Tides and Waves

label each letter

A: wave height

B: amplitude

C: crest

D: wave length

E: trough

wave height (H)

vertical change between crest and trough

amplitude (A)

half the height

wavelength (λ)

distance between two crests or troughs

wave period (T)

time between two crests or troughs

frequency (v)

number of crests or troughs passing through a fixed point in 1 second

speed formula

λ x v (wavelength x frequency)

how do waves form?

when energy transfers to a body of water via wind or gravity

restoring forces of water (make it flat again)

gravity and surface tension

surface winds

generated by moving wind

tide waves

generated by gravitational pull of sun and moon

in which way does the wind pull water?

slightly horizontal in clockwise orbitals

deep water waves

don’t interfere with seafloor, form over water deeper than λ/2

shallow water waves

interfere with seafloor, form over water shallower than λ/2

swell waves

waves reaching the shore first

dispersion/sorting

faster, longer λ waves overtake shorter, slower λ waves

wave trains

formed by waves of similar speeds

types of wave interference

constructive and destructive

constructive interference

two waves in the same phase (both waves are in a crest or trough) meet and combine to create a bigger wave

destructive interference

two waves in different phases (one wave is in a crest and the other in a trough) meet and cancel each other out

refraction

deep water waves turn into shallow water waves at different parts along the shore

do waves refract towards or away from a headland (big rock)?

towards

dissipation

energy from waves dissipates as it goes into a bay 

types of shallow water waves

spilling, plunging, surging

spilling breakers

flat beach with fine sand and high biodiversity

plunging breakers

sloping beach with coarse sand and high biodiversity

surging breakers

steep beach with pebbles or rocks and no fauna except microscopic ones 

tsunamis

massive wave caused by offshore earthquake displacing the seabed, e.g. ache indonesia or tohoku japan

why does the tide retract before a tsunami?

the trough of a very high wave comes in first

diurnal tide

once per day

semidiurnal tide

twice per day

what forms the tide-producing force?

combination of the earth’s centrifugal force and the moon’s gravitational pull

why do tides move forward daily by 50 minutes?

the amount of time it takes for the earth (24hr orbit) and the moon (24hr 50min orbit) to realign

spring tide

greatest tidal range

neap tide

smallest tidal range

which letters represent high tide and which represent low tide?

high tide: A and G; low tide: D and J

which letter experiences diurnal tides, and which experiences semidiurnal tides?

A diurnal; B semidiurnal

amphidromic system

tidal wave rotates around a fixed point (amphidromic point)

which direction do tidal waves rotate in the N hemisphere?

counterclockwise

which direction do tidal waves rotate in the S hemisphere?

clockwise

tidal bore

rapid incoming tide coming into a narrow inlet faster than the water can move

exposure

the amount of energy a shoreline gets via waves

what is exposure governed by?

shore location, prevailing wind direction, fetch

fetch

distance that wind travels over open water

ballantine scale 1961

exposure scale for rocky shores

zonation

separation of species on a shore by their niche

a reflective beach has exposure

greater

a dissipative beach has exposure

lower

upper limit factors of zonation

abiotic; temperature, salinity, etc. 

lower limit factors of zonation

biotic; competition, adaptations, etc.