Weathering
& Soil
Weathering
Weathering & its effects
• Surface processes that break down
rock.
• Sediments: sand, silt, & clay
• Weathering changes the Earth’s
surface.
dark
Mechanical Weathering
• Occurs when rocks are broken apart
by physical processes.
Caused by:
• Growing plants
• Burrowing animals
• Expanding ice
• Ice wedging occurs where water enters
cracks in rocks, freezes, & expands.
• As surface area increases, more rock is
exposed to be weathered.
Chemical Weathering
• Chemicals dissolve the minerals in rocks
or change them into different minerals.
• Naturally formed acids can weather rocks
chemically
•Carbonic acid forms when Carbon dioxide
mixes with water. The acid reacts with calcite
in limestone to form caves.
• Some roots &
decaying plants give
off acids that
dissolve minerals in
rock.
• Oxidation occurs
when some materials
are exposed to
oxygen and water.
(Rust)
Effects of Climate
• Mechanical weathering occurs more in
cold climates.
• Chemical weathering occurs more in
warm, wet climates.
• Rock type can affect the rate of weathering
in a particular climate.
Soil
A. Formation of Soil
•Weathering gradually breaks rocks into
smaller and smaller fragments.
•Plants and animals add organic matter to
the rock fragments.
• Soil is a mixture of
Weathered rock
Decayed organic matter
Mineral fragments
Water
Air
• Causes for soil formation include:
Climate
Slope
Types of rock
Types of vegetation
Length of time that rock has been
weathering
Composition of Soil
•Decayed organic matter turns into a darkcolored material called humus.
•Humus provides nutrients for plants.
•Burrowing creatures mix humus with the
other rock fragments.
Soil Profile
A Horizon (topsoil)
•Can be covered by litter, organic
material that will eventually become
humus and helps prevent erosion.
B Horizon
•Lighter in color & contains less humus.
•Leeching is the removal of minerals that
have been dissolved by water.
•Water reacts with humus & carbon
dioxide to form acid.
C Horizon
• Made of partially weathered rock and is
found at the bottom of a soil profile.
Soil Types
•Different types of soil vary in color, depth,
texture, & fertility.
•The type of soil depends on the region’s
climate.
•Deserts are dry, prairies are semi-dry, &
temperate forests are mild & moist.
Soil Erosion
Soil – An Important Resource
•Soil is eroded when it is moved to a
new location by wind or water.
•Soil erosion removes topsoil that is
important for plant growth.
Causes and Effects of Soil Erosion
•Human activities can increase the rate of
soil erosion.
•Soil erosion occurs rapidly on steep
slopes and areas that are not covered by
vegetation.
•Forest harvesting & overgrazing
contribute to the rate at which erosion
can occur.
Preventing Soil Erosion
• Farmers reduce erosion by planting
shelter belts, using no-till farming, and
planting cover crops after harvesting.
• Contour farming and terracing are used to
control erosion on slopes.
•Rows of trees (windbreaks) are planted on
the plains to reduce erosion caused by wind.