moving water is THE STRONGST Moving water is THE STRONGST weathering force that changes the land weathering force that changes the land we seewe see

OxygenOxygenOxygen + Water + Iron = RustOxygen + Water + Iron = Rust

through the Chemical reaction through the Chemical reaction called called OxidationOxidation

Rock will become crumbly, soft, Rock will become crumbly, soft, and appear reddish-brown in colorand appear reddish-brown in color

Rusted rock on hillsideRusted rock on hillside

Carbon DioxideCarbon Dioxide

COCO22 + rainwater = Carbonic Acid + rainwater = Carbonic Acid

Carbonic Acid weathers softer rockCarbonic Acid weathers softer rock like limestone & marble as it seeps like limestone & marble as it seeps into spaces in rock.into spaces in rock.

Ex: sinkholes, cavesEx: sinkholes, caves

Living OrganismsLiving Organisms

The The roots of plants make a roots of plants make a weak acidweak acid that slowly that slowly dissolves rocks around the dissolves rocks around the plant.plant.

Lichens grow on rockLichens grow on rock

Acid RainAcid Rain

Acid rain Acid rain causes rocks to causes rocks to weather very rapidlyweather very rapidly..

So what is erosion?So what is erosion?

Erosion:Erosion:

The movementThe movement

of weathered of weathered

rock by wind, rock by wind, water, glaciers water, glaciers & gravity& gravity