Weathering and Erosion

1
Weathering and Erosion

• Friday, May 18
• Monday, May 21

2
Agenda

• Weathering and Erosion lesson (30 minutes)
• Activity time (55 minutes)
• Clean up/Stamps (10 minutes)
• Points (5 minutes)

3
Weathering and Erosion

• Some of the most beautiful and interesting
  geologic features are caused by weathering and
  erosion.
• This canyon is an example of the effect of water
  on Earths surface.

4
Weathering

• There are two types of weathering physical and
  chemical.
• Physical (or mechanical) weathering breaks rocks
  into smaller pieces, but does not alter their
  chemical compositions.
• Chemical weathering breaks down rock by changing
  its chemical composition.

5
Physical Weathering

• Ice can break rocks.
• A common kind of mechanical weathering is called
  frost wedging or frost action.
• Water seeps into cracks or joints in rock and
  then freezes.
• When water freezes it expands, pushing rock
  apart.
• Every time the ice thaws and refreezes, it wedges
  farther into the rock.

6
More Physical Weathering

• Plants can also break rocks.
• The roots of plants can also act as wedges as the
  roots grow into cracks in the rocks.
• As the plant grows, the roots exert constant
  pressure on the rock, eventually causing pieces
  to break off.

7
Mechanical Weathering

• mechanical weathering

8
Chemical Weathering

• chemical weathering

9
Chemical Weathering

• Some minerals react with oxygen, forming oxides
  called oxidation.
• Red sedimentary layers in Badlands National Park
  contain iron that has reacted with oxygen to form
  hematite.

10
Chemical Weathering

• Carbon dioxide can cause chemical weathering.
• Carbon dioxide can react with water in the air to
  form carbonic acid. This weak acid reacts with
  some minerals.
• Minerals dissolved by carbonic acid may be washed
  away, leaving underground pockets, or caves.

11
Water and Chemical Weathering

• Water plays a key role in chemical weathering.
• Some minerals react with water, which changes
  their physical properties. This is called
  hydrolysis.
• Some minerals dissolve in water and are carried
  to new locations.

12
Chemical Weathering

• Carbonic acid dissolved the calcite in the
  sedimentary rock limestone to produce this
  underground cave.

13
Acid Rain

• Acid precipitation can slowly dissolve minerals.
• Sulfur dioxide and nitrogen oxides enter the air
  as a result of burning fossil fuels.
• These chemicals can react with water in the air,
  forming sulfuric acid, nitric acid, or nitrous
  acid.
• When this happens, the precipitation that results
  is acidic.
• Acid Rain Control Program required power plants
  to reduce the release of sulfur dioxide, which
  has reduced the acidity of rain.

14
Acid Rain

• Acid rain weathers stone structures like this
  marble statue in Brooklyn, NY.

15
Erosion

• Erosion a process in which the materials of the
  Earths surface are loosened, dissolved, or worn
  away and transported from one place to another by
  a natural agent, such as wind, water, ice, or
  gravity
• Deposition the process in which material such as
  sediment is laid down, or deposited as a result
  of erosion

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Erosion

• Erosion is caused by
• Wind
• Water
• Ice
• Gravity
• erosion

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• Deltas, such as this one in New Zealand, are
  forrmed by deposition.

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Erosion Shapes Earths Surface

• Water is the most effective physical weathering
  agent.
• Rivers carry sediment to the ocean, and create
  canyons and riverbeds.
• The faster the water flows, the larger the
  sediment it can carry.

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• Oceans also shape Earth.
• Waves crash onto shores, shaping the land.
• Ocean waves can create tall cliffs and jagged
  coastlines.

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• The action of waves slowly tearing away the
  rocky coast formed the Cliffs of Moher.

21

• Glaciers erode mountains.
• Large masses of ice can exert tremendous forces
  on rocks.
• Moving glaciers grind rocks below them into fine
  powder.
• Glacial meltwater streams carry the sediment away
  from the glacier.

22

• This glacier in Alaska has slowly pushed its way
  through these mountains
• Glaciers can carve U-shaped valleys in mountains

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• Wind can also shape the landscape.
• Fast moving wind can carry fine sediment.
• Sediment carried by wind can smooth Earths
  surface and erode the landscape.

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• Wind erosion can play a part in forming sandstone
  arches

25
Geology of the PNW

• ancient megaflood