Wave Erosion

What is a Wave?

AN OCEAN WAVE IS A RHYTHMIC RISE AN FALL OF THE WATER'S SURFACE.

Most waves we see are caused by wind.  When gusty storm winds blow across the surface of the water it creates ripples.  If the wind keeps up or blows over a long distance the ripples grow larger till they become waves.

 

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When we go to the beach, it appears that the waves are all approaching the shore head on, but this is not actually the case.  Most waves move towards the shore at an angle.  However, when the bottom of the wave line hits the bottom that part slows down, and the rest of the wave swings around until it all hits the shore head on.

THE BENDING OF THE WAVE AS IT APPROACHES THE SHORE IS CALLED REFRACTION.

 

 

Waves Cause Erosion

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AS THE WAVE CRASHES, IT MOVES UP ONTO THE BEACH IN A MOTION CALLED SWASH.  SWASH MOVES SAND AND OTHER SEDIMENT UP ONTO THE BEACH AND DEPOSITS IT.

AFTER THE WAVE MOVES AS FASR UP THE BEACH AS IT CAN, BACKWASH PULLS IT BACK TOWARD THE WATER TAKING SEDIMENT WITH IT.

The motion of waves, swash, and backwash create currents which run along the shore.  These currents behave just like rivers, so they transport sediment of all types.

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UNDERTOW IS A STRONG BACKWASH CURRENT THAT RUNS ALONG THE BOTTOM OF INCOMING WAVES.  If you have ever stood on the beach and allowed waves to crash on your feet you are familiar with undertow.  It is the pull you feel as the wave retreats back towards the water.

RIP CURRENTS ARE STRONG SURFACE CURRENTS THAT FLOW AWAY FROM THE BEACH.  These are very dangerous for swimmers b/c they can pull people out to sea.  Luckily, they only form in narrow bands, so if you swim parallel to the shore, you can escape the rip current and swim safely in.

Landscape Features Created By Wave Erosion

Sea Cliffs

SEA CLIFFS FORM ALONG COASTS AS WAVES WEAR AWAY THE ROCK BELOW THE HIGH TIDE MARK. This constant wearing away of rocks near the water creates an overhang, which eventually collapses to form a vertical cliff leading into the sea. 

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Sea Caves

SEA CAVES FORM IN SEA CLIFFS WHEN A HOLE IS WORN INTO THE CLIFF CREATING A CAVE.

 

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Arches

ARCHES FORM WHEN A SEA CAVE IS WEATHERED AWAY LEAVING ONLY THE OPENING STANDING.

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Sea Stacks

SEA STACKS FORM WHEN THE TOP AN ARCH COLLAPSES LEAVING THE TWO SDES STICKING UP OUT OF THE WATER.

 

Shoreline Features Created by Wave Deposition

BEACHES

SOME OF THE SEDIMENT CARRIED UP ONTO THE LAND BY SWASH IS DEPOSITED CREATING A BEACH. 

A BEACH IS THE AREA BETWEEN THE HIGH-TIDE AND LOW-TIDE LEVEL ON A COASTLINE.

They may be sandy, pebbly, or even rocky.  The composition of the beach depends on the material that’s available, and the slope of the shoreline.  If the seafloor is steep then all of the sand and clay are easily washed away from the beach by backwash, and all that’s left at the beach is pebbles.  If the seafloor has a gentle slope, then only clay gets washed out and a sandy beach forms. 

Most sand grains at the beach are made from durable minerals like Quartz and Feldspar, but may contain mica and magnetite, depending on the prevalence of minerals in an area

 

SANDBARS

A SANDBAR IS A SHALLOW SANDY AREA IN THE WATER OUT FROM THE BEACH.  THEY ARE CREATED BY SAND DEPOSITED BY UNDERTOW AND BACKWASH CURRENTS.  

 

 

 

BARRIER ISLANDS

BARRIER ISLANDS ARE SIMILAR TO SANDBARS, EXCEPT THEY ARE LARGER AND EXTEND LONGER DISTANCES.  

The formation of barrier islands is believed to be a combination of glaciers depositing sediment at the end of the last ice age, and waves continually depositing sediment.  Barrier Islands are important because they protect coastlines from storms and flooding, and create sheltered harbor habitats. 

 

 

SPITS

WHEN A SANDBAR FORMS ACROSS THE MOUTH OF A BAY IT IS CALLED A SPIT.

HOOKS

AFTER A LONG TIME OF BEING BOMBARDED BY CURRENTS AND WATES, SPITS GET BENT INWARD TOWARDS THE SHORE CREATING A SHORELINE FEATURE CALLED A HOOK.

Jamaica Bay is a lagoon on the Rockaway coast protected by the Rockaway Beach hook.