Weathering The natural breaking down of rocks and

other materials on the Earth’s surface. A slow continuous process that affects all

substances exposed to the atmosphere. Two types of weathering:

Mechanical Chemical

Weathering

Mechanical Weathering Forces of nature break rock into

smaller pieces without changing the chemical make up of the rock.

Rocks are broken into smaller pieces Fragments tend to become rounder

as weathering continues. 5 types of Mechanical Weathering

Mechanical Weathering Video Clip

Temperature Repeated heating

and cooling of outer surface of rock causes outer layers to break off.

Breaking of outer layers called: Exfoliation.

Ice Wedging Water seeps into

cracks in rocks. Temperature drops

and water in cracks freezes and expands widening the crack.

Organic Activity Mechanical

Weathering caused by plants or animals. Could be animals

simply walking. Root-pry: roots in

cracks of rocks widen cracks as the root grows.

Examples of Weathering

Gravity Pulls loose material down. As rocks fall they collide and break.

Abrasion Wearing away by solid particles

carried by wind or water.

Chemical Weathering Weathering which changes the

mineral composition of rocks through chemical reactions.

Most often involves water.

3 Types of Chemical Weathering

1. Water• Water dissolves minerals and carries them away.• Water can form weak acid with many chemicals.

2. Acid formation• Mild acids form and breakdown minerals• Plants (Lichens) can often form mild acids that

breakdown rock material

3. Oxidation• Oxygen in the air combines with minerals to form new

compounds• Rusting is an example

Chemical Weathering

Factors That Influence the Rate of Weathering Type of rock

Rock that is more resistant to chemical weathering are called a Stable Rock.

Amount of moisture present: Climate The more moisture, the faster weathering

occurs. The amount of living organisms.

The amount of exposed surface a rock has.

Time