Coastal ClassificationCoastal Classification

Most group coastal areas into classes that have similar features because of having developed in similar geological and environmental

settings.

By its very nature, the coast is an incredibly complex and diverse environment, one that may defy organization into neat compartments.

Nevertheless, the quest for understanding how shorelines form and how human activities affect these processes has led the creation of

classification schemes.

This is called the “geologic framework” andIt is the motivating ideal behind the USGS Marine and

Coastal Geology Program

Headlands, Embayments,Tombolos, Channel Mouths, Beaches, Tidal Flats, Estuaries

Shepard’s 1973 ClassificationShepard’s 1973 Classification

Divides the world’s coasts into primary coasts – formed mostly by non-marine agents - and

secondary coasts - shaped primarily by marine processes.

Further subdivisions occur according to which specific agent, terrestrial or marine, had the greatest influence

on coastal development.

Although gradational shore types exist, which are difficult to classify, most coasts show only one dominant influence.

Primary coast – nonmarine agent

Secondary coast – marine agent

Primary CoastsPrimary CoastsLand Erosion CoastsLand Erosion Coasts

Land erosion coasts Shaped by subaerial erosion and partly drowned by postglacial rise of sea level.

Ria Coasts (Chesapeake Bay)

Dendritic (flooded drainage in horizontal beds)

Trellis (glacial erosion, fjords, Gulf St. Lawrence)Drowned Karst Topography (northwest Florida)

Land Erosion Coast – Ria Coast

Florida, flooded karsterosion due to dissolutionflooded by sea-level rise

Glacier Bay, flooded fjorderosion by glaciationflooded by sea-level rise

Primary CoastsPrimary CoastsSubaerial Deposition CoastsSubaerial Deposition Coasts

River deposition coasts Deltaic coasts (Mississippi Delta) Compound delta coasts (north slope - Pt. Barrow

to MacKenzie River) Compound alluvial fan (straightened by erosion) Glacial deposition coasts (Cape Cod) Wind deposition coasts (Sleeping Bear St. Park) Landslide coasts (Martinique)

Cape Cod regionglacial deposition

Mississippi deltasubaerial deposition

Sleeping Bear, Michigansubaerial deposition, dune

Primary CoastsPrimary CoastsVolcanic CoastsVolcanic Coasts

Lava Flow Coasts (Big Island)Tephra CoastsVolcanic Collapse Coasts (Hanauma Bay)

Primary Volcanic Coast

Collapsed Volcanic Coast

Pyroclastic surgeMontserrat

Primary CoastsPrimary CoastsShaped by Diastrophic MovementsShaped by Diastrophic Movements

Fault CoastsFold CoastsSedimentary Extrusions (salt domes, mud

lumps, Red Sea)

Diastrophism – movement of the crust

Primary CoastsPrimary CoastsIce CoastsIce Coasts

Glacial Ice and Sea Ice

Primary Ice CoastCollapsing Larson B ice shelf

Wave-straightened cliffsMade irregular by wave erosion

Secondary CoastsSecondary CoastsWave Erosion CoastsWave Erosion Coasts

Wave straightened cliffs

Maui lava flows – irregular erosion resistance

Secondary CoastsSecondary CoastsMarine Deposition CoastsMarine Deposition Coasts

Barrier CoastsCuspate forelandsBeach PlainsMud Flats/Salt Marshes

Primary Marine DepositionCuspate Foreland Coast

Holocene beachStrand plain

Coral Reef CoastSerpulid Reef CoastOyster Reef CoastMangrove CoastMarsh Grass Coast

Secondary CoastsSecondary CoastsCoasts Built by OrganismsCoasts Built by Organisms

Submergent Coasts•Relative sea level is rising•Estuaries formed in drowned river mouths

Emergent Coasts•Relative sea level is falling•Tectonics or isostasy responsible for most types

Depositional Coasts•Wide sandy beaches, stream deltas, overabundance of sediment

Erosional Coasts•Irregular coastline, narrow beaches, eroding headlands

Convergent Coasts•Sea Cliffs common, narrow continental shelf, relatively straight and mountainous

Other Classification Schemes

Passive Margin Coasts•Broad continental shelf•Plate trailing edge

Submergent Coast

Emergent Coast

Depositional Coast – Mississippi River Delta

Erosional Coast – “12 Apostles”

Convergent Coast –

Trailing Coast –

Delta Classification-tide dominated-river dominated-wave dominated

Shorelines straighten with time