Weathering, Erosion,

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Weathering, Erosion, Depositionpart 1
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Part I. Weathering

1. Weathering is the physical or chemical break-down
   of rocks or minerals at or near the earths
   surface - Breaking rock into pieces
2. ONLY rocks at the surface can weather
3. Types
4. Physical breaking rocks w/o changing
   composition
5. Chemical breaking rocks by chemically changing
   the minerals

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Chemical Weathering Agents

• Water dissolves certain rocks (salt)
• Air
• Oxidation (rusting) O2 combines w/ water and
  reacts with minerals containing iron
• CO2 combines w/ water to make carbonic acid,
  dissolves limestone
• Plants lichens make acid that dissolves rock

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Chemical Weathering Agents
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Oxidized rocks in Utah
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Carbonic acid at work!
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Sink hole
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Hydrolysis of feldspar
Clay forming from hydrolysis of feldspar
Feldspar
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Acid rain at work!
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Review of chemical weathering

• Oxidation (rust)
• Acid rain
• Carbonic acid
• Water Carbon dioxide ? Carbonic acid
• Water dissolving rocks with acids mixed in it
• Hydrolysis-water reacting with rock causing
  chemical change
• feldspar water clay

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Physical Weathering

• Frost action
• Water enters cracks in rocks, as it freezes it
  expands breaking the rock

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Physical Weathering

• Abrasion
• Grinding, rolling scraping of rocks together.
  Breaks off sharp edges, rounding the rock
• Caused by running water, waves, wind and glaciers

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Physical Weathering

• Plant action
• Plant roots work into rocks breaking the rock
  apart as it grows

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Physical Weathering

• Exfoliation
• Peeling off the outer layers of rock.
• Caused by repeated heating or cooling

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Review of physical weathering

• Frost action-alternating temperatures above and
  below freezing causes rock to crumble
• Abrasion-the physical grinding of rocks along a
  surface
• Root action -roots break a part land as they grow
  into the ground
• Burrowing animals
• Exfoliation-peeling of rock layers due to crustal
  unloading

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Exfoliation examples
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Abrasion
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Frost action at work!
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Root action
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Burrowing animals
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Factors Affecting Weathering

• Climate
• Hot, dry climate very little weathering
• Warm, moist climate rapid chemical
• Cold, moist climate strong frost action

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Factors Affecting Weathering

• Type of Rock
• Igneous and Metamorphic react SLOWLY, more
  dense
• Sedimentary weather rapidly

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Factors Affecting Weathering

• Particle Size
• As rocks break into smaller pieces, it weathers
  faster (more surface area exposed)

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Review Factors affecting rate of weathering

• Exposure to the elements
• The closer a rock is to the earths surface, the
  more weathering will occur
• Particle size
• When the rock particles are smaller, the rate of
  weathering increases
• Mineral composition
• Some minerals are more resistant to weathering
  than others
• Climate
• Warm, moist climates? chemical
• Cold, dry climates? physical

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SOILS

• Soils are a mixture of rocks, minerals and
  organic material

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Soil

• Final product of weathering
• Soil composition
• Inorganic material pieces of weathered rock
• Humus organic material from decayed plants and
  animals provides nutrients for growth

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Classes of Soil

• Soil Types
• Residual Soil
• Soils that stay where they are formed
• Soil composition matches the rocks underneath,
  granite rock granite in soil
• Transported Soil
• Soils that were carried to other locations
• Soil does NOT match, granite rock NO granite in
  soil

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Soil development depends on

• Climate
• Biological activity
• Slope of the land
• Time

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Soil profile
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Know this profile!
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Porosity and permeability of soils

• Porosity- amount of open spaces within soil
  particles

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• Permeability- amount of water that passes through
  a soil

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Weathering, Erosion, Depositionpart 2
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Part 2 - Erosion

• Carries away pieces from weathering
• Most soils are different from bedrock under them
  (transported soils)
• Gravity is MAIN force behind erosion

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What does erosion mean?

• Transport of weathered material.
• Agents of erosion are wind, water, ice
  (glaciers) and gravity.
• Water is the most common erosional agent

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Mass movement notes

• What comes up, must come down!

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What is mass movement?

• Mass movement When gravity pulls geologic
  materials down slope
• Driving force? gravity
• Resisting force? friction

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Soil creep



Velocity Less than 1 cm/year
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Debris flow
Velocity1 mm/day to 1 km/hour
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Mud flow
Velocity1-5 Km/hour
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Rock falls
Velocity Greater than 4 km/hour
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Conclusion

• Mass movement is the downward movement of rock,
  snow, soil and ice as a result of gravity.
• When the driving forcegtresisting force slope
  failure occurs
• Order of increasing speed
• soil creep?debris flow?mud flow?
• rock fall

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Agents of Erosion

• Gravity (Review)
• Landslides rapid movement of rock material down
  hill
• Slumping small landslides
• Creep VERY slow mvmt of material
• Talus piles of rock found at base of very steep
  slopes

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Agents of Erosion
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Agents of Erosion
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Agents of Erosion

• Wind
• Carries fine grained sediments about 1 meter
  above ground
• Grains are lifted and bounced along
• Wears away rocks at the base
• Dunes piles of wind blown sand

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Agents of Erosion
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Agents of Erosion
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Agents of Erosion

• Glaciers
• Masses of frozen water on ground
• Valley (alpine) glaciers
• rivers of ice
• Found at high altitudes in mountains

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Agents of Erosion

• Continental glaciers
• Large sheets of ice covering large areas of
  surface (Greenland, Antarctica)

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Agents of Erosion

1. Formed in areas where snow does not melt, keeps
   building up and is compacted into ice
2. As Ice builds up, pressure increases at bottom,
   causing ice to flow (cm to m per day)

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Agents of Erosion

1. As glaciers move, they carry materials of ALL
   sizes (sand to boulders)
2. Materials carried cause bedrock under glacier to
   be gouged and scraped

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VIII. Agents of Erosion
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Agents of Erosion

• Glacier Landscapes
• U-shaped valleys
• UNSORTED rock material when glacier melts (till)
• Drumlins groups of long oval hills
• Eskers winding ridges formed in tunnels under
  ice
• Kettles large piece of ice breaks off glacier
  making a hole, ice melts leaving the hole.
  Kettle lake hole is filled with water (Beaver
  Lake)

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Agents of Erosion
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VIII. Agents of Erosion
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The Hydrologic (Water) Cycle
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Water table
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Agents of Erosion

• Running Water
• MOST important (moves most material)
• Ways of carrying sediments
• Solution dissolved materials (salt)
• Suspension very fine particles (silt) suspended
  in water, looks muddy
• Bouncing pebbles bounced along stream
• Rolling and sliding largest particles moved
  without being lifted
• Particle Transport

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Agents of Erosion

• Velocity
• Speed of the water flow
• Depends on slope and volume (stream discharge)
• Greater slope greater velocity
• Greater volume greater velocity

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Agents of Erosion

• Sediments Carried
• Size
• FAST streams can carry LARGER sediments
• Quantity (amount)
• MORE volume carries MORE sediment
• Even though a fast moving stream can carry larger
  rocks, a slow moving stream with greater volume
  can carry more sediment (Mississippi River)

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How fast does a stream need to be flowing to
carry a cobble?
About 190 cm/sec
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What kind of particle can a stream carry if it is
going 400 cm/sec?
Boulder
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How fast does a stream need to be flowing to
carry a 1.0 cm particle?
50 cm/sec
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Agents of Erosion

• Effects of moving streams
• Carry sediments
• Deepen and widen stream bed as it drags and
  carries its sediments
• Abrasion happens (rocks becoming rounded)

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Agents of Erosion

• Stages of Stream Development
• Youth
• Steep gradients
• Rapid downcutting (carries rocks and pebbles)
• V shaped valley
• Has waterfalls or rapids
• Straight path

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Agents of Erosion

• Mature
• Less steep, less velocity
• Wind around obstructions forming loops
• Carries silt and clay (no rocks)
• Larger volume more sediment than youth

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Agents of Erosion

• Old
• Very small gradient
• Only carries finest sediments
• Can flood
• Makes Oxbow Lakes

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Agents of Erosion
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Agents of Erosion

1. Old streams can become young again if the area is
   uplifted and gradient becomes steeper
2. Most streams have youth at source, mature in
   middle and old age at their mouth (where river
   dumps into a lake/ocean)

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Weathering, Erosion, Depositionpart 3
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Part 3 - Deposition

1. Sediments are released or dropped from the agent
   of erosion

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Factors Affecting Deposition

• Size
• Large particles settle the fastest

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Factors Affecting Deposition

• Shape
• Round particles settle faster than flat particles
• Density
• More dense particles settle faster

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Sorting of Sediments

• Graded bedding (vertical sorting)
• Happens at ocean bottoms or landslides

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Sorting of Sediments

• Horizontal Sorting
• Large particles settle first as a stream enters a
  body of water

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Glacial Deposits

• Till
• Dropped from glacier.
• UNSORTED!!!!! (all sizes mixed)
• Outwash material
• Deposited from meltwater
• SORTED

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Energy Changes

• Kinetic Energy energy of movement
• Potential Energy stored energy
• High velocity High KE erosion
• Low velocity Low KE deposition
• Streams slow when
• Slope or volume decreases
• Moves into a body of water
• On the inside of a curve

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Energy Changes

• Streams have GREATEST PE at their source (highest
  point)
• Loses PE as it turns to KE on the way down

Greatest PE, Less KE
Greater KE, Less PE
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Erosion Deposition System

1. Side View (profile)

Source
Erosion Dominates water moving fast
Deposition river slows down
Mouth
Delta can form
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Erosion Deposition System

1. Top View

Inside of curve, water moves SLOWER, deposition,
shallow
Outside of curve, water moves FASTER, erosion,
deeper water
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Velocity within a Stream

1. Water moves fastest in the middle towards the top
   of the stream (less friction)

D Water moves fastest, smallest friction
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Velocity within a Stream

1. Cross Section of a Stream Corner

Outside Faster More Erosion Deep
Inside Slower More Deposition Shallow
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Velocity within a Stream
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Effects of Climate on Landscape

• Humid (wet)
• Worn down and rounded (more weathering)
• Arid (dry)
• More angled, sharper edges

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Effects of Climate on Landscape
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Drainage Patterns

1. Arrangement of streams draining water in an area
2. Determined by type of bedrock