2. 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.
Physical/Mechanical Weathering
• when rocks are broken into smaller pieces without
changing the chemical composition of the rock
3. • Different Types of Physical
Weathering:
–Frost action/ice wedging
–Abrasion
–Exfoliation
–Wind
5. Frost action/ice wedging
• breakup of rock caused
by the freezing and
thawing (contracting
and expansion) of
water.
• Water seeps into cracks
of a rock and as the
climate cools the water
freezes and expands
breaking the rock apart.
6. Abrasion
• The physical wearing
down of rocks as they
rub or bounce against
each other.
• This process is most
common in windy
areas, under glaciers,
or in stream channels.
7. Exfoliation
• 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
9. 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.
10. Types of Chemical Weathering
• Oxidation
– when oxygen interacts chemically with minerals.
(ex. when a nail rusts)
• Hydration/Hydrolysis
– when water interacts chemically with minerals. (ex: when hornblende and
feldspar join with water they eventually form into clay)
• Carbonation
– when carbon dioxide interacts chemically with minerals. Forms carbonic
acid--> ex:dissolves
limestone creating caverns and caves.
19. Weathering Rates Depend on
3 Factors
• Particle size/surface area exposed to the surface
• Mineral composition
• Climate
20. What is the Major Product of Weathering?
• Soil:
–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.
21. Soil Horizons
• vary in depth depending on an areas climate and
weathering rates
• Soil Horizons :
– O Horizon
– A Horizon
– B Horizon
– C Horizon
– D Horizon
22. • 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 remains.
• The material helps prevent erosion, holds moisture, and
decays to form a very rich soil known as humus.
• Provides plants with nutrients
23. • 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.
• 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.
24. • 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.
25. Erosion
• Erosion refers to the transportation of rock, soil, and mineral
particles from one location to another.
• 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.
26. Factors Affecting Transportation
of Sediment
• Running water is the primary agent of erosion on Earth.
• Most running water is found in streams and rivers.
• 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.
27. Factors Affecting Transportation of Sediment
• 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 streams).
40. Deposition
• is the final step in the erosional-depositional system.
• Rock particles picked up and transported will ultimately be
deposited (left behind) somewhere else.
• 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.
42. Particle Size
• 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
bedding
• Click on picture
43. Particle Shape
• 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.
44. Density and Velocity
Density:
– If particles are the same size but have different densities the higher density
particle will settle faster.
Velocity:
– 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 well.
46. Glacial Deposition
• As glaciers move over the land they act as a
"bulldozer" changing the view of the landscape
• As glaciers pass over the land they leave
distinct features
