Peralta Colleges, Physical Geography
Rita D. Haberlin, Instructor
WAVES AND COASTAL LANDFORMS
PowerPoint Presentation Outline Notes
The Work of Waves
What Causes Waves?
How Does Water Move in Waves?
- Wave form moves forward
- Water particles move in circular orbits
What is the Depth of the Wave Base?
- Wave base = half a wave length
- If wavelength = 400 feet
- Then wave base = 200 feet
Why Do Waves Break?
- As waves approach the shore, they feel bottom
- Wavelength shortens
- Wave height increases
- Circular motion ceases and the wave falls forward
What Is A Tsunami?
- A giant wave generated by movement of the sea floor
- Movement caused by earthquake or volcanic activity
- Tsunami waves reach heights of 50 feet near the shore.
- Tsunami waves travel up to 600 mph.
Why Are Tsunamis Hazardous?
- Tsunamis pile up in shallow water
- Drown coastal property
How Do Waves Behave As They Approach The Shore?
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
What Is The Effect of Wave Refraction On a Coastline Of Headlands and Bays?
- Wave enery erodes headlands.
- Sediments eroded from headlands are deposited in bays.
- Erosion erodes and straightens shoreline.
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.
How Do Waves Erode?
- Hydraulic Action
Caves Form In Softer Rock
- Caves form as waves erode faults and weak rock.
- Caves develop into arches.
- Stacks form when arches collapse.
Changes Along a Shore
Coastline of Headlands and Bays
Where Does Most Beach Sand Originate?
- Rivers carrying sediment to the sea.
- Erosion of headlands
Why Does Sand Move 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 sediments parallel to the shore.
What Coastal Features Are Formed By Longshore Currents?
- Longshore currents transport sediments across bays.
- Sandspits form across the open water of the bay.
- Eventually, sandspits grow across the bay to form a baymouth bar.
Barrier Island Beaches
Barrier island coasts develop where there are:
- Coastal plains next to the sea
- Gentle offshore gradients
- Slight tidal ranges
Barrier Beaches Dominate the Atlantic and Gulf Coasts
- Low-lying barrier islands are vulnerable to hurricanes.
- Should be left undeveloped
Is There More Sand on the Beach at the End of the Summer or Winter?
- Gentle summer waves build up the beach.
- Plunging winter storm waves erode the beach.
How Do Dams Affect Beaches?
- Less sediment reaches the beach
- Waves attack cliffs
- Cliffs are eroded
What Are the Problems Presented by Sea Walls?
- Sea walls are built to protect coastal property.
- Waves bouncing back from sea walls erode sand away from beach.
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