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What Causes the
Landscape to be
What is Weathering?
• Weathering is the chemical and
physical/mechanical processes that change the
characteristics of rocks on the Earth’s surface.
• Occurs when rocks are exposed to the hydrosphere
(water) and atmosphere (air)
• These weathering agents can change the physical
and chemical characteristics of rocks.
• Click for video on physical weathering
• when rocks are broken into smaller pieces
without changing the chemical composition of
• Different Types of Physical Weathering:
– Frost action/ice wedging
Frost action/ice wedging
• breakup of rock caused
by the freezing and
and expansion) of
• Water seeps into cracks
of a rock and as the
climate cools the water
freezes and expands
breaking the rock apart.
• The physical wearing
down of rocks as they
rub or bounce against
• This process is most
common in windy
areas, under glaciers,
or in stream channels.
• the peeling away of large sheets of loosened materials
at the surface of a rock.
• Common in shale, slate, and mica.
Enchanted State Rock Park, Texas
• Click for video on chemical weathering
• occurs when a rock is broken down by
chemical action resulting in a change in the
composition of a rock.
• Main agents of chemical weathering are:
• -oxygen -rainwater
• -carbon dioxide -acids produced by
decaying plants and
animals that leads to the
formation of soil.
Types of Chemical Weathering
– when oxygen interacts chemically with minerals.
(ex. when a nail rusts)
– when water interacts chemically with minerals. (ex:
when hornblende and feldspar join with water they
eventually form into clay)
– when carbon dioxide interacts chemically with
minerals. Forms carbonic acid--> ex:dissolves
limestone creating caverns and caves. Karst
Depend on 3 Factors
• Particle size/surface area exposed to the
• Mineral composition
What is a Major Product of
– is a combination of particles of rocks,
minerals, and organic matter produced
through weathering processes.
– contains the necessary nutrients to support
various forms of plant and animal life.
• As a result of weathering processes and biologic
activity, soil horizons (layers) form.
• vary in depth depending on an areas climate and
• Soil Horizons:
– O Horizon
– A Horizon
– B Horizon
– C Horizon
– D Horizon
• Horizon O refers to the organic material on the
upper most part of the profile (this layer is
usually very thin).
• Horizon A commonly known as topsoil. this
layer includes organic material (humus), such as
fallen leaves, twigs, decaying plant and animal
• The material helps prevent erosion, holds
moisture, and decays to form a very rich soil
known as humus.
• Provides plants with nutrients
• Horizon B is known as the subsoil.
• much less humus.
• usually will contain a fair amount of clay and
iron oxides, but also may contain some elements
from horizon A because of the process of
• Leaching resembles what happens in a coffee pot
as the water drips through the coffee grounds.
Leaching may also bring some minerals from
horizon B down to horizon C.
• Horizon C consists mostly of weatherized
big rocks known as Parent material (the
rock that the soil formed from).
• Horizon D which is not shown in this
illustration, usually contains solid bedrock.
• Erosion refers to the transportation of rock, soil,
and mineral particles from one location to
• Erosion is different from weathering since
erosion has the moving element.
• The main driving force behind all agents of
erosion is gravity.
• Without gravity the other major natural agents of
erosion such as: wind, running water, glaciers,
waves, and rain would not occur.
Factors Affecting Transportation
• Running water is the primary agent of
erosion on Earth.
• Most running water is found in streams and
• Sediments carried by a stream are almost always
rounded due to the grinding action of the water
on the rocks, a process called abrasion
• There are many factors that affect the movement
of sediments in a stream.
Factors Affecting Transportation
• Gradient (slope), discharge, and channel shape
influence a stream’s velocity and the erosion
and deposition of sediments
• V-shaped valleys are eroded by streams and
U-shaped valleys are eroded by glaciers
• deltas, flood plains, and meanders are results
of what a stream can form.
• The watershed of a stream is the area drained
by a stream and its tributaries (smaller feeder
• is the final step in the erosional-depositional
• Rock particles picked up and transported will
ultimately be deposited (left behind) somewhere
• Final deposition of particles (sediments) usually
occurs at the mouth of a stream. This is due to
the faster flowing stream emptying into a slower
larger body of water.
• The sediments that were once carried down the
stream are arranged from largest to smallest.
Factors Affecting Deposition
• particle size,
• density, and
• the velocity of the transporting stream.
• smaller particles settle
more slowly than the
larger particles, due to
the pull of gravity.
• The smaller particles
tend to stay in
suspension for longer
periods of time.
• This form of deposition
is called graded
• Click on picture
• A round sediment
compared to a flat
(skipping stone) sediment
of equal size will settle
faster in a body of water.
• This is due to the resistance
the flat particle will
undergo as it settles
through the water. The
round particle will meet
little resistance and settle at
a must faster rate.
Density and Velocity
– If particles are the
same size but have
the higher density
particle will settle
– velocity (speed) of the
transporting stream determines
when sediments will be deposited.
– If the stream slows down, carrying
power will decrease and the
particle sizes carried and
deposited will also decrease.
– If a stream is flowing faster, then
the carrying power of the stream
will increase and the sizes of
particles deposited will increase as