Stream Deposition

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Stream Deposition

• Deposition in water

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Ready? Set? Go!

• Remember Deposition? That step of the rock cycle?
  Yeah were talking about that

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New Vocabulary

• You dont need to copy these down, wait until we
  get to them!
• Deposition
• Alluvium
• Delta
• Alluvial fan
• Flood plain
• Ground water
• Water table
• Aquifer
• Porosity
• Permeability

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Streams and River Depositions

• Deposition is the process by which material is
  dropped, or settles.
• In terms of stream deposition, we are often
  talking about the dirt and silt in a streams
  load.
• Think about puddles during a rainy day and
  after the rain has stopped for a while. Do you
  notice the puddle becomes clear with a layer of
  mud at the bottom after the rain stops? But
  while it is raining the puddle is often cloudy?
  Thats deposition!

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Deposition in water

• After rivers erode rock and soil, they deposit
  the rock and soil downstream. Rock and soil
  deposited by streams is called alluvium.
• Alluvium occurs where the speed of the currents
  in the river DECREASE.

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Deposition by streams

• Currents also slow when streams empty into large
  bodies of water (like the ocean). Much of the
  rivers load may deposit here and form a delta.
• A very famous delta is the Nile Delta at the
  mouth of the Nile River.

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Deltas versus Alluvial Fans

• When a stream empties onto a flat land (like a
  stream from mountain runoff), it wont form a
  delta but instead an alluvial fan. Alluvial fans
  have the same shape of a delta like a giant fan
  but form on dry land instead of connected to a
  large body of water.
• Deltaempties into a large body of water
• Alluvial fan empties into a flat dry area

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Flooding

• During periods of high rainfall or rapid
  snowmelt, an increased amount of water will lead
  to flooding of the surrounding river bank. When
  this happens, the land that becomes overflowed is
  referred to as a flood plain.
• A well known flood plain occurred around the
  Mississippi River and Missouri Rivers when they
  flooded the land in between them. (see pg 257)

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Water Underground?!

• Thats right!
• Simply put, there is a lot of water located
  within the rocks below the Earths surface. This
  water is referred to as ground water.

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Where can I find ground water?

• Ground water occurs in the zone of saturation.
  This is the area where spaces between rocks are
  filled with water. Above the zone of saturation
  is the zone of aeration (aero means AIR). The
  term water table is the boundary between the two
  zones.
• Real life connection When new buildings are
  being built on land, there is almost always a
  geologist who goes out to find the depth of the
  water table. This prevents the house from
  sinking! Did you know that some of the hotels
  in Las Vegas sink 2-3 inches a year because they
  didnt check the water table before
  construction?!?!

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Water between rocks?

• Within the zone of saturation (the zone where
  water and rocks hang out together), there are
  types of rocks that can hold large quantities of
  water. A rock layer that stores and allows the
  flow of ground water is called an aquifer.
• (aqua means WATER)

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What makes an aquifer?

• There are two characteristics
• A rocks porosity- or the amount of open space
  between individual rock particles.
• A rocks permeability- or the ability to let
  water pass through it.
• An aquifer requires porous rocks and permeable
  rocks.

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What now?

• Point Source Pollution- Point source pollution
  comes from one location which can be identified.
• Non point source pollution- Comes from many
  locations and is more dangerous because it cant
  be traced (or located).