Water Erosion and Deposition

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Chapter 8

• Water Erosion and Deposition

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8.1 Surface Water

• Explain what causes runoff
• Compare rill, sheet, gully, and stream erosion
• Discuss the three different stages of stream
  development
• Describe how alluvial fans and deltas form

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8.1 Runoff

• Runoff
• water that does not soak into the ground or
  evaporate flows across the Earths surface
• Part of the water cycle Evaporation,
  condensation, precipitation, runoff, evaporation

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8.1 Runoff

• Factors affecting runoff
• The amount of rain
• The more rain, the more runoff
• The length of time
• Longer periods results in more runoff
• Slope of the Earths surface
• Steeper the slope the more runoff
• Amount of vegetation
• Less vegetation results in more runoff

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8.1 The Effects of Gravity

• Water will increase in speed by 9.8m/s
• As water moves down a slope the water picks up
  speed and energy
• Faster the water the more erosion occurs

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8.1 Water Erosion

• Rill and Gully Erosion
• Rill erosion
• Occurs when small streams form during periods of
  heavy rain
• Leaves behind a small scar on the Earths surface
• Over time rill erosion can become gully erosion
• Gully Erosion
• Occurs when a rill channel becomes broader and
  deeper
• More erosion occurs than with rill erosion

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8.1 Water Erosion

• Sheet Erosion
• Water falls on a broad flat area
• Water accumulates until it begins moving slowly
• Occurs when rainwater flows into lower
  elevations, carrying sediments

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8.1 Water Erosion

• Stream Erosion
• Stream water that continues to flow along a
  depression the water created
• Water moves sediments from the bottom and sides
  of the steam
• Stream becomes wider and deeper
• River stream wider than 12 feet

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8.1 River System Development

• River Systems
• Water in the river begins as precipitation that
  is transported through the following structures
• Sheet, rills, gullies, streams, rivers
• Drainage Basin
• The area that a stream receives its water
• Eventually the water reaches the main river that
  drains into the ocean
• Mississippi River basin is the largest U.S. basin

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8.1 Stages of Stream Development

• Streams are defined as being classified as
• Young
• Mature
• Old
• The stage is determined by the slope of the
  surface
• The actual age doesnt influence a streams
  classification

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8.1 Stages of Stream Development

• Young streams
• Steep sides
• May have whitewater rapids and waterfalls
• Found on steep slopes
• Usually straight and narrow
• Has a high energy level
• Erodes on the bottom more than the sides

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8.1 Stages of Stream Development

• Mature streams
• Flows less swiftly through its valley
• The energy begins to erode the sides
• Begin to curve due to the varying speeds of the
  water

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8.1 Stages of Stream Development

• Deeper water areas flow faster than shallow areas
  due to less friction
• Areas of faster water erodes the sides faster
  forming curves called meanders
• Areas where rocks are softer erode faster than
  the areas opposite the stream
• The broad flat valley floor is called a
  floodplain
• Usually covered by water when the stream floods

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8.1 Stages of Stream Development

• Old Streams
• Flows slowly through a broad, flat floodplain
• Little erosion occurs due to the slope of the
  stream
• River systems have streams of all ages

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8.1 Deposition by Surface Water

• Sediments are deposited when the water loses its
  energy
• Larger sediments settle out first
• Smallest sediments are last to settle
• Types of deposits
• Alluvial fans
• Usually found in at the base of a mountain valley
• Deltas
• The sediments are not deposited until it reaches
  the ocean

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8.2 Groundwater

• Describe the groundwater system
• Explain the effect that soil and rock
  permeability have on groundwater movement
• Describe ways that groundwater erodes and
  deposits sediments

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8.2 Groundwater System Development

• Water that soaks into Earths surface becomes
  part of the groundwater system
• Between each particle of weathered rock in the
  soil are spaces called pores

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8.2 Groundwater System Development

• Permeability
• Soil and rocks are permeable when water can pass
  through them
• The more pores present the more permeable the
  soil or rock
• The more easily water can move
• Clay has very few pores for water to travel
  through
• Clay is impermeable due to the lack of pores

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8.2 Groundwater System Development

• Groundwater Movement
• Water continues to move downward until it hits
  impermeable rock called bedrock
• Water begins to fill up the pores above the layer
• An aquifer may develop
• A layer of permeable rock that transmits water
  freely
• The area of all pores are filled with water are
  called the zone of saturation
• The upper surface is called the water table

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8.2 Wells, Springs, and Geysers

• Wells
• Water well hole drilled through the Earths
  surface until the water table is reached and a
  pump pumps water to the Earths surface
• Can go dry because water is removed faster than
  it is replaced

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8.2 Wells, Springs, and Geysers

• Artesian well a type of well that doesnt need
  a pump
• Requires a sloping aquifer between two
  impermeable layers
• Increases the pressure of the area
• Hole drilled in the surface can cause a fountain

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8.2 Wells, Springs, and Geysers

• Springs
• The area on Earths surface where the water table
  reaches the surface
• Water is usually cold, but can be hot

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8.2 Wells, Springs, and Geysers

• Geysers
• A hot spring that erupts periodically, shooting
  water and steam into the air
• Groundwater is heated to very high temperatures
  causing it to expand underground
• Some water is pushed out of the ground
• Remaining water boils quickly
• Steam flows out of the opening pushing the
  remaining water out with it
• Releases 40,000 liters (10,566 gal) once per hour

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8.2 Groundwater Erosion and Deposition

• Acidic groundwater can dissolve limestone
  underground just as it can above ground
• The space is dissolved over time until an
  underground opening is formed called a cave
• Cave Formation
• With erosion deposition must occur
• Water evaporates and leaves behind a small amount
  of deposits on the ceiling called stalactites
• Water drips to the floor evaporates and leaves
  behind deposits called stalagmites

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8.2 Groundwater Erosion and Deposition

• Sinkholes
• Underground rock near the surface is dissolved
• Eventually the surface cant support itself and
  collapses into the cave

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8.3 Water wars

• Give examples of ways people use water
• Explain why some communities must rely on water
  diversion for their water supply
• Identify a problem caused by water diversion

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8.3 Water as a Resource

• Average person uses 397 liters (105 gal) every
  day
• Some communities must transport their water over
  great distances to support their use

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8.3 Water as a Resource

• A bitter battle
• Water that is transported to new locations may be
  needed to fill up water resources for other
  communities or natural resources

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8.3 Two Points of View

• Conserve the natural resource
• Decreasing water levels in natural resources
• Increases the salt and mineral concentrations
• Could cause organisms naturally found in these
  areas to be killed
• Could lose the habitat organisms need to survive
  due to the lowered water levels

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8.3 Two Points of View

• Water needed by people
• Water needs to be diverted from natural areas to
  support human needs

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8.4 Ocean Shoreline

• Describe forces that cause shoreline erosion
• Compare and contrast different types of
  shorelines
• List some origins of sand

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8.4 The Shore

• Shoreline forces
• Surface waves constantly move sediments back and
  forth
• Waves are constantly eroding and depositing
  sediments
• Longshore currents
• Occurs when waves reach the shore at angles
• Causes water to run parallel to the shore

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8.4 Sandy Beaches

• Rocky shores are eroded by the waves crashing
  into them and the abrasion of the sediments being
  transported to form sand
• Beaches
• Deposits of sediments that run parallel to the
  shore
• Deposits could be made from seashell fragments
• Sand Erosion and Deposition
• Sand can be moved by humans and storms besides
  waves

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8.4 Sandy Beaches

• Barrier Islands
• Sand deposits that parallel the shore but are
  separated from the mainland
• Begin as a ridge of sand deposited by waves
• Hurricanes and other storms can increase the
  amount of deposits to sea level or above
• Wind blows the sand into dunes keeping it above
  sea level
• Can last a few years or centuries, but always
  temporary