coasts - key ideas › ~mitterer › oceanography › ...1 1 coasts - key ideas lcoasts are...

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Coasts - Key Ideas

l Coasts are temporary structures, often subject torapid change.

l The location of a coast depends on tectonic activityand the level of water in the ocean.

l Coasts are classified as primary or secondary.

l Human interference in coastal processes rarelyincreases the long term stability of a coast.

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Classifying Coasts

Coasts can be classified by a method that takesinto account tectonic position and sea level.

Primary coasts are young coasts dominated byterrestrial influences.

Secondary coasts are older coasts that havebeen changed by marine influence.

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Types of Primary Coasts

• Drowned rivers

• Coasts built out by land processes (e.g., rivers, glaciers)

• Volcanic coasts

• Coasts shaped by tectonic processes

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Primary Coasts

Many of the islands of Martha’s Vineyard and Nantucket areexamples of a primary coast.

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• Waves and currents

• Stream erosion

• Wind abrasion

• Freeze/thaw cycles

• Slumping

Processes Shaping Coasts

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Secondary Coasts

Waves are one of the forces that shape secondary coasts.

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Alternative Classificationof Coasts

l Erosional Coastsl Features are: headlands, cliffs, stacks,

arches, wave-cut platform

l Depositional Coastsl Features are: barrier islands, deltas, glacial

deposits

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Other Types of Coasts

l Drowned Coastsl Estuaries, fiords

l Emergent or Uplifted Coastsl Uplifted marine terraces

l Coasts affected by organismsl Reefs, mangroves

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Beaches

A beach is a zone of loose particles that covers a shore.

Note that largerparticles are associatedwith more sloped beach.

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Features of Beaches

• berm• berm crest• backshore• foreshore• beach scarp• longshore trough• longshore bars

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Beaches

The features of a beach.

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Wave Refraction and Longshore Current

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Longshore Drift

l Features formed by longshore driftl Spit, baymouth bar, tombolo

l Human interference with longshore driftl Jetties, groins, breakwaters

l Sources of sand

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Large Scale Features ofSecondary Coasts

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Origin of Barrier Islands

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Sections of coast in which sand input and sand outputare balanced are referred to as coastal cells.

Coastal Cells

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Coral Reefs are the most dramatic of the coasts formed by biological activity.

Coasts Formed by BiologicalActivity

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Coral Reef Classifications

Fringing Reefs cling to the margin of land.

Barrier Reefs are separated from land by alagoon.

Atolls are ring-shaped islands of coral reefenclosing lagoons.

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Storm Surges

A storm surge is an abrupt bulge of water driven on shoreby a tropical cyclone or a frontal storm.

Storm surges are short-lived.

Storm surges consist of only a crest, so they cannot beassigned a period or wavelength, and cannot be called awave.

Storm surges are sometimes called storm tides.

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Human Interference on CoastalProcesses

• Groins

• Seawalls

• Importing sand

These methods are largely ineffective in solving beacherosion.

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Coasts

A map showing shore erosion by region. One example of shore erosion is thelighthouse on Cape Hatteras, which was moved during 1998 and 1999 to protect itfrom destruction. It was threatened by rising sea levels and a changing shoreline.

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The Pacific Coast - An actively rising margin where indications of recenttectonic activity can be observed.

The Atlantic Coast - A passive margin on the trailing position of theNorth American plate.

The Gulf Coast - Smaller wave size and a smaller tidal rangecharacterize the Gulf Coast.

Characteristics of U.S. Coasts

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A few of the many typesof measures taken toslow and prevent beacherosion. Some of thesemethods are actuallycounterproductive.

In many cases thesemethods help serve asa reminder thatshorelines and beachesare constantly changing,and are not underhuman control.

Summary

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Estuaries

An estuary is a body of water in which fresh river water mixeswith ocean water. Estuaries can be classified by their origin.

• Drowned river mouths

• Fjords

• Bar-built

• Tectonic

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39The four types of estuaries.

Estuaries

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Salt-Wedge Estuary(river-dominated)

Examples: Mouths of Mississippi, Hudson and Columbia Rivers

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Well-Mixed Estuary(tide-dominated)

Examples: Shallow estuaries such as Chesapeake and Delaware Bays

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Partially Mixed Estuary

Examples: Puget Sound and San Francisco Bay

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Fjord-Type Estuary

Examples: Glaciated coastal mountains

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Estuarine Water Budget

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Positive Water Balance Estuary

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Negative Water Balance Estuary