Recall
Notes
42 – Weathering- breakdown of rock due to exposure to the
atmosphere.
43- Weathering involves 2 processes.
43- Chemical
43- Mechanical (Physical)
43- Chemical- (decomposition)- Some of the rock’s minerals
are turned into a different substance.
5 causes of chemical Weathering:
-water
-air
-Acids in precipitation (acid rain)
-Acids in ground water (mines)
-acids in living things (lichens)
3 Types of chemical weathering:
Dissolution- Compounds are dissolved (Limestone to
caves)
Oxidation- Mineral ions combine with oxygen which
creates rust
Hydrolysis- acid rain reacts with rock-forming minerals
such as feldspar to produce clay and salts that are
removed in solution.
43 –Mechanical Weathering – Disintegration: Physically
breaking down the rocks without changing the chemical makeup.
4 main sources of mechanical weathering
- Gravity
- Water
- Wind
- Waves
43 KEY POINT: If a particle is loosened by weathering and
stays put, it is weathering. If it begins to move it is erosion.
Mechanical weathering can be erosional.
Types of mechanical weathering:
-frost wedging- freezing and thawing of water causes
rocks to crack.
-exfoliation- peeling off of sheets of rock layers
-crystal growth wedging- involves salt crystals growing
from salty waters
-Root penetration- Strong plant roots grow into the rocks
which causes fractures
-Abrasion- Wind and water can cause rock fragments to
bounce off of each other breaking down the rocks.
-Glacier Weathering- Ice and rock interact
-Other agents of weathering: flash floods, mud slides,
and land slides