Weathering and Erosion

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Weathering and Erosion

• Earth Processes
• Hill Science 6

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Weathering

• Weathering is the wearing or breaking of rocks
  into smaller pieces by water, temperature
  changes, wind, living things, or chemical
  changes.
• The fragments of rock stay in place.

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Weathering

• There are two types of weathering
• Mechanical weathering
• and
• Chemical weathering

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Mechanical Weathering

• The physical breakdown of rocks into smaller
  pieces, gradually reducing them to the tiny
  particles that make up soil.

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Agents of Mechanical Weathering

• Wind, water, gravity, glaciers - Abrasion
• Ice ice wedging
• Pressure change inside earth to surface of
  earth - exfoliation
• Temperature change alternating hot to cold -
  exfoliation
• Plants and animals organic activity root pry,
  animal burrowing

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Wind
Arches National Park, Utah, USA
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These rocks have been blasted by wind and sand
causing them to become rounded.
Type of Weathering? WIND ABRASION
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Water
The Grand Canyon created by the Colorado River
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Water
Friction and Repeated Impact
Type of weathering? Abrasion
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Glacial Action
Glacial ice will scour and abrade the surface it
slowly scraps over. Glaciers form broad U-shaped
valleys in their wake. What type of
weathering? Abrasion
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Exfoliation On Half Dome, the rock is peeling
away from the mountain in layers just like an
onion. This is called exfoliation which is caused
by the change in pressure when a rock that was
formed underground is thrust to the surface.
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Pressure Changes
Peeling of the surface of a rock due to pressure
change. What type of weathering? Exfoliation
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Temperature Changes

• Warm to cold and back again
• Splits rocks or peels off layers

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Temperature Change
Repetition of cooling and heating over and over
again. When might that happen? What type of
weathering? Exfoliation
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Temperature Changes

• Water to Ice
• Ice Wedging
• Heaving
• Glaciers

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Ice Wedging
Water fills a crack, freezes and expands making a
larger crack. This process repeats over and over.
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Ice wedging slowly breaks up this sedimentary
rock into unusual shapes.
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Frost Heaving
Repetitious freezing and thawing of water under
the patio causes the surface to heave when the
ice expands under the patio and contracts when
ice melts.
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Organic Activity
Plants What do you see happening here?
Root Pry
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Plant RootsThe action of plant roots is called
root pry
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Animal Activity- how does this cause weathering?
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Pictures of Mechanical Weathering

• Link to pictures
• Link to places

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Mechanical Weathering

• 1. Abrasion the wearing away of solid
  particles caused by wind, water, glacier ice,
  and gravity
• 2. Ice wedging - when water in a crack or hole
  in a rock freezes it expands making the opening
  larger. Melting moves it deeper into the opening
  and the process repeats Caused by the repeated
  thawing and freezing of water.

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Mechanical Weathering

• 3. Organic activity people, animals, or plants
  break up rock by digging or burrowing. Root pry
  the splitting of rock caused by the expanding
  root growing deeper.
• 4. Exfoliation flaking off of the surface of
  the rock caused by change in pressure from
  inside earth where formed to lower surface
  pressure or temperature change.
• 5. Heaving rocks shift and crack caused by
  repeated freezing and thawing

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Chemical Weathering

• Chemical weathering is the breaking down of rocks
  by changing their chemical composition.

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Agents of Chemical Weathering

• Acid precipitation - carbonation
• Acid from plants humic acids
• Oxygen - oxidation

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Water

• Carbonation - Water weathers rock by dissolving
  it

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Carbon Dioxide

• CO2 dissolves in rain water and creates carbonic
  acid
• Carbonic acid easily weathers limestone and
  marble (CaCO3)
• A cave may
• result
• Type of weathering?
• carbonation

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• Chemical Weathering
• Carbonation

Sinkhole
Stalactites and Stalagmites
Karst terrain
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Result of Rainwater Weathering
Type of Weathering? carbonation
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Humic AcidsAcid from Lichens Weathering Rock
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Living Organisms

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

Type of weathering? Humic acids
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Oxygen

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

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Oxygen Caused Chemical Weathering
Type of weathering? oxidation
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Chemical Weathering

• Carbonation-Acid precipitation - CO2 dissolves in
  rain water and creates carbonic acid which easily
  changes the chemical composition of certain rocks
  (limestone and marble)
• Humic Acids lichens and moss produce acids that
  break down the minerals found in rocks they are
  growing on
• Oxidation when oxygen combines with another
  substance to create an entirely new substance Fe
  O produces iron oxide (rust)

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Weathering and Erosion

•  Weathering and erosion are called external
  processes because they occur at or near Earths
  surface.
• Weathering and erosion are part of the rock
  cycle because they are responsible for
  transforming solid rock into sediment.
• So how do they differ?

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Weathering or Erosion?

• Weathering is the breaking of rocks into smaller
  pieces.
• Erosion is the moving of weathered sediments from
  one place to another.
• Erosion is the transportation of weathered
  material by the mobile agents of wind, water and
  glacial action (ice).

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Video Links

• Formation of the Grand Canyon
• Grand Canyon Lava Flows
• Ireland Glaciated Landscape

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Principal of Uniformity

• Belief that the processes that changed our world
  in the past are still in existence today and
  continue to change the earth.

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Chemical Weathering

• Chemical weathering is the breaking down of rocks
  by changing their chemical composition.

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Rates of Weathering
Chapter 10
Differential Weathering

• What Is Differential Weathering? Differential
  weathering is a process by which softer, less
  weather resistant rock wear away and leave
  harder, more weather resistant rock. The image
  below is an example of differential weathering.

Devils Tower, Wyoming
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Rates of Weathering

• What determines how quickly a rock will weather?
• Type of Rock (differential weathering) some
  rocks weather more quickly than others, due to
  composition or condition
• Pollution causes acid precipitation which will
  weather rocks more quickly
• Climate tropical fastest due to more moisture
  and plant action, deserts slowest due to lack of
  humidity
• Size smaller rock has more surface area to
  volume than a larger rock. More surface is
  exposed to weathering, so it will weather more
  quickly.

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Rates of Weathering
Chapter 10
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Chapter 10
Rates of Weathering
Weathering and Elevation

• High Elevations Rocks at higher elevations, as on
  a mountain, are exposed to more wind, rain, and
  ice than rocks at lower elevations.
• Steep Slopes The steepness of mountain slopes
  increases the effects of mechanical and chemical
  weathering. Steep slopes cause water and
  sediments to quickly run down the side of the
  mountain.

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Weathering Website

• Weathering animation click here
• http//www.uky.edu/AS/Geology/howell/goodies/elear
  ning/module07swf.swf