Forces That Shape Our Earth: Weathering And Erosion

Weathering & Erosion: Erosion and weathering are major forces that shape Earth’s surface. For example, the Grand Canyon was formed through erosion by the Colorado River running through it.

What is weathering? Weathering is the breaking down of rocks and earth materials into smaller pieces called sediment. There are two types of weathering: 1. Mechanical /Physical 2. Chemical

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

Types of Weathering: Mechanical or 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 Ways that Physical Weathering Occurs: Release of Pressure Freezing & Thawing Animal Actions Plant Growth Abrasion

Release of Pressure As the surface of a rock is eroded, the rock begins to release pressure. This 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 and over, breaking the rock apart.

Result of Freezing & Thawing

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

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. It is like using sandblasting or sandpaper on wood.

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

5 Ways that Chemical Weathering Occurs: Water Oxygen Carbon Dioxide Living Organisms Acid Rain

Water Water dissolves rocks over time. Water is the most important cause of chemical weathering

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 CO2 + rainwater = Carbonic Acid Carbonic acid weathers softer rock like limestone & marble as it seeps into spaces in rock. Examples: sinkholes and 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. Acid rain is more common around volcanic areas.