Oceans & Coasts Exam 2

Chapters 4, 5, & 6

Crest

the top of a wave

Trough

the bottom of a wave

Wavelength

the horizontal distance between two adjacent crests (or troughs)

Wave height

the vertical distance between a crest and an adjacent trough

Wave amplitude

half the wave height

Wave steepness

calculated by dividing the wave height by the wavelength

Wave period

a measure of the time it takes for a wave crest to travel between two points

Wave frequency

a measure of how many wave crests pass a specific point over time

Mechanical waves

involve a transfer of energy through a substance, and the substance is disturbed or temporarily deformed in the process; water waves are this

Capillary waves

very small waves; wave ripples; have a wavelength of 1.7cm or less and are produced when the wind blows over the water surface; restored by surface tension

Seiche

a special type of standing wave (oscillating waves); they slosh back and forth; the body of water must be partially bounded; form when winds blow across the length of a basin for a sustained period of time, pushing the water to one side, then when the wind stops the water goes back down, towards the other side; restored by gravity

Tsunami

the longest and fastest type of gravity waves; formed when a large volume of water is displaced, forming one or more large waves which radiate out in all directions; have very long wavelengths and very high speeds and can travel long distances; really only observable in shallow water;

can form in two ways: earthquakes and landslides (and collapsing glaciers)

Megatsunami

can form when very large landslide occur along the coast

Wind waves

waves where the energy originates from the disturbing force of the wind; transfers mechanicaal energy from the air to the water

Stoke’s drift

there is no significant net horizontal movement of water once a wave’s energy has passed by a given point; what leads to the formation of the surface currents

Wave base

found at a water depth of ½ the wavelength of the wave; once at this point, wave energy decreases to zero

Swells

waves generated in the open ocean; the waves you see constantly breaking on the shore; form hundreds of miles offshore in wave generation areas known as fetch

Fetch

wave generation areas hundreds of miles offshore

Fully-developed seas

forms when wind remains relatively constant for a long enough time; waves have reached their maximum possible size

Wave train

waves that that the same wavelength will move together in a group

Constructive interference

when two wave trains merge and are in phase with each other the waves will grow in size

Destructive interference

when two wave trains are out of phase with each other, they will cancel each other out

Extreme storm waves

form in association with powerful storms;

form in one of two ways:

1. focusing in time and space

2. current focusing

Rogue or freak waves

any wave more than twice the height of the significant wave heights of the waves surrounding it; can occur in relatively calm waters and rise suddenly out of nowhere

Deep water waves

waves operating in waters deeper than ½ their wavelength

Shallow water waves

when the water becomes shallower than ½ the wavelength; begins to slow down

Spilling breakers

form along coastlines with gentle beach slopes from waves with longer wavelengths. When the wave begins to break, turbulent foam and white water “spills” down the leading face of the wave; can break over long distances

Plunging breakers

the classic “pipeline” surfing waves; best developed from swells with long wavelengths that break along coasts where there is a sudden change in water depth

Collapsing breakers

a wave that collapses before the crest can ever break; most commonly found along coasts with a moderately steep beach slope

Surging breakers

Uprush

Backwash

Swash or Sea foam

Rup currents

Undertow

Onshore-offshore drift

Longshore transport

Beach drift

Longshore currents

Wave refraction