Forces That Shape Our Earth: UNIT 3: WeatheringAndErosion

Weathering & Erosion:  For example, the Grand Canyon was formed through erosion by the 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? Weathering: The breaking down of rocks into smaller pieces. 1. Mechanical /Physical 2. Chemical Hulk Rock Smash!

Types of Weathering: Mechanical/Physical: Rock is physically broken into smaller pieces (larger pieces become smaller pieces of the same rock) Chemical: Rock is chemically changed (like rusting or dissolving away)

5 Agents of Mechanical Weathering: 1. Release of Pressure 2. Freezing & Thawing 3. Animal Actions 4. Plant Growth 5. Abrasion

Release of Pressure  As the surface of a rock is eroded, the rock begins to release pressure  Causes top layers of the rock to crack and flake off

Release of pressure: rock cracks like an egg shell

Freezing & Thawing When water in the cracks of rocks freezes it expands causing the crack to enlarge or get bigger. The ice melts & refreezes over & over, breaking the rock apart.

Result of Freezing & Thawing

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

Plant Root Growth Plants roots can grow into cracks in the rock, slowly breaking them apart.

Abrasion Sand and other rock particles in wind, water or ice can wear away exposed rock surfaces. Sand and other rock particles in wind, water or ice can wear away exposed rock surfaces. Like sandblasting or sandpaper on wood Like sandblasting or sandpaper on wood

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

5 Agents of Chemical Weathering 1. Water 2. Oxygen 3. Carbon Dioxide 4. Living Organisms 5. Acid Rain

Water  Water dissolves rock  Water is the most important cause of chemical weathering  Moving water is THE STRONGST weathering force that changes the land we see

Oxygen  Oxygen + Water + Iron = Rust through the Chemical reaction called Oxidation  Rock will become crumbly, soft, and appear reddish-brown in color

Rusted rock on hillside

Carbon Dioxide CO 2 + rainwater = Carbonic Acid Carbonic Acid weathers softer rock like limestone & marble as it seeps into spaces in rock. Ex: sinkholes, caves

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

Lichens grow on rock

Acid Rain  Acid rain causes rocks to weather very rapidly.

So what is erosion? Erosion: The movement of weathered rock by wind, water, glaciers & gravity