Erosion Or... How to make molehills out of mountains.
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Transcript of Erosion Or... How to make molehills out of mountains.
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ErosionErosion
Or. . . How to make molehills out Or. . . How to make molehills out of mountains.of mountains.
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What is Erosion?What is Erosion?
• Weathered rock particles (sediments) are transported through the process of erosion.
• Any process that moves sediments from one place to another is called erosion.
• Over time, erosion shapes and lowers Earth’s surface.
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Transporting Systems of ErosionTransporting Systems of Erosion
Several components:
• An agent of erosion such as: moving water, wind, ice, or human activity.
• The sediments being moved.
• A driving force.
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THETHE DRIVING FORCE DRIVING FORCE
• GRAVITY– Usually works together with water, wind or ice
to move sediments.– Can work on its own.
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Mass Movements (Wasting)Mass Movements (Wasting)
Slow mass wasting• Soil creep
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Rapid mass wasting• Rockfalls
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• Landslides
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• Mudflow
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• Slump
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Running WaterRunning Water
• Most common agent of erosion– Runoff
• Temporary – can carve out rills or gullies
– Streams and rivers• Permanent – confined to a channel
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Streams and RiversStreams and Rivers
• Carry sediments in different ways– Solution – dissolved minerals– Suspension – silts and clays– Bedload – largest sediments slide, roll, or bounce
along bottom
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Deposition and SortingDeposition and Sorting• A stream looses velocity when entering quiet
waters so its ability to transport sediment decreases. Particles drop to the bottom. This is deposition.
• Large particles settle first. Other particles settle according to size. Smallest particles (clay) drift the farthest and settle last. This is sorting.
Boulders
Cobbles
PebblesSand Silt Clay
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Rounded Sediments from AbrasionRounded Sediments from Abrasion
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LandformsLandforms
• YOUNG rivers create V-shaped valleys– Most energy
expended in downcutting
– Valley slope quite steep
– River gradient can also be quite steep
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• MATURE rivers broaden their valleys.– More energy expended
sideways– Valley slopes less steep– River gradient not as
steep
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• Rivers in OLD AGE have very broad valleys– Most energy
expended sideways– Has many meanders– River gradient almost
flat
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Erosion can create spectacular scenery.Erosion can create spectacular scenery.Crustal uplift and river erosion created the Grand Canyon over millions of years.
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Watershed or Drainage AreaWatershed or Drainage Area
• Often, rivers are fed by many tributaries over a large area. This is called a watershed.
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• The largest in the U.S. is the Mississippi River watershed. It drains 42% of the lower 48 states.
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The lower Mississippi River has a very broad valley with many meanders. Here, it is a river in old age.
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• Imagine trying to pilot a river boat through all of the meanders.
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Oxbow LakesOxbow Lakes
• Meanders are often cut off when a river floods. When this happens an oxbow lake is created.
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Where Erosion and Deposition Where Erosion and Deposition OccurOccur
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Flood PlainFlood Plain
• Rivers with broad valleys are prone to flooding.
• During flooding a river overflows its banks into the wider valley and deposits sediments forming a flood plain.
• Farmers often locate on flood plains because they have fertile soil for growing crops.
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• During times of severe flooding there is much property damage. Sometimes at a cost of many billions of dollars.
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DeltaDelta
• Where a river enters a quiet body of water its transported sediments deposit at the mouth. This is called a delta.
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River areas are diverse ecosystems that are River areas are diverse ecosystems that are inhabited by many species of wildlife.inhabited by many species of wildlife.
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