Wave Erosion and Marine Geology

Take-Away Points1. Waves are created by the wind

2. Water in a wave oscillates but does not move with the wave

3. What happens when waves hit the shore

4. Storm surges can be catastrophic

5. How coastlines evolve

6. Deltas are influenced by deposition, tides, and wave action

7. Reefs are important coastlines in tropical regions

8. Submarine landslides

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

1. Waves are created by the wind

Wave Motions


The Highest Recorded Ocean Wave


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.

When Waves Meet the Shore

When the bottom interferes with wave motion, the wave steepens and the top overtakes the bottom.


Wave Refraction

• Waves change path when they reach shallow water

• Wave energy is concentrated on headlands and spread out in bays


Rips

• When waves break parallel to a beach, rips occur


Storm Waves: Galveston, Texas, September 8, 1900:

• 6000-8000 dead

• 3600 houses destroyed


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


The Galveston Seawall


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.

5. How Coastlines Evolve

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


Marine Erosion

• Chemical Attack

• Abrasion

• Wave Impact

• Compressed Air

• Backwash


Longshore and Beach

Drift

• Most Beach Sand Is Created by Weathering and Carried to Coasts by Rivers

• Beach Sand Moves along the Coast by Longshoreand Beach Drift


Longshore Drift


Types of Coast

Degree 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


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


Secondary Coasts Are Modified by Marine Erosion or Deposition


Secondary Coasts

Erosion

• Stack

• Terraces

• 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


Primary Coastlines Are Very Common

• Drowned River Valleys (Estuaries)

• Drowned Glacial Valleys (Fiords)


Other Ways Primary Coasts Can Form

• Deltas

• Volcanic Activity

• Uplift


Primary and Secondary Coastlines


Delta Coasts

• Deposition-Dominated

• Wave Dominated

• Tide-Dominated


The Mississippi – A Deposition-Dominated Delta


Yukon and Nile Deltas – Balance of Deposition and Wave Action


Sao Francisco, Brazil – A Wave-Dominated Delta

Ganges, Bangladesh – A Tide-Dominated Delta

Reefs Are a Major Type of Coast in Tropical Areas


Tarawa – A Typical Atoll


Reefs Also Form along the Edges of Large Islands and Continents

These Are Barrier Reefs

• Australia

• Yucatan

• Belize

• West Florida


Turbidity Flows – Grand Banks, 1929

8. Submarine Landslides

Take-Away Points1. Waves are created by the wind




5. How coastlines evolve



8. Submarine landslides

Wave Erosion and Marine Geology - Maejo University

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