Weathering

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Weathering

• Earth Science
• Chapter 5

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Mechanical weathering

• physical forces break rock into smaller pieces
  without changing the rocks composition
• 3 processes
• Frost wedgingwater seeps into cracks in rock and
  freezes force of water expanding breaks rock
• UnloadingRock overlaying an igneous formation is
  eroded reduced weight pressure causes top of
  igneous formation to expand and crack

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Frost wedging near hidden falls, Grand Teton
National Park
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Classic sheeted granite along the Tioga Road,
Yosemite National Park. The granite is broken
into gently dipping plates by unloading joints.
Unloading joints probably form as the rock is
exposed by erosion. These joints, and others that
are more steeply oriented, provide pathways for
water to enter the rock.
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This is Mt. Brewer, part of the Sierra Nevadas.
Looks like a huge hunk of rodk..
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This is the slope of the previous mountain.
Frost wedging has created huge boulders on the
sides of the mountain. The east ridge of Mt.
Brewer (the easy way up), near the summit. This
mountain, like most in the Sierra, is covered by
a thick layer of sharp-edged boulders produced by
frost wedging. Frost wedging is well-developed
here because the temperature cycles across the
freezing point many days each year.
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• Exfoliationslabs of rock breaking off in thin
  layers . A very good example of this is Stone
  Mountain outside Atlanta.

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• Biological activitygrowing plant roots, animal
  burrows human activity, etc.

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• Chemical weatheringtransformation of rock into
  one or more new compounds
• Water is the most important agent of chemical
  weathering.
• Mixes with carbon dioxide to form carbonic acid.
• Reacts with many common minerals

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• Rate of weathering is affected by rock
  characteristics and climate.
• Rock compositiongranite is resistant marble
  weathers easily
• Climatetemperature and moisture have strong
  affect and freeze thaw cycles, vegetation, etc.

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• Keep in mind by breaking a rock into smaller
  pieces the surface area is increased, exposing
  more surface area to chemical weathering.

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• Frost wedging is common in the mountains. Rock
  that has wedged loose may accumulate in piles
  called talus.

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• Soilpart of the regolith that supports plant
  life.
• Regolithlayer of rock and mineral fragments.

regolith
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• 4 components of soil
• mineral matter broken down rock
• humus (organic matterdecayed remains of
  organisms like plants)
• air
• water

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• Soil texture is based on the percentage of clay,
  silt, and sand.
• Texture strongly influences a soils ability to
  support plant life.

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• Important factors in soil formation
• Parent materialsource of mineral matter
• Timethe longer the soil has been forming, the
  thicker it is
• Climatehas greatest effect on soil formation
  hot wet forms thicker soil
• Organismsplants, animals, and microorganisms
  contribute to soil fertility and aeration
• Slopesteep slopes have thinner soils

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• Soil profilevertical column of soil which shows
  all soil layers
• Soil horizonslayers of soil with identifiable
  characteristics
• A horizontopsoil mostly organic matter,
  insects, and microorganisms
• B horizonsubsoil contains fine clay particles
  washed out of the A horizon
• C horizonpartially weathered parent material

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• Rates of soil erosion are affected by human
  activities that remove vegetation.

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• Mass movementthe transfer of rock and soil
  downslope due to gravity
• Most landforms are forms by a combination of
  weathering and mass movements

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• 4 triggers
• Watersaturates surface materials by heavy rain
  or rapid snow melt lubricates particles so they
  move easier
• Oversteepened slopesa slope remains stable only
  up to 25-40 degrees based on particle type size
• Removal of vegetationplants stabilize slopes b/c
  roots bind soil regolith together w/o plants
  soil moves easily
• Earthquakescan dislodge huge amounts of rock and
  unconsolidated material

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• Types of Mass Movements are based the kind of
  material that moved, how it moved, and the speed
  of movement

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• Types of Mass Movements
• Rockfallrocks freefall through air
• Rockslidea block of rock and loose material
  moves suddenly along a flat, inclined surface
  common in high mountain areas fastest moving
  mass movement (200 km/hr)

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• Slumpdownward movement of material on a curved
  surface does not move fast or far
• Flowmovement of material containing a large
  amount of water moves like a thick liquid (think
  cake mix).
• Mudflowmoves quickly
• Earthflowmoves slowly
• Creepcaused by alternating expansion
  contraction of the ground (freeze/thaw) slowest
  mass movement (1mm-3cm/yr) cannot be directly
  observed

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