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Weathering

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Title: Weathering & Erosion Author: Laptop Last modified by: jwilliams Created Date: 12/2/2002 2:54:07 PM Document presentation format: On-screen Show (4:3) – PowerPoint PPT presentation

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Title: Weathering


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Weathering
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  • Weathering is the physical and chemical breaking
    down of rock material into smaller fragments due
    to exposure to processes that occur at Earths
    surface
  • Weathering occurs when rocks in the lithosphere
    are UPLIFTED and is exposed to the atmosphere,
    hydrosphere, and biosphere

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Weathering
  • The most important agent involved in the
    weathering of material is WATER

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Two Types OF Weathering
  • 1) Physical weathering is breaking rock by force
    into smaller pieces of the SAME material
  • ex hitting, scratching, cracking
  • 2) Chemical weathering is the chemical reaction
    of water and water vapor breaking down rock by
    changing its chemical composition
  • The minerals that make up the rocks are changed
    into another substance

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4 Types of Physical Weathering
  • 1) Frost action
  • (ice wedging)- water seeps into cracks, freezes,
    expands and wedges the rock apart!
  • Water and ice are more powerful than rock over
    time!
  • Water seeps into small cracks in rocks.
  • When the water freezes it expands creating great
    pressure.
  • The crack widens and allows water to seep deeper
    into the rock.
  • Alternating Freezing and Thawing

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Examples of Frost Wedging Potholes
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  • 2) Plant action
  • tree roots grow into small fissures or wedges
    and expand rock
  • Tiny root hairs seek out small cracks and pits in
    rock.
  • Once the root hairs find a place they grow and
    expand.
  • The expansion causes great pressure and cracks
    the rock.

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  • 3) Exfoliation
  • the peeling of rock due to release of pressure
    experienced when rock was formed
  • Rocks formed deep in the Earth are made under
    high pressure.
  • When the pressure is released the rocks expand
    crack.
  • May also be caused by alternate heating and
    cooling of rocks by weather conditions.
  • This is basically the peeling away of rock

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Water (especially in streams
  • 4) Abrasion-
  • collision of rocks with one another
  • Scraping, grinding, and wearing away other rocks
    during erosion (movement)

WIND
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Types of Chemical Weathering
  • Oxidation
  • Hydrolysis (water)
  • Carbonation (acid rain)

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  • Oxidation
  • rocks with metallic elements combine with oxygen
    (in air and water) and rust away (rust stains the
    rocks REDDISH BROWN)
  • ex. rusting

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  • Water (hydrolysis)
  • Minerals are dissolved in water when they react
    with it
  • ex. Feldspar reacts with water to form kaolinite
  • Much of the time these minerals will end up as
    clay

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  • Acid-Carbonation
  • carbon dioxide from air reacts with water to
    create carbonic acid which breaks down rocks
    (especially limestone, marble, etc.)
  • Why? What mineral does these rocks have in them?

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  • Acid Rain Sulfur Dioxide in the atmosphere
    dissolves in rain water forming a strong acid
    (sulfuric acid).

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NOTE chemical weathering typically results in a
rounded appearance of the landscapejust like
here in the Catskills!
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Carbonation Stalagtites and Stalagmites (karst
topography)
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Carbonation Karst Topography
  • Karst Topography is the name given to a region
    where the bedrock is easily chemically weathered
  • This leads to the rock weathering away and
    forming sinkholes, caverns, disappearing streams

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Karst Topography
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Differential Weathering
  • Masses of rock do not weather uniformly due to
    regional and local factors
  • Results in many unusual rock formations
  • Example Bryce Canyon

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Bryce Canyon National Park
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Rates of weathering (how fast rocks break down
due to physical or chemical processes) will be
influenced by
  • 1) Surface area exposed - weathering occurs on
    the surface. The more surface exposed, the faster
    the weathering will occur.

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A smashed piece has greatest surface area
exposed. The interior can now be attacked.
A full, solid block has the least surface area.
The interior is safe from exposure.
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Rates of Weathering will depend on
  • 2) Rock and Mineral composition- some minerals
    are more resistant than others.
  • Sedimentary rocks are generally soft and weather
    fast.
  • Limestone is easily dissolved by acids.
  • Igneous and metamorphic rocks are usually dense,
    hard, and more resistant to weathering.
  • Any rock containing quartz (hardness of 7) will
    generally be resistant to weathering
    (conglomerate, quartzite, granite, etc.)

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Rate of Weathering will depend on
  • Exposure to surface rocks exposed at surface
    weather much more quickly than buried rock.
  • Rock Outcrops are places where rock layers
    actually stick out above groundwhere they are
    quickly exposed to lichens, moss, trees,
    rainfall, ice, and animals!

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Rate of weathering will depend on
  • Topography higher elevations tend to be colder
    and experience more freeze-thaw cycles

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Where is the rock more resistant to weathering?
F
A
C
E
B
D
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Where is the rock least resistant to weathering?
F
A
C
E
B
D
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You might also see it like this
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You might also see it like this
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Rates of Weathering will depend on
  • Climatic Conditions
  • Cold and/or dry climates favor physical
    weathering.
  • Warm and wet climates favor chemical weathering.
  • Frost action works best in areas where the
    temperature fluctuates wildly.

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Soil - The product of weathering
  • Soil-Soil is the result of weathering of rock,
    which produces smaller pieces called fragments,
    which combine with organic matter, air, and water
    to comprise soil. Soil rock fragments, humus
    (decayed plant and animal material), air and
    water
  • Soil forms layers of different characteristics
    called horizons.

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Soil Horizons
  • Soil separates over time into distinct layers as
    follows
  • A horizon (Topsoil) the upper layer of dark
    brown soil containing humus and plenty of animal
    activity (bugs, worms, etc.)
  • B horizon also called subsoil, containing many
    more minerals leached down by water infiltrating
    through the A horizon, so often stained red by
    oxidation of iron minerals
  • C horizon made of weathered bedrock (parent
    material)
  • Usually contains larger particles and rock
    fragments
  • Bedrock the underlying rock that is still mostly
    un-weathered

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Soil Horizons
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