Weathering
• weathering
• mechanical weathering
• chemical weathering
• oxidation
Weathering and Its Effects
The mechanical and chemical processes that change
objects on Earth’s surface over time are called
weathering.
Over thousands of years, weathering can break rock into
smaller and smaller pieces, such as sand, silt, and
clay.
Mechanical Weathering
When physical processes naturally break rocks into
smaller pieces, mechanical weathering occurs.
The chemical makeup of a rock stays the same during
mechanical weathering.
Mechanical weathering can be caused by ice wedging,
abrasion, plants, and animals.
Mechanical Weathering (cont.)
An example of mechanical weathering is when the
intense heat of a forest fire causes nearby rocks to
expand and crack.
When something is broken into smaller pieces, it has a
greater surface area.
Surface area is the amount of space on the outside of an
object.
Chemical Weathering
Dr. Marli Miller/Getty Images
Chemical weathering
changes the materials
that are part of a rock into
new materials.
These granite obelisks show
how chemical weathering
can affect some rock.
Chemical Weathering (cont.)
Water is important in chemical weathering because most
substances dissolve in water.
The process of dissolving breaks up the minerals in the rock
into small pieces. The small pieces mix with water to form
a solution and are washed away from the rock.
Acids are also agents of chemical weathering and cause
more chemical weathering than pure water does.
Chemical Weathering (cont.)
Oxidation combines the element oxygen with other
elements or molecules.
The product of oxidation is called an oxide.
When rocks that contain iron oxidize, a layer of iron oxide
forms on the outside surface.
What affects weathering rates?
The environment helps determine the rate of weathering.
Mechanical weathering occurs fastest in locations that have a
lot of temperature changes.
Chemical weathering is fastest in warm, wet places.
The type of rock being weathered also affects the rate of
weathering and determines what kinds of products result.
The Erosion-Deposition Process
• erosion
• deposition
Reshaping Earth’s Surface
A combination of constructive processes and destructive
processes produce landforms.
Constructive processes build up features on Earth’s surface.
Destructive processes tear down features on Earth’s surface.
The breakdown of rock—weathering—
is one type of destructive process that changes Earth’s surface.
A Continual Process of Change
Chemical weathering alters the chemical composition of
rock.
Physical weathering is the breaking of rock into pieces,
called sediment, without changing the chemical
composition of the rock.
Water, wind, and ice are agents, or causes, of weathering.
Erosion
Erosion is the removal of weathered material from one
location to another.
Agents of erosion include water, wind, glaciers, and gravity.
Factors that affect the rate of erosion include weather,
climate, shape of the land, and type of rock.
Erosion (cont.)
The presence of plants and the way humans use the land
affect the rate
of erosion.
The rate of erosion sometimes
depends on the type of rock.
Weathering breaks some types of rock into large pieces.
Other rock types easily break into smaller pieces that are
more easily transported.
Deposition (cont.)
Deposition is the laying down or settling of eroded
material.
As water or wind slows down, it has less energy and can
hold less sediment, which can result in some of the
sediment being deposited.
Sediment is deposited in locations called depositional
environments, such as swamps, deltas, beaches, and the
ocean floor.
Interpreting Landforms (cont.)
Landforms created by deposition are often flat and lowlying.
An apron of sediment, called an alluvial fan, often forms
where a stream flows from a steep, narrow canyon onto a
flat plain at the foot of a mountain.