Weathering and Erosion

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Weathering and Erosion
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Weathering, Erosion, Deposition, and Landscapes
Weathering the mechanical and chemical
processes that change objects on Earths surface
over time.
Erosion the removal of weathered material from
one location to another the sediments are
transported by wind, gravity, glaciers, man, and
running water.
Deposition the process whereby these sediments
are released by their transporting agents
(dropped).
Weathering breaks down the rocks, erosion moves
the particles, and deposition drops the sediments
in another location.
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Weathering responsible for limited changes in
Earths surface dissolving, crumbling or
weakening a rock. Can take thousands of
years. Two forms physical and chemical
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Erosion responsible for large scale changes in
the form of the Earth. Rivers, valleys, and
canyons are created by the erosion of weakened or
disintegrated rock. Can take thousands of years
or minutes.
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Water is a major factor in weathering. Rain
splashes mud Puddles form
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• Water flows along surface, moving downhill.
• Little water paths become rills.
• Rills deepen into creeks, then streams, and
  finally, rivers.
• Water digs deeper channels and carries more earth
  and rock from shores and bottom.

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Stream
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Large river
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There are two primary types of weathering Chemica
l and Physical
1. Physical Weathering the breakdown of rocks
and minerals into smaller pieces without a change
in chemical composition.
Causes of physical weathering 1.
Freeze/thaw 2. Wedging by plant roots 3.
Day/Night temperature fluctuations 4. Loss of
thin surface of rocks by exfoliation or
abrasion 5. Gravity causing rocks to fall from
heights and then breaking into pieces 6.
Animals, including people, digging into rocks
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Freezing Thawing

• When water in the cracks of rocks freezes it
  expands causing the crack to enlarge or get
  bigger. The ice melts refreezes over over,
  breaking the rock apart.

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Result of Freezing Thawing
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Wedging by plant roots
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Day/Night Temperature fluctuations
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Exfoliation
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Abrasion, wind erosion
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Gravity
After May 5, 2003
Old Man in the Mountain, NH before May 5, 2003
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Animal actions
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• Physical weathering exposes new surfaces and
  pieces.
• New surfaces can be physically or chemically
  weathered

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• Chemical Weathering Decomposition of rock
  material due to the chemical reaction of
  compounds in the rock with chemicals in the
  environment.
• Not all rocks are composed of the same chemicals
  or minerals, so chemical weathering affects
  different rocks differently.

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Chemical weathering occurs at the surfaces of
rocks. When physical weathering results in
freshly exposed rock surfaces, agents of chemical
weathering have new material to decompose.
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Chemical Weathering occurs when elements and
minerals in rocks react with chemicals from the
environment. The rock breaks down at the same
time as it changes chemical composition. The end
result is different from the original rock.
There are 3 main types of chemical weathering
1. Oxidation oxygen combines with the elements
in the rock and it reacts. This the scientific
name for rust.
2. Hydration water reacts with the minerals in
rocks and can dissolve certain minerals.
3. Carbonation carbon dioxide dissolves in
water to form carbonic acid. This makes acid
rain which chemically weathers (dissolves) rocks.
Other acids, like sulfuric acid, also combine
with water to make acid rain.
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Chemical Weathering H2O CO2
? H2CO3 water carbon dioxide ?
carbonic acid
Statue created in 1702, Germany Picture on left,
taken 1908 (after 206 years) Picture on right,
taken 1969 (61 years later)
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There are 4 factors that effect the rate of
weathering
1. Surface Area (exposure) - Exposing more
surface area will increase the rate of
weathering.
2. Particle Size Larger particles weather
slower and smaller particles weather at a faster
rate.
3. Chemical Composition (what a rock is made of)
Certain rocks and minerals are naturally weaker
than others, while others are more resistant
(stronger).
4. Climate Warmer, moister climates have the
most weathering. Heat water speed up all
chemical reactions. This is the most important
factor in weathering.
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Erosion (transport)

• There are 5 main agents of erosion
• Running Water
• Glaciers
• Wind
• Gravity
• Man

Weathering has to happen before erosion. The
rocks have to be broken into smaller sediments
before they can be eroded away.
Wind Erosion
Glacier
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There is a pile of weathered material at the
bottom. It is slowly being eroded down hill by
gravity.
Mount Rushmore
It will not be there forever!!
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• Water, wind, or gravity exert a force on the soil
  material, causing it to move.
• When erosion occurs on a slope, soil is washed
  from the slope. The steeper the slope, the more
  erosion can occur.
• Obstacles like rocks and vegetation can slow the
  progress of erosion or divert the path of the
  erosion.
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Investigation 1

• CaCO3 2HCl ? CaCl2 CO2 H2O
• Calcium Hydrochloric
  Calcium Carbon Water
• carbonate acid
  chloride dioxide
• GAS
• Marble consists
  mostly of the mineral calcium
  carbonate (CaCO3)

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Mantle Convection and Plate Tectonics
Hot mantle rises, cools at surface and
sinks. Crust floats on mantle. New crust
material comes from rising mantle, pushes old
crust away.
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Mantle Convection and Plate Tectonics
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Plate Tectonics Over Geologic Time
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Wind erosion
Sand grains carried by strong and consistent
winds act as abrasives capable of sculpting solid
rock.
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Wind erosion

• Soil erosion in cultivated farmlands can result
  in devastating dust storms.

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Water erosion
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Water erosion
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Factors that influence water erosion

• Rainfall intensity and runoff heavy bursts of
  hard rain cause more soil erosion than light
  rain. Heavy rains can saturate soil and create
  puddles that flow with gravity and start erosion

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Factors that influence water erosion

• Slope gradient water erosion is more likely on
  steeper surfaces, water moves very quickly down
  the side of a steep hill
• Vegetation plant roots can absorb water, hold
  soil, leaves and branches absorb energy of
  raindrops

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Rock Cycle

• http//www.classzone.com/books/earth_science/terc/
  content/investigations/es0602/es0602page02.cfm
  Interactive rock cycle

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Soil forms from the weathering of the rock below
it. The solid rock below is called Bedrock. The
rock is exposed to wind, rain etc The rock
breaks down over time to form soil. Soil has
different layers called Soil Horizons.
O- Horizon the very thin surface covering (not
really a layer) A Horizon (TOPSOIL) dark
surface soil that contains a lot of living
material and dead plant/animal remains (humus).
This is the layer with all of the nutrients
needed to grow plants. B-Horizon (SUBSOIL)
lighter colored soil with less nutrients and more
clay C-Horizon (REGOLITH) larger rock fragments
that sit on top of the unweathered bedrock
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Soil

• Soil is the product of weathering and erosion.

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What do you see in the soil?