Shoreline Erosion and Deposition

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Shoreline Erosion and Deposition

• Where does sand come from?

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What images pop into your head when you hear the
word beach?

• Sand, blue ocean as far as the eye can see,
  balmy breezes, and waves.

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Shoreline

• Where land and a body of water meet
• Ocean, lakes, rivers

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Quick Review

• Erosion is the breakdown and movement of
  materials
• Deposition takes place when these materials are
  dropped

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Wave Energy

• Waves occur when wind moves over the ocean
  surface.
• Size of the wave depends on how hard and long
  (length of time) the wind is blowing
• Harder and longer the wind blows bigger the
  wave!
• Wind from storms produce large waves that cause
  shoreline erosion

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• Wave Trains

• Are waves that travel in groups.
• As waves travel away from their source they
  travel uninterrupted.
• Reach shallow water they break
• Ocean floor crowds the bottom of the waves
• Shortening the length while increasing the height
• Becomes too tall it topples over
• Known as the surf
• Wave period is the time interval between breaking
  waves
• Usually 10 20 seconds long

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Pounding Surf

• Breaking waves crash against the rocky shore,
  releasing their tremendous amounts energy!
• Breaks rock uses the broken rocks to further
  erode
• Rushing water washes into cracks dissolving
  minerals which further breaks down the solid
  rock
• Moves smaller particles of rock and sand to other
  locations forming beaches

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How does it Look?
Draw diagram
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Wave deposits

• Carry an assortment of materials
• Rock fragments
• Sand
• Shells

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Beaches

• Technical term
• Is any area of the shoreline made up of material
  deposited by waves.
• supplied from rivers
• eroded from nearby materials

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Wave angle makes a difference!

• Movement of sand depends on the angle at which
  the waves strike the shore causing the sand to
  migrate in a zigzag path

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How does it look?

• Most waves approach the beach at a slight angle
• Retreat in a direction more perpendicular

Draw diagram
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Offshore deposits

• Longshore Currents
• Is a movement of water near and parallel to the
  shoreline
• Pushes water along the shore
• Transports and deposits eroded materials offshore
• Creates offshore landforms
• Sandbars are an underwater or exposed ridge of
  sand, gravel, or shell material
• Barrier spit occurs when an exposed sandbar is
  connected to the shoreline

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Wave Erosion

• Wave erosion produces a variety of features along
  a shoreline
• Sea cliffs are formed when waves erode and
  undercut rock producing steep slopes
• Rate of erosion depends on the hardness of the
  rock and the energy delivered by the waves
• Granite erodes slowly
• Sedimentary rock erodes more rapidly

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• During storms and a high tide, waves deposit sand
  at the back of a sloping beach, forming a feature
  called a berm.
• Berms mark the highest point that waves reached
  during the last storm or high tide.
• While berms may obstruct beachfront views
  leveling them are not a good idea they prevent
  the erosion of inland soil ?

Is that a fact!!
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Berm
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Shaping the shoreline

• Most erosion occurs during storms
• Larger the waves more the energy released
• This energy is so powerful it can remove huge
  chunks of rock

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Coastal Landforms Created by Wave Erosion

• Sea stacks are offshore columns of resistant rock
  that were once connected to the mainland
• Waves have eroded the mainland, leaving behind
  isolated columns of rock

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• Sea stacks are common along Washingtons
  shorelines

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Sea Caves

• Form when waves cut large holes into fractured or
  weak rock along the base of sea cliffs
• Sea caves are common in limestone cliffs, where
  the rock is usually quite soft

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Sea Arches

• Form when wave action continues to erode a sea
  cave, cutting completely through the rock.

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Headland

• Is a finger-shaped projection that occurs when
  cliffs formed of hard rock erode more slowly than
  surrounding rock
• Hard rock will form headlands
• Softer rock will form beaches or bays

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Wave Cut Terrace

• Forms when a sea cliff is worn back, producing a
  nearly level platform beneath the water at the
  base of the cliff

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Review Questions

• Describe one way that waves shape the shoreline.
  Use examples as support.
• Explain how beaches form and why all beaches are
  not the same.
• Describe the way sand is moving along the
  shoreline.
• How many waves do you think reach a shoreline in
  a day if the wave period is 10 seconds? (Hint
  calculate how many waves occur in a minute, in an
  hour, and in a day.)
• Draw pictures for the various coastal landforms.