physical geography lecture 17 - oceans and coastal geomorphology 120716
TRANSCRIPT
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Coastal Geomorphology:The Oceans, Coastal
Processes, and LandformsChapter 13
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Characteristics of Ocean Water:Salinity, Temperature, and
Density
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Warm and Cold Ocean Currents
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The Movements of The Oceans•Tides•Currents•Wave motion
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Tides•A “bulge” in the world’s oceans, caused by the gravitational pull of the moon and sunFg = G m1 m2
d2
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Tides• Tidal range—the
difference between high and low tide
• Affected by the shape of the coastline and seafloor
• Spring tides—highest tides, strong and quick– Occur when sun, moon,
and Earth line up (the sea “springs” up and back)
• Neap tides—lowest tides– Sun and moon at right
angles with respect to Earth
– Neap = A low incline of bend (when graphed)
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Monthly Tidal Cycle
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Extreme High Tides
• The Bay of Fundy• A 50’ (15m) tidal fluctuation is common (x2)•A tidal bore (several in. to several ft. high) rushes miles up the Petitcodiac River in New Bruswick
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Landforms shaped by extreme tides
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Extreme tides: Mont Saint Michel, France
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Low tide High tide
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Currents: Thermohaline Circulation
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Currents: Surface
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Waves and Wave Dynamics
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Waves and Wave Dynamics•Period—The time it takes two successive waves (from crest to crest, or from trough to trough) to pass a given point
•Fetch—The distance over which the wind blows, creating waves
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Waves and Wave Dynamics•Factors affecting open ocean waves:
–Fetch•The greater the distance over which the wind blows, the larger the waves
–Wind strength•The stronger the wind, the larger the waves
–Wind duration•The longer the wind blows, the more waves will be created
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Waves and Wave Dynamics
Wave base
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Wave Base = 1/2 wave length
Wave base
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Waves of Oscillation vs. Translation
Waves of oscillation
Waves of translation
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Waves of Oscillation (Transition) and Waves of Translation
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Wave Break
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Wave Refraction,Longshore Current and Beach Drift
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Erosional Environments•If there is not enough sediment replacing what’s being lost through wave erosion/longshore current, erosion will occur, creating a rocky coastline–Dammed or channelized streams
•sediment can’t get to the beach•Erosive environments create distinctive landforms–rocky headlands and pocket beaches, sea arches and sea stacks, wave-cut cliffs, wave-cut platforms, wave-built terraces, etc.
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Wave Energy is Concentrated at Headlands and Dissipated in Bays
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Wave Motion and Wave Refraction
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Wave Motion and Wave Refraction
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Laguna Beach, CAHeadlands
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Headland Erosionand the Formation of Sea Arches
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Stacks and CliffsVictoria, Australia
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The Holderness Coast is one of Europe's fastest eroding coastlines. The average annual rate of erosion is around 2 metres per year. The main reason for this is because the bedrock is made up of till. This material was deposited by glaciers over 18,000 years ago.
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Erosional Environments:Shoreline Retreat
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Depositional Environments:Welcome to the Dunes…Now Get Off!
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The Structure of a Beach
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Common Depositional Landforms
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Barrier Island Structure
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Lagoons, Marshlands, and the Formation of New Coastlines
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Submergent Coastlines
Ria CoastFjord Coast
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Emergent Coastlines
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Formation of a Wave-cut Platformand Uplifted Marine Terraces
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Formation of a Wave-cut Platformand Uplifted Marine Terraces
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Formation of a Wave-cut Platformand Uplifted Marine Terraces
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Barrier Island Coast
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Padre Island, Texas
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Coral Coast
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Formation of an Atoll
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Formation of an Atoll
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Formation of an Atoll
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Coral Coast
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“Any serious researcher would be hard-pressed to find a marina, a sea wall, or any other human structure along the shoreline that does not pose some long-term deleterious effects to both the natural and cultural environments it attempts to protect.”
--Physical Geography: Earth’s Interconnected Systems
Angela Orr, 2007
Coastal Stabilization and Human Impact
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Coastal Stabilization and Human Impact•Damming and channelizing streams
–Causes a loss of sediment where streams empty into the sea. Without sediment, the beach will erode away.
•Groynes (groins)•Seawalls•Breakwaters and jetties
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Coastal Stabilization Structures
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Groynes (groins)
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Groynes (groins)
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Coastal Stabilization Structures:Breakwater
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Marina del Rey