7/21/2019 Coastal Erosion Mini

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Coastal Erosion:

•  Erosion - the wearing away and removal of material

•  Deposition - the dropping of material

•  Abrasion - the wearing of rock due to rock fragments being hurled against cliffs

•  Attrition - the breakdown of rocks as they hit against each other

•  Hydraulic Action - the force of waves causing rocks to split apart as waves compress air

in cracks in the rocks

• Wave Pounding - sheer force of water hitting rocks

• Solution - where minerals in rocks are dissolved by the action of sea water.

•  Longshore Drift - the movement of material along a coastline.

When a wave breaks, water is washed up the beach - this is called the swash. Then

the water runs back down the beach - this is called the backwash.

Constructive waves:• They are created in calm weather and are less powerful than destructive waves.

• They break on the shore and deposit material, building up beaches.

• They have a swash that is stronger than the backwash.

• They have a long wavelength, and are low in height.

Destructive waves:

• Destructive waves are created in storm conditions.

• They are created from big, strong waves when the wind is powerful and has been

blowing for a long time.

• They occur when wave energy is high and the wave has travelled over a long

fetch.

• They tend to erode the coast.

• They have a stronger backwash than swash.

  They have a short wave length and are high and steep.

 

• CREST is the uppermost part of the wave.

• FETCH is the distance that the wind travels against a wave.

• FREQUENCY or wave period, is a measure of how many times something happens

over a set period of time.

• TROUGH is the lowest point of the wave.

• WAVELENGTH is the horizontal distance between one crest and the next crest (or

trough to trough).

• WAVE HEIGHT is the vertical distance between a wave’s crest and trough.

Coastal transport:

•

Suspension-fine sediment is carried as a suspension in the water, making it dark, murkyor muddy.

• Solution-dissolved material is carried along in a solution, so you can’t see it.

• Traction- Larger pebbles and cobbles rolled along the seabed.

• Saltation- Small pebbles are moved when one pebble hits another, causing it to bounce.

This bouncing can set up a chain reaction.

• Waves will widen weakness or cracks in the rock face by the processes of hydraulic

action, wave pounding, abrasion and solution. Gradually these cracks get larger,

developing into small caves.

• A sea arch forms when sea caves merge from opposite sides of a headland. If the arch

collapses, a pillar of rock remains behind as a sea stack.

• Beaches: are common features of a coastline. Beaches are made up of eroded material

that has been transported from elsewhere and deposited by the sea. Most waves

break near the shoreline, so sediment near the water is more effectively broken

down by attrition. Sandy beaches have gently sloping profiles and shingle and

pebble beaches are steeper.

•  A spit is an extended stretch of beach material that projects out to sea and is joined to

the mainland at one end.

• Spits are formed where the prevailing wind blows at an angle to the coastline, resulting

in longshore drift. Over time, the spit grows and develops a hook if wind direction

changes further out. Waves cannot get past a spit, which creates a sheltered area

where silt is deposited and mud flats or salt marshes form.

• Baymouth bar: A narrow ridge of sand that stretches completely across the mouth of a

bay.

• Lagoon: an area of shallow water separated from the sea by low sandy dunes.

• Sea wall: A concrete wall or embankment erected to prevent the sea from encroaching

on or eroding an area of land.

• Rock armor: A loose assemblage of broken stones erected in water or on soft ground as

a foundation.• Rock barrier:

• Groyne: a protective structure of stone or concrete; extends from shore into the water to

prevent a beach from washing away.

• Beach Replenishment: Replacement of beach sand removed by ocean waters. Sediment

from other areas is supplied by mechanical means to supplement sand on an

existing beach or to build up an eroded beach.

 

Coral Distribution: Found all around the world in both shallow and deep water but

reef-building corals are only found in shallow tropical and subtropical waters

because the algae found in their tissues need light for photosynthesis and they prefer

water temperatures between 22 and 29C. There are also deep sea corals that thrive

in cold, dark water they have different algae and do not need sunlight or warmth to

survive.

• Global Threats: the greatest threats to reefs are rising water temperatures and ocean

acidificatio n linked to rising carbon dioxide. H igh temperatures causes the corals to

lose their algae’s that produce the food corals need- condition known as coral

bleaching. The acid seawater makes it more difficult to build up their calcium

carbonate skeletons, and if the acidification was severe enough it could even break

apart the excising skeleton that already provides the structure for reefs.

• Local Threads: Overfishing and overharvesting of corals also disrupt reef ecosystems.

Boat anchors and divers can also scar reefs. Invasive species like Lion fish to:

through consumption of and competition with native coral animals.

Runoff from lawns, sewage, cities, and farms feeds algae that can overwhelm reefs.

Deforestation hastens soil erosion, which clouds water- smothering corals.

• Coral Bleaching: This occurs when coral polyps lose their symbolic algae called

zooxanthellae. Without this the living tissues are almost transparent and you can seeright through their stony skeletons, which is white; hence the name coral bleaching.

It can be caused by- water that is to hot or cold- to much or to little light- or the

dilution of lots of sea water by lots of fresh water- the biggest cause today is the

rising temperature.