Shorelines

Beaches and Coasts

• The coastal zone and beaches along the continental margin are among the most dynamic geologic setting on earth

• Human settlements are concentrated along the coast and most of the world’s population lives along the coast

• Human activities along the coast oftentimes accelerate coastal erosion processes

Nearshore Circulation

• Waves• Wave Refraction• Longshore Currents• Rip Currents

Still Water Line

Wave Amplitude

Wave Morphology

Wave Refraction

• As waves approach the shore they will bend or refract because of their interaction with the seafloor

• As the wave enters shallow water it will slow down as a consequence of friction or drag with the seafloor; however the wave portion in deep water still moves relatively faster

• The wave front then turns or refracts

Longshore Drift

• Sediment movement along the coastline is done by longshore currents and is termed longshore drift

Rip Currents

• Rip currents are very strong currents that flow out to sea in the surf zone

THE COASTAL ZONE

subtidalintertidalsupratidal

or Dune

Sources of Sand

Sand, Gravel, Pebble, Cobble

Quartz

Volcanic

Carbonate

Nearshore FeaturesDepositional Coasts

– Dunes– Beach Face, Berms– Beach sediment– Barrier Islands– Spits, baymouth bars, tombolos

Erosional Coasts– Headlands– Sea Cliffs, Sea Stacks, Sea Arches and Sea

Caves– Wave-Cut marine Terraces

Coastal Development

• Coastal development is increasingly important to the economic development of many countries

• However coastal development often interferes with natural processes resulting in enhanced erosion

• Engineering solutions to coastal erosion are often very costly and marginally successful

Miami , FLDevelopedBarrier Island

One in every three people on the planet now live within 100 kilometres of the sea

Two thirds of all the cities with over 2.5 million inhabitants are on the coast

In the US more than one-half the nation's population lives within 50 miles of the coastline, but coastal areas account for only 11 percent of the nation's land area.

In recent years, 40 percent of new commercial development and 46 percent of new residential development happened near the coast.

Coastal Erosion

North Carolina CoastAfter Huriicane Impact

Beach Nourishment

• Beach re-nourishment id one engineering solution to coastal erosion

• It involves transfer of offshore sand or sand from quarries to the coast are a cost of millions of dollars

• Many tourist beaches in the USA are there because of beach renourishment

Between 1995 and 2006, the Minerals Management Service provided over 23 million cubic yards of OCS sand for 17 coastal projects. These projects restored over 90 miles of the Nation’s coastline mainly in Florida, Maryland and Virginia

Central Boca Raton Beach Renourishment Project

Geologists are aware that the level of the ocean surface is not fixed, but instead a dynamic feature of our planet. Sea-level during the Last Glacial Maximum (LGM, 20,000 years ago) was 125 - 130 m lower than it is at the present time.

Using digital elevation data, geologists can develop maps showing the continental margins during episodes of lowered sea-level. The margin of the Gulf of Mexico and other parts of the western Atlantic as they would have appeared 20,000 years ago during the sea-level lowstand. Note that large areas of the continental shelf are exposed well above sea-level

Geologists can also model sea-level rise. Sea-level is 15 m higher than at present. Note the dramatic change in the outline of the Gulf of Mexico as much of south Florida is inundated. Also note that the Bahamas are completely submerged, and a narrow strip of land is all that remains of Cuba.

Both Moon and Sun Cause Tides

DEFINITIONS

• Tidal day – 24 hr 50 min – Time between successive phases of moon over a

given point on the earth• Tidal Period

– Time between two successive high or low tides • Tidal Range

– Difference between highest and lowest tide levels• Daily inequality

– Difference in height  between successive high orlow tides

TIDES

• Periodic changes in sea level relative to land along a coast

• Daily or Diurnal Tides– One high and one low tide each day

• Semi-daily or Semidiurnal Tide– Two high and two low tides of approximate equal

heights occur each day

• Mixed Tide– Two high and two low tides of unequal heights

(HHW, LHW, HLW, LLW)

TIDAL CURRENTS

• Horizontal water movement caused by tides

• Tides are like Shallow water waves • Orbital motion of water is highly elliptical:

can be assumed to be to and from motion • Flood tides when water moves in • Ebb tide when water moves back

The Bay of FundyNova Scotia, Canada

In the Bay of Fundy the tidal range can be up to 16m

TIDAL BORE