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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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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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– 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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• 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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– 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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– 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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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.