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Weathering and Erosion
What is Weathering?
• Weathering is
the chemical
and physical
processes that
break down rock
on Earth’s
surface.
What does weathering do?
• The forces of
weathering
breaks rocks
into smaller
and smaller
pieces
All of these contribute to
weathering
•
•
•
•
•
Heat
Cold
Water
Ice
Oxygen and
carbon dioxide
in the
atmosphere
Mechanical Weathering
• Mechanical weathering breaks
rock into pieces by freezing and
thawing, release of pressure,
growth of plants, actions of
animals, and abrasion.
Ice Wedging
• When ice melts,
the water seeps
deep into the
rocks and
refreezes.
• The rock expands
and contracts,
breaking the rock
down.
Release of pressure
• When a large piece of rock
reaches the surface, the
pressure on it is reduced. This
causes the rock to flake off.
Growth of plants
• Plant roots can grow in cracks in
rocks, as the roots grow it
cracks the rocks more.
Actions of animals
• Animals can dig, burrow, or
break down rocks.
Abrasion
• The grinding
away of rock by
rock particles
carried by
water, ice, wind,
or gravity.
Chemical Weathering
•
•
•
•
•
•
The agents are:
Water
Oxygen
Carbon dioxide
Living things
Acid rain
Water
• Water is the
most important
agent of
chemical
weathering.
• Over time rocks
will dissolve in
water.
How Does Oxygen Change
Rocks?
• Oxygen mixes with rocks and
rusts.
• It makes them soft and
crumbly.
• It makes the rock appear red.
Carbon Dioxide
• This type of chemical
weathering causes acid rain.
Living Things
• Plants can grow
in cracks.
• The plant’s
roots can
dissolve rocks.
Acid Rain
• For over 150 years, people have
been burning coal, oil, and gas.
• Burning these fossil fuels can
pollute the air with acid.
• These acids mix with rain and
fall as acid rain.
Rate of Weathering
• Two things
affect rate:
-Type of rock
-Climate
Types of Rock
• Rocks with lots
of pores
weather
easiest.
• These rocks are
said to be
permeable.
Climate
• Climate is the
average weather
conditions in an
area.
• Chemical
reactions occur
faster in areas
that are hot and
wet.
What is Erosion?
• Erosion is the
movement of
rock particles
by wind, water,
ice or gravity.
Wind Erosion
• Fast moving wind can carry sand
and dust that scour and
weather the surfaces they
strike.
Water Erosion
• Sediments being moved by
running water. (river, stream,
flash flood, etc.)
Ice Erosion
• Glaciers move over land moving
a depositing sediments.
Gravity Erosion
• This is the underlying force of
erosion and deposition. Cause
glaciers to move, and sediments
to leave wind or water, or
causes landslides and mudflows.
What is Deposition?
• When moving water, ice, wind,
or gravity drops a load of Earth
materials in a new place.
Review
• 1. What factors cause
mechanical weathering?
• 2. Name 3 things that cause
chemical weathering.
• 3. What factors affect the rate
of weathering.