Download Weathering Overview

Weathering
Weathering breaks down materials
on or near Earth’s surface.
Review Vocabulary
acid: solution that contains hydrogen ions
I. Mechanical Weathering
•Mechanical weathering is a type of
weathering in which rocks and
minerals break down into
smaller pieces.
•It does not change a rock’s
composition.
A. Effect of temperature
1.Frost wedging
a. Freeze-thaw cycle of water
b. Water expands 9%
2. Breaks rock into smaller pieces
B. Effect of pressure
1. Small scale
a. Plant or tree roots wedged in
the cracks of rocks
b. Grow and expand, which
often causes the rocks to
split.
2. larger scale
a. overlying rock layers removed
by erosion or even mining
b. pressure on the bedrock is
reduced
c. bedrock surface that was
buried expands
d. long, curved cracks form
(AKA joints)
3. Exfoliation
a. outer rock layers are
stripped away
b. resulting in dome-shaped
formations
II. Chemical Weathering
A. rocks and minerals undergo
changesin their composition
1. Agents
a. water
b. oxygen
c. carbon dioxide
d. acid precipitation
2. Results
a. Dissolving Rock
b. Formation of new minerals
ex: 4Fe + 3O2
2Fe2O3
Iron Oxide (hematite)
The composition of a rock
determines the effects that
chemical weathering will have
on it.
Temperature is a significant factor in
chemical weathering because it
influences the rate at which
chemical reactions occur.
3. Composition
a. Calcite will decompose completely
in acid
ex: Limestone & Marble
4. Temperature
a. As temp. Chem. Reaction
b. Doubles every 10 oC increase
B. Effect of water
1. Universal solvent
2. Serves as a medium
3. React directly with minerals in a chemical
reaction
a. Breakdown large molecules
ex: Potassium feldspar
kaolinite
(fine-grained clay)
C. Effect of oxygen (Oxidation)
1. Iron in rocks and minerals combines
with atmospheric oxygen to form
minerals with the oxidized form
of iron. Hematite is a common
example.
Hawaii
D. Effect of carbon dioxide
1. Combines with water in atmosphere/ground
2. Forms carbonic acid
a. Acid precipitation
b. Dissolve certain rocks, such as limestone
3. Decaying organic matter adds CO2 to soil
a. Limestone caverns
E. Effect of acid precipitation
1. Burning fossil fuels
a. Sulfur dioxide
b. Carbon dioxide
c. Nitrogen oxides
2. Dissolves rocks
3. Harmful to plants and animals
III. Rate of Weathering
The natural weathering of Earth
materials occurs slowly.
However, certain conditions
and interactions can
accelerate or slow the
weathering process.
Valley of the Moon: San Juan, Argentina
A. Effects of climate on weathering
1. Chemical weathering
a. Rapid in high temperatures
b. Abundant rainfall
c. Lush vegetation
2. Physical weathering
a. Rapid in
cool
climates
Cleopatra’s Needle (NY, NY)
Pylon of Ramses (Egypt)
B. Rock type and composition
Limestone vs. granite
C. Surface area
Mechanical weathering
breaks rocks into
smaller pieces. As the
pieces get smaller,
their surface area
increases, resulting in
more total surface area
available for chemical
weathering.
D. Topography
1. Steep slopes promote erosion
2. Continually expose less-weathered
material
3. Gravity
What effects do mechanical
and chemical weathering
have on the rock at Earth’s
surface?
Answer: Mechanical weathering
breaks rock apart but does not
change its composition. Chemical
weathering dissolves some rock
and also causes some new
minerals, such as iron oxides and
clays, to form.