physical geography lecture 17 - oceans and coastal geomorphology 120716
TRANSCRIPT
Coastal Geomorphology:The Oceans, Coastal
Processes, and LandformsChapter 13
Characteristics of Ocean Water:Salinity, Temperature, and
Density
Warm and Cold Ocean Currents
The Movements of The Oceans•Tides•Currents•Wave motion
Tides•A “bulge” in the world’s oceans, caused by the gravitational pull of the moon and sunFg = G m1 m2
d2
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)
Monthly Tidal Cycle
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
Landforms shaped by extreme tides
Extreme tides: Mont Saint Michel, France
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Low tide High tide
Currents: Thermohaline Circulation
Currents: Surface
Waves and Wave Dynamics
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
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
Waves and Wave Dynamics
Wave base
Wave Base = 1/2 wave length
Wave base
Waves of Oscillation vs. Translation
Waves of oscillation
Waves of translation
Waves of Oscillation (Transition) and Waves of Translation
Wave Break
Wave Refraction,Longshore Current and Beach Drift
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.
Wave Energy is Concentrated at Headlands and Dissipated in Bays
Wave Motion and Wave Refraction
Wave Motion and Wave Refraction
Laguna Beach, CAHeadlands
Headland Erosionand the Formation of Sea Arches
Stacks and CliffsVictoria, Australia
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.
Erosional Environments:Shoreline Retreat
Depositional Environments:Welcome to the Dunes…Now Get Off!
The Structure of a Beach
Common Depositional Landforms
Barrier Island Structure
Lagoons, Marshlands, and the Formation of New Coastlines
Submergent Coastlines
Ria CoastFjord Coast
Emergent Coastlines
Formation of a Wave-cut Platformand Uplifted Marine Terraces
Formation of a Wave-cut Platformand Uplifted Marine Terraces
Formation of a Wave-cut Platformand Uplifted Marine Terraces
Barrier Island Coast
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Padre Island, Texas
Coral Coast
Formation of an Atoll
Formation of an Atoll
Formation of an Atoll
Coral Coast
“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
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
Groynes (groins)
Groynes (groins)
Coastal Stabilization Structures:Breakwater
Marina del Rey