Wave Erosion and Marine Geology
How waves behaveHow the sea modifies coastlines
Waves
Essential Points1. Waves are created by the wind2. Water in waves oscillates but does not
move with the wave3. What happens when waves hit the shore4. Storm surges can be catastrophic
How Waves Behave
Wave Fetch
Wave Fetch
The Highest Recorded Ocean Wave
1. Waves are created by the wind
Global Wave Heights
1. Waves are created by the wind
Freak Waves • Addition of waves of different frequencies
• Theoretically could reach 200 feet in Gulf of Alaska
• One nearly sank the Queen Mary in WWII, with 15,000 troops aboard.
1. Waves are created by the wind
Wave Motions
• Particles in a wave travel circular paths• The water in a deep-water wave does not
move forward• Below wave base, wave effects are negligible
2. Water in a wave oscillates but does not move with the wave
Wave Motions
2. Water in a wave oscillates but does not move with the wave
When Waves Meet the Shore
When the bottom interferes with wave motion, the wave steepens and the top overtakes the bottom.
3. What happens when waves hit the shore
Wave Refraction
• Waves change path when they reach shallow water• Wave energy is concentrated on headlands and
spread out in bays
3. What happens when waves hit the shore
Wave Refraction off Cape Cod
3. What happens when waves hit the shore
Rips
• When waves break parallel to a beach, rips occur
3. What happens when waves hit the shore
Rips, Lake Superior
Oblique Rips
3. What happens when waves hit the shore
Storm Waves: Galveston, Texas, September 8, 1900:
• 6000-8000 dead• 3600 houses destroyed
4. Storm surges can be catastrophic
Raising Galveston – 6 in. to 17 ft.
“A rickety maze such as Dr. Seuss might have drawn”
The Lift in Progress
Pumping in the Sand
4. Storm surges can be catastrophic
The Galveston Seawall
4. Storm surges can be catastrophic
Essential Points1. Waves are created by the wind2. Water in waves oscillates but does not
move with the wave3. What happens when waves hit the shore4. Storm surges can be catastrophic
How Waves Behave
How the sea modifies coastlines
Essential Points1. Wave Action erodes or deposits material
along coastlines2. Types of coastline3. Deltas are governed by deposition, waves,
and tides4. Reefs are a special type of coastline in
tropical regions5. Global sea level is affected by ice ages and
plate tectonics
How the sea modifies coastlines
In the long run, nothing is as futile as trying to resist shoreline
change.
Change can be resisted for a while, but when the water wants
something badly enough, it will come in and take it.
1. Wave Action erodes or deposits material along coastlines
Property Values and Shoreline Erosion
• If more than half the original lot is left, it’s Location, Location, Location
• After that, it becomes obvious there soon won’t be any location left
1. Wave Action erodes or deposits material along coastlines
Marine Erosion
• Chemical Attack • Abrasion • Wave Impact • Compressed Air • Backwash
1. Wave Action erodes or deposits material along coastlines
Water Velocity and Erosion
1. Wave Action erodes or deposits material along coastlines
Longshore and Beach
Drift
• Most Beach Sand Is Created by Weathering and Carried to Coasts by Rivers
• Beach Sand Moves along the Coast by Longshore and Beach Drift
1. Wave Action erodes or deposits material along coastlines
Beach Drift, New Jersey
Types of CoastDegree of Modification• Primary - Not Modified Much by Wave Action• Secondary - Highly Modified by Wave Action History• Emergent - Land Rises or Water Level Falls• Submergent - Land Sinks or Water Level Rises Dominant Process• Erosional• Depositional
2. Types of coastline
Effects of the Pleistocene
• Sea level has risen at least 100 meters in the last 18,000 years
• Most coastlines globally are submergent• Primary coastlines are very common
2. Types of coastline
Secondary Coasts Are Modified by Marine Erosion or Deposition
Secondary CoastsErosion• Stack • Terraces • Tombolo • Erosion rate becomes very
slow – wave energy dissipated
crossing the wave-cut terrace. – Cliffs become higher, meaning
more material to move.
Deposition• Spit • Lagoon • Baymouth Bar • Barrier Bar
2. Types of coastline
Primary Coastlines Are Very Common
• Drowned River Valleys (Estuaries)
• Drowned Glacial Valleys (Fiords)
2. Types of coastline
Estuaries, Chesapeake Bay
Tidal Marshes,
Chesapeake Bay
2. Types of coastline
Fiord Coast, Labrador
Other Ways Primary Coasts Can Form
• Deltas • Volcanic Activity • Uplift
2. Types of coastline
Primary and Secondary Coastlines
2. Types of coastline
Baymouth Bar, Michigan
Wave-Cut Platform, California
Footer
Coastal Terraces, California
Sea Stacks, Washington
Former Stack, Michigan
Sea Caves, Apostle Islands
Wave-Cut Arch, Lake Superior
Delta Coasts
• Deposition-Dominated• Wave Dominated• Tide-Dominated
3. Deltas are governed by deposition, waves, and tides
The Mississippi – A Deposition-Dominated Delta
3. Deltas are governed by deposition, waves, and tides
Yukon and Nile Deltas – Balance of Deposition and Wave Action
3. Deltas are governed by deposition, waves, and tides
Sao Francisco, Brazil – A Wave-Dominated Delta
Ganges, Bangladesh – A Tide-Dominated Delta
Reefs Are a Major Type of Coast in Tropical Areas
4. Reefs are a special type of coastline in tropical regions
Fringing Reef, Tahiti
Tarawa – A Typical Atoll
4. Reefs are a special type of coastline in tropical regions
Reefs Also Form along the Edges of Large Islands and Continents
These Are Barrier Reefs • Australia • Yucatan • Belize • West Florida and the Keys
4. Reefs are a special type of coastline in tropical regions
Sea Level and Tectonic Activity
5. Global sea level is affected by ice ages and plate tectonics
Depth of Ocean Crust
5. Global sea level is affected by ice ages and plate tectonics
Sea-Floor Spreading and Sea Level
5. Global sea level is affected by ice ages and plate tectonics
Sea Level and Tectonic Activity
5. Global sea level is affected by ice ages and plate tectonics
Essential Points1. Wave Action erodes or deposits material
along coastlines2. Types of coastline3. Deltas are governed by deposition, waves,
and tides4. Reefs are a special type of coastline in
tropical regions5. Global sea level is affected by ice ages and
plate tectonics
How the sea modifies coastlines