Surface Processes:
Weathering, Erosion, and
Deposition
Now that you know how rocks are formed,
you will find out how they are broken down.
I. Weathering- the physical and chemical
breakdown of rocks at or
near the surface.
A. Types of Weathering
1. Physical Weathering-the mechanical
or physical breakdown of rock into
smaller pieces(sediments), without a
change in the mineral’s chemical
composition.
a. Frost Action-water freezes in a crack of
the rock surface, expanding
and splitting the rock.
Alternate freezing and thawing
form potholes and frost heave.
b. Plants and Animals-plant roots force their
way into cracks, animals uncover rock
and expose it to the elements.
c. Exfoliation Dome-layers of rock peel off
the main body of the rock.
Casper, Wyoming
d. Temperature Changes-alternating hot
and cold temperatures weaken the
rock as it expands and contracts.
e. Abrasion-pieces of rock collide with
each other due to transportation
by wind, ice, water and gravity.
water
wind
2. Chemical Weathering-the process by
which chemicals breakdown rock
through a change in the mineral’s
composition, happens fastest in
a hot, moist climate.
a. Oxidation-occurs when oxygen
from the air combines with
iron-rich minerals of the rock,
oxidation = RUST.
b. Carbonation-occurs when water
combines with carbon dioxide
in the air to form carbonic acid.
Carbonic acid easily dissolves
rocks like limestone and marble.
c. Hydrolysis-water combines with
minerals such as mica and
feldspar found in granite, to
form clay, the rock weakens and
crumbles apart.
B. Factors Affecting the Rate of Weathering
1. Exposure-rate and type of weathering
are dependent on exposure to air,
water and living things.
The greater the amount of rock
exposed, the greater the
weathering.
This is a direct relationship.
2. Particle Size-an increase in surface area
increases the rate of weathering.
Example: Granulated sugar dissolves faster
than a cube of sugar. More surfaces
are exposed when cut.
Rate of
Weathering
Fast
Slow
Surface Area
3. Mineral Composition-rocks made of harder
minerals weather slower than rocks
made of softer minerals.
Rate of
Weathering
Fast
Slow
Mineral Hardness
Which rock is most resistant to weathering?
3
4. Climate-physical and chemical weathering
are affected by climate.
a. In cold and moist climates, physical
weathering is dominant.
b. In hot and moist
climates, chemical
weathering is
dominant.
Cleopatra’s Needle
c. In both cases, water is the major
ingredient that promotes weathering.
5. Time-as time goes on, more weathering
occurs.
6. Humans-excavation of land, mining,
building, etc.
C. Soil Formation-end product of weathering
and biologic activity.
Time increases
1. Factor’s Affecting Soil Formation
a. Parent Material(bedrock)
• Residual soil—soil is formed from the
parent material and is of
the same composition.
• Transported
soil—parent material has
been carried from
elsewhere and
deposited
Most NYS soil was transported from glaciers.
b. Climate
• Arid climates have thin soils, high in
mineral content, low in organic
matter.
•Humid climates have thick soils, high
in organic matter, low in mineral
content.
c. Organisms
• Dead and decayed plants and animals
add nutrients, forming topsoil.
d. Time-the longer the weathering,
the deeper the soil.