Waves in the Sea

Objectives:

1.    Explain what causes waves

2.    Identify features of waves.

3.    Describe wave motion.

4.    Identify how waves affect coastal landforms.

Notes:

As we learned earlier in the semester, a wave transfers energy without any net movements of the medium.  additionally, all waves have a crest, trough, frequency and wavelength.  Using this definition we can describe the waves in the ocean as a rhythmic rise and fall of the water's surface.  The energy that is transferred by the motion of the waves erodes and shapes the coastlines.  There are three main mechanisms for the formation of waves.

wind - most waves are created this way
depends on three factors
 wind speed - kinetic energy being transferred into the ocean length of time the wind blows - increases the nit kinetic energy fetch - the width of the water body
seismic activity - most destructive and not too common (tsunami)
the moon's gravity - creates the tides

Properties of waves

Although the net movement of a waves is a straight line, the medium in water waves travel in circular motion

(pao.cnmoc.navy.mil/educate/ neptune/images/motion.gif)

Refraction of Ocean Waves:

Refraction is a property of waves exhibited as waves bend around areas of different densities.  It can be seen as light bends around the atmosphere and as waves are deflected sideways at the beach.

the refraction of the ocean waves occurs as the trough of the waves scrapes the bottom of the shallow coastline
 causes the wave to slow down (friction) the oncoming (faster) waves impact the back of the waves and push them causing the refraction

(hypertextbook.com/.../refraction/ ocean-wave-refraction.png)

Breakers

When a wave collapses on the beach it is called a breaker.  it is caused by the following conditions:

the trough drags on the bottom causing the crest to pass it
when the water is no longer able to support the accelerating crest, the wave collapses
 usually at a depth ~ 1.3 times the height of the waves

Shoreline Currents

Swash - the gentile water that runs up the beach after the wave breaks
 Occurs at an angle to the shoreline
backwash - the return of the swash to the ocean
 returns perpendicular to the shoreline rip currents form when breakers bring in more water than the backwash can return

The buildup of water behind the breakers, swash, and backwash creates a parallel current called a longshore current.

 movement is parallel to the beach important to the movement and deposition of sand responsible for the creation of sandbars

(life.bio.sunysb.edu/ marinebio/rip.jpg)