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Two types of Weathering
• Mechanical- when rocks are broken apart
by a physical process. This does not
change the make up of the material.
• Chemical- when chemical reactions
dissolve the minerals in rocks, or changes
them into different minerals.
Mechanical Weathering
Weathering from plant roots
Burrowing animals
Exfoliation-(pressure release)
Abrasion by wind
Abrasion by water
Abrasion by Ice or Glaciers
• Glaciers carve through rock and weather it
• Evidence of glaciers- Glaciers leave
behind U shaped valleys
• Rivers leave behind V shaped valleys.
Once mechanical weathering breaks down
the rocks, more and more surface
area is exposed, and then more areas get
weathered. This speeds up the process
of the weathering.
Chemical Weathering
Once the “acid rain” falls…
• It dissolves the minerals in the rock
• This changes the rock and breaks it down
• Eventually it turns into a clay like
substance in the end called kaolinite
• This is a common in some soils (like
• The clay is an end product of weathering
Acid rain dissolved this rock
Example of the end product of Acid
What else can the acid do?
• Acid damages man-made structures as
well; limestone, marble, and sandstone
are susceptible to damage from acid
deposition, as are metals, paints, textiles
and ceramics. Repairing the damage
caused by acid rain to buildings and
monuments costs millions of dollars per
Many Caves are a result of
chemical weathering
• The carbonic acid wears away at calcite,
the main mineral in limestone
• This causes the rock to change form and
shape, and over thousands of years it
causes caves to form in spectacular ways
• The erosion or weathering causes the
minerals to breakdown into liquid form,
and then slowly solidifies causing
stalagmites and stalactites.
Stalagmites and Stalactites
Plants can also produce acid from
their roots and when they decay.
• This will dissolve minerals in rock and
weaken the rock
• Eventually the rock will break into smaller
pieces, and the process speeds up.
Another major factor in chemical
weathering is oxygen
• Oxygen aides in the process of weathering
by means of oxidation
• When metallic materials are exposed to
oxygen and water for long periods of time,
a rusting takes place, just like a chain on a
Notice the “rusty” color of the rock
and soil
Oxidized rock
Climate matters too!
• Hot and cold dry areas have less chemical
weathering, and are more prone to
mechanical weathering.
• Warm wet climate promotes chemical
weathering because of increased
exposure to the rain.
• The type of rock affects the rate that
weathering takes place.
• Some rocks weather faster than others,
and the type of climate affects different
types of rocks differently.
• When rocks weather and break down, this
is the beginning of the formation of soil.
• The two most important factors that affect
weathering are rock type and climate
What is Erosion??
• Erosion is the movement of rocks,
sediment, and/or soil.
• The main agents of erosion are wind,
water, ice, and gravity.
What is Deposition?
• Deposition is simply where sediments stop
moving, or are deposited.
• Deposition is responsible for the build up
of land formations.
• Wind erosion can happen from heavy
winds or mild winds.
• Mild winds do not have much effect on the
landscape, but heavy winds can form
Loess’ and Sand Dunes
Sand dune
LOESS (pronounced les)
Water Erosion
• Anything from a light rain, to rivers and the
oceans can cause erosion by water.
• Water’s erosive power has shaped much
of the earth’s landscape.
• Major areas of beauty such as the Grand
Canyon have been shaped by water
Erosion by Ice or Glacier
• Glaciers are large sections of ice that can
be the size of entire continents.
• Glaciers used to cover much of earth’s
surface during ice ages; now about 10
percent of earth’s land is covered by
glaciers (Antarctica and Greenland).
• Many glaciers move very slowly, and as
they do, they carry sediment with them.
Evidence of glacial erosion
Evidence of past Glaciers
• Many glaciers are valley glaciers, and are
sometimes referred to as “Ice Rivers.”
• As these glaciers move and cut their way
through the valleys, they leave a “U”
shape behind. U shaped valleys are
evidence of past glaciers.
Erosion by gravity.
• Gravity is a pulling force between two
• All objects on earth are being pulled
towards the inner core.
• Because of this force, water flows towards
the oceans, people don’t fly off of the
earth, and sediment and soils sometimes
slide downward.
Examples of erosion by gravity
• Landslides
• Mudflows
• Slumps and creeps