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Coastal Systems

Coastlines dynamic, interactive

Change with time

Product of their environment

Inputs Depositional processes

Outputs Erosional processes

Why did/do we live on the coast? Edge Effect ?

Forcing Functions

Deposition Erosion +/- Sea level +/- Energy/Reworking = Coastal geomorphology

Coastal Systems

1. Sea level Global, long-term driver

Eustatic sea level:

Amount of water in the basin

Basin volume

Temperature variations

Local or Relative sea level:Tectonic / isostatic adjustments

Wind, storm surges, currents

1. Eustatic Sea Level

20 feet

High stand

Current

Low Stand

410 feet

Coasts are not in equilibrium,

They are constantlychanging!

2 million years 20,000 years

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Low Stand High Stand

Coasts are not in equilibrium - What is Beachfront Property? Chandeleur Islands

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Dauphin Island Alabama Barrier Islands

USGS

Mainland Mississippi

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LIDAR Images of

Dauphin Island, AL

Photos from USGS

2. Erosional vs Depositional Coastlines

A. Erosional Coasts

Dominant processes remove material

Erosion > Deposition Straight shores, Cliffs, Caves, Platforms

B. Depositional CoastsDominant processes add material

Deposition > Erosion

Beaches, Deltas

2A. Features of an erosional coastline Sea stacks off the coast of Australia

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A blowhole off the coast of Australia

www-class.unl.edu/geol101i/14_coasts.htm

Wave energy convergeson headlandsAnd diverges away from adjoining bays

Shore erosion by region

Deposition exceeds Erosion

Requires constant supply of material

Ex: Beaches and Deltas

2B. Features of a depositional coastline

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Loose particles

Composition

Source

Out to 10 meters water depth

30% of the US shoreline

Beach material characteristics

Features

Dunes

Backshore

Berms

Foreshore

Longshore troughLongshore bar

Beach Processes and Features

Drivers

slope, source material

Wave/wind conditions

Summer beach lower energy deposits sand Winter beach higher energy erodes sand

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Differences in summer and winter

beaches

www.brookdale.cc.nj.us/.../beaches/profile.html

Longshore Drift

Wave approach

Rip Currents

Other Beach Processes and Features

Longshore Drift and Wave

Approach

www-class.unl.edu/geol101i/14_coasts.htm

Rip Currents

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Large-scale features and coastline reworking on a

depositional coast

Three external Forcing Functions shape a delta

River influence

Wave influence

Tide influence

The balance of all three factors determine

the final shape of the delta

Deltas

Formation requires

low slope shelf,

high river influence,low tidal influence,

low wave influence

None on US east coast

None on west NA and

SA coasts

The Mississippi River Delta The Mississippi River Delta is wave dominatedSwitching delta lobes built the coast

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Courses of theCourses of theCourses of theCourses of theMississippi RiverMississippi RiverMississippi RiverMississippi RiverCourses of theCourses of theCourses of theCourses of the

Mississippi RiverMississippi RiverMississippi RiverMississippi River

AlexandriaAlexandria

LafayetteLafayette

BatonRougeBatonRouge

New OrleansNew Orleans

Lake

Charles

Lake

Charles

Cocodrie 2600 B.C. - 1600 B.C.Cocodrie 2600 B.C. - 1600 B.C.

Teche 1900 B.C. - 700 B.C.Teche 1900 B.C. - 700 B.C.

St. Bernard 800 B.C. - 300 B.C.St. Bernard 800 B.C. - 300 B.C.

Lafourche 65 A.D. - 1300 A.D.Lafourche 65 A.D. - 1300 A.D.

Modern 900 A.D. - PRESENTModern 900 A.D. - PRESENT

Ancient & ModernAncient & ModernAncient & ModernAncient & Modern Resulting Ecosystem MosaicResponse to local conditions

Glacial MorainesAre also built out from the land

Formation

Examples

Coasts formed from Biological Activity: Coral Reefs

Fringing Reefs

forms around island in the tropics

Barrier Reef

Separated from land around islands or in lines along shores

The Great Barrier Reef - a conglomerate of reefs,

the largest structure made by living organisms

Atolls

Ring shaped coral reefs with no land

Final phase of tectonic plates moving over a hot spot

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Moora Fringing Reef

The Great Barrier Reef

encarta.msn.com

Kure Atoll

www.oceandots.com/pacific/nwhi/kure.htm

Coasts formed from Biological Activity:

Mangrove Coastlines

Response to local conditions

Trap sediments and provide habitat

Body of water surrounded partially by

land where fresh and ocean water mix

Classification of Estuaries:

Drowned River Mouth

Fjords

Bar-Built

Tectonic

Reverse

Estuaries

River under rising sea level

Drowned River Mouth

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Chesapeake Bay

Glacially eroded

Deep with sill at mouth

Fjord

Fjords

Former low stand of sea level

Low angle coastlines

North Carolina

Florida

Gulf Coast

Bar-Built

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Outer Banks, NC

www.cetialpha.com/photos/earth_fm_space/

Active plate Margins

Coastline falls off?

Tectonic

San Francisco Bay, CA Reverse Estuary

Minimal freshwater input

High evaporation rates

Higher salinity than ocean

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Characteristics of Estuaries

Amount of mixing between fresh water

and salt water determined by:

Shape of the estuary Volume of river flow at the head

Tidal range at the mouth

Estuaries are categorized by their

circulation patterns

Salt Wedge vs. Well Mixed etc.