Coast and Shore  

Coast and Shore
Coasts are temporary structures, often subjects to rapid change. The shape of a coast is a product of many processes: uplift and subsidence, the wearing down of land by erosion, and the redistribution of mineral by sediment transport and deposition.

Classifying coasts
Active coasts
Passive coasts
Eustatic change

The location of a coast depends primarily on global tectonic activity and the volume of water in the ocean.


Change in sea level greatly influences coastal processes. For most of Earth’s recent history, sea level has been lower than we find today.

Erosional coasts
Depositional coasts

Erosional coasts are new coasts in which the dominant processes are those removing coastal material. Depositional coasts are those coasts that are steady or growing because of their rate of sediment accumulation or the action of living organisms.


EROSIONAL COASTS
Features of an erosional coast at low tide:
-wave-cut platform
-notch eroded by waves
-original land surface
-sea cliff

Features of Erosional Coasts

-exposed beach
-sea arch
- sea cliffs
-sea cave
-sea stack
-headland
-blowhole


High-energy coasts
Low-energy coasts

Shore Straightening
Land Erosion Coasts
- drowned river mouth (the Hudson River)
- fjords are often formed by tectonic forces and later modified by glaciers eroding valleys (British Columbia, Greenland, Alaska, Norway, New Zealand).
- Volcanic coasts.


DEPOSITIONAL COASTS
Beaches
The Composition and slope of beaches
-the swash
-the backwash
-the berm

A typical beach profile.
-high tide-low tide (dotted line)
-longshore bars
-longshore trough
-berm crest
-beach scarp
Dunes

Water-land:
-offshore
-nearshore (through breakers)
-foreshore
Backshore

Longshore Transport
A seasonal change , sand moves on and off Boomer Beach near La Jolla, CA. Gentle summer waves move sand onshore, but large winter waves remove the sand to offshore bars, exposing the basement rock.

Longshore drift
Longshore current – moves sediment along the shoreline between the sure zone and the upper limit of wave action.

-Surf zone
-upper limit of wave action
-path followed by sand grains
-direction of wave approach

Depositional coasts often support beaches, accumulations of loose particles. Beaches change shape and volume as a function of wave energy and the balance of sediment input and removal.

Coastal Cells
Imput and sand outflow
Coastal cells in Southern California

Sand Spits and Bay Mouth Bars
Tombolo
Barrier island inlet
Lagoon
Sea islands

Depositional coastspecially along subsiding continental margins, often exhibit characteristics large-scale features.

Deltas
-river dominated deltas
Tide-dominated deltas
-wave-dominated deltas

Deltas form on broad continental shelves where rivers deposit sediments, tidal range is low, and wave and current action are generally mild.


COASTS FORMED BY BIOLOGICAL ACTIVITY

The Florida Keys – a coral reef in the US. A mangrove coast in Florida. Mangrove trees sediments , building and stabilizing the coast.

Coasts can be extensively modified by the action of living organisms.


ESTUARIES.

Classification of Estuaries
-Drovned river mouths
-Fjords
Bar-built
-Tectonic

Characteristics of Estuaries
-Salt wedge estuaries
-Well-mixed estuaries
-Partially mixed
- Fjord

Estuaries can form at river mouths where fresh water mixes with seawater. Estuaries are amoung the most complex and biologically productive coasts.

The value of Estuaries. Chesapeake Bay

CHARACTERISTICS OF U.S. COASTS

The Pacific Coast – the active margin.

Most of sediments on the Pacific coast originated from erosion of relatively young granitic or volcanic rocks of nearby mountains.
Wave-cut terraces on San Clemente Island

The Atlantic Coast – the passive margin. Glaciers. The sea level was lower.

The Gulf Coast experiences a smaller tidal range and – hurricanes expected. Reduced longshore drift and absence of interrupting submarine canyons and the great volume of accumulated sediments.

HUMAN INTERFERENCE IN COASTAL PROCESSES
-the breakwater in Santa Monica did beach bigger
-groins
-seawall
-inporting sand

Human interference in coastal processes rarely increases the long-term stability of a coast.

Coastal classification
Primary coast: Unmodified--morphology controlled by recent geologic history

Land erosion coasts
Ria coast drown river valleys: indented--shape controlled by drainage basin pattern
Drowned glaciated coast (e.g. Deep coastal valleys--fiords)
Examples:

SØNDRE STRØMFJORD, Western Greenland
Southwest Ireland
West Faukland Island
Southwestern Sweden
TRÖLLASKAGI, Iceland

Drowned karst topography
Subaerial deposition coasts
River deposition coasts
Deltaic coasts (single delta complex)
Compound delta coasts
Compound alluvial fan coasts
Glacial deposition coasts
Partially submerged moraines
Partially submerged drumlins (Boston Harbor drumlins)
Partially submerged drift features
Wind deposition coasts
Landslide coast
volcanic coasts
shaped by diastrophic movements (faulted coasts)
Ice coasts



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Secondary Coasts (modified by coastal processes)
Wave erosion coasts
Wave straightened cliffs
Differentially eroded coasts
Marine deposition coasts
Barrier beach
Barrier island
Barrier spit
Bay barrier
Coasts built by organisms
coral reef coasts (fringing reef, barrier reef, atoll, keys, etc.)
More about reefs:

Coral reefs: Florida Keys National Marine Santuary
Coral reefs from online books: Essentials of Oceanography and Marine Ecology
Reefs of the Gulf of Mexico
Coral reefs in Belize
The Great Barrier Reef, Australia (National Geographic)
Midway Atoll
Serpulid reef coasts
Oyster reef coasts
Mangrove coast
Mangroves-Florida''s Coastal Trees (University of Florida)
Collection of Mangrove resources (Florida Plants Online)
marsh grass coast
Pros and cons of Shepard''s classsification: His classification is thorough, but cumbersome. Also many coasts may fall under more than one classif
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