The Work of Waves

1
The Work of Waves
2
How do West and East Coasts Differ?
Atlantic
Gulf Coast
Why?
Differences in The landscape next to the ocean
3
What Causes Waves?
Wind
Push
Drag
4
How Does Water Move in Waves?

• Wave form moves forward
• Water particles move in circular orbits

5
What is the Depth of the Wave Base?

• Wave base half a wave length
• If wavelength 400 feet
• Wave base 200 feet

6
Why Do Waves Break?

• As waves approach the shore they feel bottom
• Wave length shortens
• Wave height increases
• Circular motion ceases and wave falls forward

7
What is a tsunami?

• A giant wave generated by movement of the sea
  floor
• Generated by earthquakes or volcanoes
• Tsunami waves reach heights of 50 feet near the
  shore
• Travel up to 600 mph

8
Why Are Tsunami Hazardous?

• Tsunami pile up in shallow water
• Drown coastal property

9
How Do Waves Behave As They Approach the Shore?
10
Why Are Waves Refracted as They Approach the
Shore?

• Waves slow down and bend in shallow water off
  headlands
• Faster waves continue into the bay

11
What is the Effect of Refraction on a Coastline
of Headlands and Bays?

• Wave energy erodes headlands
• Sediments eroded from headlands are deposited in
  bays
• Erosion straightens shoreline

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Western Side of North America Coastline of
Headlands and Bays

• At end of ice age, rising sea level drowned river
  valleys and formed bays
• Higher land forms headlands
• Waves attack headlands and form cliffs

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How Do Waves Erode?

• Hydraulic Action
• Abrasion
• Solution
• Attrition

14
Softer rock form caves

• Caves form as waves erode weak rock
• Caves develop into arches
• Stacks form when arches collapse

15
Cave Erode to Form arches
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Changes Along a Shore

• 1890
• 1920
• 1970

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Point Reyes
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Coastline of Headlands and Bays
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Where Does Most Beach Sand Originate?

• Rivers flowing down to the sea
• Some erosion of cliffs

20
Why Does Sand Get Moved Along a Beach and in the
Surf Zone?

• Most waves approach the coast at an oblique angle
• Swash and backwash move sand up and down the
  beach in a zig-zag pattern
• Longshore currents form in the surf zone
• Currents move sediment parallel to the shore

21
What Coastal Features Are Formed By Longshore
Currents?

• Longshore currents transport material across bays
• Sandspits form across the open water of the bay
• Eventually, sandspits grow across the bay to form
  a baymouth bar

22
Is There More Sand on the Beach at the end of the
Summer or Winter?
A
B
End of Summer
End of Winter

• Which picture represents the end of the summer?
• Gentle summer waves build up the beach
• Plunging winter storm waves erode the beach

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Barrier Island Beaches
Barrier island coasts develop where there are

• Coastal plains next to the sea
• Gentle offshore gradients
• Slight tidal ranges

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Barrier Beaches Dominate the Atlantic and Gulf
Coasts

• Low-lying barrier islands are vulnerable to
  hurricanes
• Should be left undeveloped

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How Do Dams Affect Beaches?

• Less sediment reaches the beach
• Waves attack cliffs
• Cliffs are eroded

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What Are the Problems Presented by Sea Walls?

• Sea walls built to protect coastal property
• Waves bouncing back from sea walls erode sand
  away from the beach

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• Beach erosion continues after building on the
  shore

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Santa Barbara Harbor
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Groins
What is the direction of longshore transport
along this coast?
31
Can you tell the direction of longshore transport
along this coast?
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Do you know your rivers and lakes?
33
Breakwaters
Breakwaters on Lake Erie
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Artificial Beach Nourishment

• Ocean City, Maryland
• Note wider beach on left
• Pipeline pumps sand collected offshore

35
Identify these Coastal Features

• A
• Tombolo
• B
• Seacliffs
• C
• Sandspit
• D
• Stack

36
Is America losing its beaches?
37
What is this?

• A stack