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 tectonicsHow 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 tectonicsHow the sea modifies coastlines