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““The sea heaves up, hangs loaded o'er the The sea heaves up, hangs loaded o'er the land, Breaks there, and buries its tumultuous land, Breaks there, and buries its tumultuous

strength.strength. ” ”

— — Robert Browning Hamilton Robert Browning Hamilton (Brainyquote.com)(Brainyquote.com)

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The Impact of Waves and Currents on the Landscape

Coastal Processes Coastal Landforms Summary

Coastal Processes and Terrain

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The Impact of Waves and Currents on the Landscape• Coastal Processes

– Erosion – Waves, mainly– Deposition – Currents, mainly

• Rocky cliffs and headlands– Main erosional features

• Beaches and sandbars– Main depositional features

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Coastal Processes• Erosion and Deposition

– Involve the transfer of energy from the atmosphere to the hydrosphere (ocean) and then to the lithosphere (land).

Kinetic energy transfer

Wind Deposition

Erosion

Wind

Coast

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• Geomorphic agents – Waves

• Wind-generated waves• Other sources of waves

– Other agents• Longshore currents• Tides and tidal currents• Volcanic eruptions and earthquakes• Tidal (storm) surges• Long-term (tectonic and climatic) effects on sea level

change• Reef-building corals• Sea ice• Glaciers

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WavesAnimation • Definition – A disturbance in water caused by energy

passing through it.• Wave terms: wavelength, wave crest and trough,

swash

1. Wave Motion and Wave Refraction2. Tsunami

– Fig. 20-2

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• Waves of Oscillation and Translation– Wave of Oscillation – energy and mass move

differently

H2O particles – orbital paths

Energy

– Fig. 20-2

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– Wave of Translation – energy and mass move in the same direction (horizontally)

– Fig. 20-3

shore

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– Wave Refraction

– Fig. 20-5

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Side view of headland

• Headland erosion (idealized)

SA

Wave Refraction(blue lines)

Headland

Eroding Sea cave

X Sea arch

Sea stack

SS

H

SC

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– Fig. 20-6. Headland erosion in Australia along the southern coast of the state of Victoria.

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– Wave Erosion• Hydraulic pounding• Chemical action• Sea cliff erosion

– Fig. 20-7

NotchWave-cut platform

Cliff face

Sea Level

Former shore

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– Tsunami (Seismic Sea Waves)• Rapid, pronounced vertical displacement• Main causes

– Earthquake (submarine)

– Landslide (submarine)

– Volcanic island eruption

Sea level

Seafloor

Fault

Sea levelSea level

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– Fig. 20-8. Formation of a Tsunami.

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• TidesAnimation (Tides)– Significant erosion agents in narrow bays, margins

of shallow seas, and straits.

• Fig. 20-9. Bay of Fundy has the highest tidal range in the world. Tidal action created these pedestal rocks on the edge of the bay.

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• Changes in Sea Level and Lake Level– Causes

• Tectonic uplift or sinking of landmass• Eustatic – increase or decrease in the volume of water in

the oceans (Pleistocene glaciations).

– Fig. 20-10. Northern California coast is experiencing tectonic uplift.

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– Global Warming and Sea-Level Change• Causes

– Thermal expansion

– Glacial melting

• Consequences by 2100– Sea Level rise – Up to 0.5 m (20”) rise

– Retreat of shorelines – Up to 30 m (ca. 100 ft.) in some areas.

• Ice Push– Annual freezing of sea ice causes near-shore ice

to push against the land, causing minor erosion– Arctic and Antarctic regions only

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• Organic Substances– Calcium carbonate

secretions– Reef-building coral

polyps

• Stream Outflow– Source of sediment

for beaches– Fig 20-11. Sediment plume of

the Betsiboka River, Madagascar.

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• Currents and Coastal Sediment Transport– Longshore Currents

• Wave refraction

- Energy bends upon entering shallow water

shore

-2 m

-6m

-1m

DepthLongshore current

Undertow diverted by incoming waves

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– Beach Drifting• Particle-by-particle transport of beach material

Wave refraction (bending)

Beach

W1 W2 W4W3

backwash

= sand particle

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– Fig. 20-13. Waves approaching the shore obliquely causes longshore currents and beach drifting.

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• Coastal Deposition– Sediment budget of a

shore• Inputs from longshore

current supply and wave action

• Outputs from storm wave action, mainly.

– Large beaches and sand dunes

• Inputs exceed outputs.

• Fig. 20-14. One of the largest coastal dune complexes is on the Oregon coast.

Fig. 20-14

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Coastal Landforms• Depositional Landforms

Animation (Coastal Stabilization Structures)

– Beaches• Most widespread marine dispositional feature on land

– Mostly sand deposits

• Extent– Inland margin (storm wave deposits)

– Seaward margin (neap tide line)

Sea Level?

?Extent

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• Components of the beach environment

– Fig. 20-15

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– Spit and related features• Spit: Linear strand of marine sediments attached to shore• Formation usually involves longshore current transport• Related features

– Fig. 20-16. Types of spits and the longshore current.

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• Idealized drawings of formation of spit and related features

(3) Baymouth bar(2) Hook

Land

Ocean

Bay

(1) Simple spit

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• Tombolo formation

Land Ocean

Small island, sea stack

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• Photographs of spits and related features

– Fig. 20-17. Spit at Cape Henlopen, Delaware

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– Fig. 20-18. Tombolo and Mont Saint Michel on the northwest coast of France.

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– Barrier Islands• Coastal islands, parallel to the mainland shore• Complex origins

– Pleistocene sediments washed toward mainland

– Longshore transport and spit segmentation

Land Ocean

Bay

Barrier Is

land

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• Lagoon formation– Landward side of barrier island, protected from large waves

– Low energy environment, fine mud deposits (tidal flats)

– Fig. 20-19

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– Human Alteration of Coastal Sediment Budgets• Beach starvation (unintentionally shrinking beaches)

– Dam construction on rivers reduces sediment discharge into oceans, starving nearby beaches of sand

– Old debris dam in Santa Ynez Mountains, near Santa Barbara, CA (Richard A. Crooker photo)

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• Beach nourishment (re-building beaches)– Adding sand to beaches by dredging and pumping sand

from off-shore

– A slurry of sand and water is pumped on shore and the sand is spread onto the beach of Rehoboth Beach, DE (Richard A. Crooker photos) (overlay, dissolve)

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• Beach preservation (maintaining beaches)– Build structures that modify longshore transport and wave

action in order to keep sand on beaches

– Jetty

– Groin

– Fig. 20-22

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• Shorelines of Submergence– Ria Shorelines

• Hilly or mountainous areas– flooded valleys become estuaries

- Fig. 20-23. Chesapeake Bay.

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– Fjorded Coasts• Fjord – glacial trough that is inundated by the sea

– Fig. 20-24

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– Wave-cut Cliffs and Platforms– Marine Terraces

- Fig. 20-27. Near Fort Ross, CA

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• Coral Coasts– Coral Polyps

• Reef-building varieties, warm tropical waters

– Fig. 20-28

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– Shallow-water Platforms• Australia’s Great Barrier Reef

– Fig. 20-30

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– Sinking Islands• Three types of reefs

Sea Level

Fringing

Sea Level Barrier

Sea Level Atoll

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– Fig. 20-31

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– Fig. 20-32. Part of the fringing reef on the island of Moorea, French Polynesia.

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Summary• The principal forces shaping coastlines are

changes in sea level, tides, waves, currents, stream outflow, ice push, and organic secretions.

• Waves cause erosion as they constantly crash onto the shore.

• Waves and longshore currents transport sediments along a coast.

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• Landforms along coastlines include beaches, wave-cut benches, wave-built terraces, and barrier islands and their lagoons, spits, fjords, and coral reefs.