short-term processes: second and third order features
- physical
- chemical
- biological
 

Physical Processes

Waves at the Coast

When the ocean/atmosphere interface is disturbed, a wave is produced; the three primary forces that produce surface waves are wind, earthquakes, and gravitational attractions

Parts of a wave:
- crest
- trough
- wave height (H)
- wavelength (L)
- steepness (H/L)
- wave period
- frequency
- ripples (waves with periods less than 1s); as soon as the wind has a surface to push - ripple - it transfers more energy to this surface and the waves begin to increase in size

When the steepness ratio reaches 1:7, the wave is unstable and breaks

The size of the wave is determined by the speed, duration, and fetch of the wind
 

The Motion of Water in a Wave

water moves in a circular or orbital path in a wave, moving forward on the crest and backward on the trough

the diameter of the orbital path is equal to the height of the wave; below the surface of the wave, the orbital paths decrease in diameter, until there is no motion at 1/2 wavelength
 

Wind Waves and Swell

as the wind velocity increases and waves absorb the wind's energy, teh wavbes grow higher and their periods become longer - storm waves; generally 50-100 m in length in open ocean; storm waves may become twice that long; rogue waves may reach up to 40 m in height quickly developing from a pileup of small storm waves

when waves are no longer influenced by the winds, the waves that persist are called swells; sam origin as wind waves, but have have out-travelled them; swells, like the wind-driven waves, are gravity waves with considerable power that produce the huge surf in Hawaii and southern California
 

Approaching the Shore

The orbital path of the water comes into contact with the seafloor when coming closer to shore; the bottom friction makes the wave travel slower - the wavelength decreases and the wave steepness increases; the water is squeezed into an eclipse and the bottom of the waves slows causing the wave to become unstable; the wave crest topples forward and collapses - breaking
- plunging breakers - gradually gaining steepness and height
- spilling breakers - produced by wind waves entering shallow water
- collapsing breakers - swell waves that break on steep beaches that are hard to distinguish from spill breakers
- surging breakers - a wind wave that steepens instead of spilling and runs up the beach

As approaching waves encounter the features of the shoreline - sandbars, rocky outcrops, cliffs, breakwaters - they respond like light waves
 

Reflection

A wave that bounces of a vertical wall or cliff retains almost 100% of its energy, but the wall would eventually break down; breakwaters built in deep water to protect ships in a harbor reflect waves back to sea before they have a chance to break; the amount of reflection is proportional to the steepness of the obstruction
 

Diffraction

Some of the wave energy spreads behind an obstacle such as a breakwater
 

Refraction

typical of waves approaching at an acute angle; as it approaches, the parts of the wave front that reach shallow water first are slowed down and the part still in deeper water continue to move rapidly - slowing takes place at different times along the front of the wave; the result is a bending or refraction which tends to line up each portion of the wave parallel to the shore

waves tend to converge on a headland and dissipate in an embayment

Orthogonals: lines drawn perpendicular to each wave front