Weathering%20

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Weathering Physical and Chemical
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Weathering

• Weathering is the wearing away of rock and can be
  chemical or physical.
• Physical weathering the process by which rock
  is broken down into smaller pieces by physical
  means.
• Chemical weathering - the break down of rocks by
  chemical means

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Physical Weathering

• Process by which rocks are broken down into
  smaller pieces by physical forces.
• Types of Mechanical weathering
• Abrasion
• Temperature changes (freezing and thawing)
• Ice or Frost wedging
• Plant roots
• Burrowing of animals (animal action)

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Abrasion

• Abrasion is weathering by grinding action This
  is physical weathering
• These mountains in Costa Rica were mechanically
  weathered by abrasion.

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These mountains in Salt Lake City, Utah, were
also weathered by abrasion.
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Freezing and Thawing (temperature changes)
A rise in temperature causes rock to expand. A
decrease causes rocks to contract. This repeated
change weakens rocks, causing them to crumble.
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Ice or Frost Wedging
Water enters the cracks in rocks and freezes,
causing the cracks to expand. This process will
eventually break even the biggest rocks.
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Plant Roots

• This happens as these small roots grow into small
  cracks, as the tree grows and the roots get
  bigger, they will eventually break the rock.
• Think about how plants and weeds will grow in the
  smallest crack of a sidewalk. Also think about
  seeing tree roots that crack the sidewalk in
  older neighborhoods with large trees.

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Animal Action (Burrowing)
Many dig burrows in the ground. Examples are
squirrels, prairie dogs, ants and earthworms.
As animals move soil, it exposes rocks, these
rocks then experience weathering.
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Chemical Weathering

• the process that breaks down rock through
  chemical changes.
• The agents of chemical weathering
• oxygen- combines with iron to form rust
  (oxidation)
• Acid precipitation (rain)
• Acids in ground water
• Acids in living things

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Oxygen

• Iron combines with oxygen in the presence of
  water in a processes called Oxidation.
• The product of oxidation is rust.

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Acid Precipitation or Rain

• Compounds from burning coal, oil and gas react
  chemically with water forming acids.
• Acid rain causes very rapid chemical weathering.

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Water

• Ground Water weathers rock by dissolving it.
• CaCO3 2CH3COOH Ca(CH3COO)2 H2O CO2.
• Read more http//www.ehow.com/info_7888211_vineg
  ar-affect-limestone.html
• The dissolved rock is carried by water and later
  deposited.
• Examples are Stalactites and stalagmites

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Living Organisms

• Lichens and mosses that grow on rocks produce
  weak acids that chemically weather rock.

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2 factors that determine the rate of weathering

• Rock Type - Rock that is permeable (has holes in
  it), weathers faster than rock that is
  impermeable.
• - The mineral content of rock also determines
  how fast a rock weathers.
• Climate - Rock weathers faster in warm, humid
  climates.

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Erosion

• Erosion is the movement of sediment by water,
  wind or ice.
• In this picture taken in Oregon, a gully has been
  created by a stream that has cut a path through
  soft sediment after a strong rainfall.

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Erosion

• Erosion has caused this bank in Squaw Creek to be
  cut away by the weathering of the river, forming
  a landform that simulates a partial cave on the
  left side of this picture.

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Erosion

• Here, erosion by longshore drift, has caused a
  lagoon to form along this beach in Costa Rica.

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Deposition

• Deposition is the
• adding of sediment in
• an area as it settles
• out and forms new
• landforms. In this
• picture, taken in
• Squaw Creek, near Sisters, Oregon, rocks have
  been deposited along the bank of the river after
  heavy rains.

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Deposition

• In this picture, also taken in Squaw Creek, a
  sandbar has been formed by sediment that has been
  washed down the river. This might also be
  considered a spit.

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Deposition

• In this picture, salt has been deposited in the
  Great Salt Lake, Utah. You can see the salt
  deposits. They appear as white areas on the edge
  of the water.

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Landforms

• http//www.classzone.com/books/earth_science/terc/
  content/visualizations/es1205/es1205page01.cfm?cha
  pter_novisualization

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Erosion Control Methods

• These native plants were left undisturbed on the
  beach in Costa Rica, so that they would hold in
  the sand and prevent erosion on the beach. This
  is an example of permanent erosion control.

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other examples of erosion control
silt fencing
terracing
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River Formation

• A river is a natural stream of freshwater that is
  larger than a brook or creek. Rivers are normally
  the main channels or largest tributaries of
  drainage systems. Typical rivers begin with a
  flow from headwater areas made up of small
  tributaries, such as springs. They then travel in
  meandering paths at various speeds. Finally, they
  discharge or flow out into desert basins, into
  major lakes, or most likely, into oceans.

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Erosion and Deposition

• Meanders are formed by the weathering of one bank
  of a river and the deposition of the weathered
  sediment on the opposite bank of the river. This
  creates a loop-like bend in a river, such as this
  one. This view was taken from an airplane over a
  mountain range in the midwest.

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changes in a meandering river

• http//www.classzone.com/books/earth_science/terc/
  content/visualizations/es1306/es1306page01.cfm?cha
  pter_novisualization
• formation of an oxbow lake
• http//www.cleo.net.uk/resources/displayframe.php?
  src309/consultants_resources2F_files2Fmeander4.
  swf

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• The world's longest river is the Nile River in
  Africa, which runs 4,187 miles (6,739 kilometers)
  from its source in Burundi to the Mediterranean
  Sea.

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• Every river has a point of origin- it is the
  highest point in the water basin.
• Gravity- is important rivers almost always flow
  downhill watercourse.
• Some rivers start from springs, especially in
  humid climates. Springs occur as groundwater
  rises to Earth's surface and flows away.
• Other rivers originate from lakes, marshes, or
  runoff from melting glaciers located high in the
  mountains. Some rivers have their beginnings in
  huge glaciers.

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(STOP) LESSON 3Steps to River Formation

• 1) Precipitation (rainwater or snow ) is the
  source of the water for most rivers.
• 2)When a heavy rain falls on ground that is
  steeply sloped or is already saturated with
  water, water runoff trickles down Earth's surface
  rather than being absorbed- this is called
  surface runoff.
• 3) After it travels a short distance, the water
  begins to run in small parallel rivulets called
  rills.
• 4) As these rills pass over fine soil or silt,
  they begin to dig shallow channels, called
  gullies. This is the first stage of erosion. A
  gully only has water in it when it rains.
• 5) A stream is formed when gullies join together.
  It is a channel along which water is continually
  flowing down a slope. Streams rarely dry up.
• 6) A stream grows larger as it gets water from
  tributaries. A tributary is a stream that flows
  into a larger stream.

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Visual steps to river formation
Rills
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gullies
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River System
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Notes quiz

• 1. Examples of mechanical weathering are
• ice wedging, animal actions, oxidation
• plant growth, ice wedging, abrasion
• freezing and thawing, burrowing, acid rain
• 2. Examples of chemical weathering are
• a) acid rain, oxidation, plant roots
• b) freezing and thawing, animal actions,
  oxidation
• c) burrowing, carbon dioxide, abrasion

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• 3. Deposition is
• the movement of sediment or rock
• the settling out of sediment or rock
• the breaking down of sediment or rock
• 4. A meander is
• a) a small river that runs into a larger river
• b) a loop-like bend in a river
• c) a lake that has been cut off from a river

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• 5) Name 3 methods of erosion control
• a)
• b)
• c)
• 6) What are 2 factors that affect the rate of
  weathering?
• a) ______________________
• b) ______________________
• 7) What is surface run-off?

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• 8) Rills in soil run together to form __________
  that only have water in them when it rains.
• 9) What forms when gullies join together?
• a) a rill
• b) a stream
• c) a tributary
• 10) What is the original source of water of most
  rivers? (1st step in river formation)