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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