physical geography lecture 17 - oceans and coastal geomorphology 120716

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