Transcript Chapter 3

Chapter 14
Weathering and Erosion
Weathering Processes
Weathering - the natural process by which
atmospheric and environmental agents, such
as wind, rain, and temperature changes,
disintegrate and decompose rock at or near
the surface.
There are two main types of weathering
processes—mechanical weathering and
chemical weathering.
Each type of weathering has different effects
on rock.
Mechanical Weathering
Mechanical weathering is strictly a physical
process and does not change the
composition of the rock.
Common agents of mechanical weathering
are ice, plants and animals, gravity, running
water, and wind.
Physical changes within the rock itself
affect mechanical weathering.
Ice Wedging
Thermal expansion
Repeated daily heating and cooling of
rock;
Heat causes expansion; cooling causes
contraction.
Expanding and contracting causes
cracks.
Abrasion
Is the grinding and wearing away of rock
surfaces through the mechanical action of
other rock or sand particles
Abrasion is caused by gravity, running
water, and wind.
Organic
Wedging
Plants and
animals
Root wedging
widens fractures
in rock.
Organic Activity
Digging and burrowing activities.
Earthworms and other animals that move
soil expose new rock surfaces to both
mechanical and chemical weathering.
Chemical Weathering
Chemical alteration of minerals.
Chemical reactions commonly occur
between rock, water, carbon dioxide,
oxygen, and acids.
Most effective in a warm, humid climate.
Chemical weathering changes both the
composition and physical appearance of the
rock.
OXIDATION
ROCKS / MINERALS
CHEMICALLY REACT
WITH THE OXYGEN IN
THE ATMOSPHERE,
CAUSING A
DECOMPOSITION ON
THE MATERIALS
Dissolution - mineral completely
dissolves, leaving only ions in solution.
Section 2 Rates of Weathering
Factors influencing Weathering Rates
The processes of mechanical and
chemical weathering generally work
very slowly.
Rock Structures – chemical/mineral
composition, Physical features
Topography
Climate
Spheroidal Weathering
Spheroidal
Weathering
Differential Weathering
Rocks weather at different rates.
Softer rocks are less resistant to weathering.
Section 3 Soil
Characteristics of Soil
The characteristics of soil depend mainly on
the rock from which the soil was weathered,
which is called the soil’s parent rock.
Soil Composition
Soil composition refers to the materials of
which it is made.
The color of soil is related to the
composition of the soil.
Soil moisture can also affect color.
Soil Horizons
Horizon O
Bedrock
O-HORIZON
A-HORIZON
B-HORIZON
Section 4 Erosion
erosion a process in which the materials of Earth’s
surface are loosened, dissolved, or worn away and
transported from one place to another by a natural
agent, such as wind, water, ice, or gravity
When rock weathers, the resulting rock particles
do not always stay near the parent rock.
Various forces may move weathered fragments of
rock away from where the weathering occurred.
Soil Erosion
Ordinarily, new soil forms about as fast as
existing soil erodes.
Some farming and ranching practices
increase soil erosion.
Soil erosion is considered by some
scientists to be the greatest environmental
problem that faces the world today.
Soil Conservation
Certain farming techniques can increase the
rate of erosion.
Land clearing accelerates topsoil erosions.
Soil erosion can be prevented by soil
conservation methods
Soil Conservation Methods
Contour Plowing
Strip-Cropping
Terracing
Crop Rotation
End of Chapter 14