WAVES - O'Mara's Science...

WAVES

• Up and down movement of ocean surface• Transportation of energy across the water over vast distances •If not stopped by anything, waves can travel entire oceans • Size and speed depend upon: WIND SPEED LENGTH OF TIME WIND BLOWS (Duration) DISTANCE OVER WHICH IT BLOWS (Fetch)

Water is not moving horizontally, butvertically or up & down.

The ENERGY of the wave is transferred horizontally.

Ocean waves are visual proof of the transmission of energy across the surface of the ocean.

How tall is a wave? Wave height is measured from crest to trough.

Crest - Very top of the wave Trough - Hollow between 2 crests

~~~Wavelengths ~~~ Wavelengths are measured from the crest of one

wave to the crest of the next wave.

Period Period is the amount of time across a

wavelength. The time from wave to wave. To do this, measure the time from when the

first crest hits until the next crest hits the same point.

Wave Velocity

Velocity is the speed of the wave velocity = distance

time

To do this, measure the wavelength, then divide by the period.

Wind Strength - wind must be moving faster than the wave crests for energy transfer to continue

Wind Duration - winds that blow for a short time will not generate large waves

Fetch - the uninterrupted distance over which the wind blows without changing direction

Factors Affecting Wave Height

Fetch Fetch is distance over which the wind blows in one

direction.

Wave Heights

•If speed is slow, wind duration & fetch do not matter, so the wave will be SMALL

•If wind speed is great, but it only blows for a short period of time or over a short fetch, then the wave will be SMALL

•If wind speed is great and duration and fetch are long, then the wave will be LARGE

What Causes Waves?

•Most common cause = Wind• In particular the friction between the water & the wind as it passes over

•Underwater earthquakes, landslides, & volcanoes = Tsunami• Gravitational pull of sun on the moon = Tidal Waves

Why do waves break? Water particles move in circular patterns called orbits.

When the depth of the water is less than 1/2 the wavelength, the wave hits bottom. The length rolls over to become the height and the wave breaks. As the wave moves from deep water to shallow, “vertical” circles become flat as it approaches the shore.

Interactions with Shore

•Surf zone - where swell forms breakers

Types of Waves

•Spilling Breakers - gently sloping coasts, where waves break slowly & over long distances, crest spills gently•Example - Georgia coasts, Florida beaches

•Plunging Breakers - steeper coasts, waves slow more quickly & crest curls way over the front of the wave & plunges to the base•Example - Hawaii, Australia

•Surging Breakers - very steep coastline, waves build suddenly & break right onto the beach•Example - cliff sides

Plunging surf (curling motion) occurs where the slope toward the shoreline (bottom) is steep. These

are the best surfing waves. Plunging waves lose energy faster than spilling waves.

Spilling surf occurs where the slope toward the shoreline (bottom) is gradual. Spilling waves lose

energy more slowly than plunging waves.

Deep Water Waves, Shallow Water Waves

Note the importance of the relationship

between wavelength and depth in determining

wave type.

STORMS SWELL SURF(energy in) (energy out)(waves move away from the sea

that generated them; this energy can travel across an entire ocean basin like the Pacific Ocean)

SwellsWaves extending beyond the windy area where first generated

• Longer periods

• Rounded crests

• Travel for thousands of km until they reach shore

•Ex. Antarctica to

Alaska (6,000 miles)

Whitecaps•Waves breaking on open ocean

•Crest blown off by wind

•Mixture of air and water forms white foam

•Indicate rough weather

Rogue Waves• Unusually tall waves (up to 10 stories high) appearing in a set of smaller waves• Short lived, unexpected, unpredictable• Form when two or more large waves unite or when waves meet opposing currents•“Walls of Water” -

Rogue WavesThis shows an oil tanker encountering a rogue wave. A deep trough, or “hole in the ocean” as it is called, drops 15m below

the still water line. The bow of the vessel is then over taken by the large crest, that might be 15m above the still water

line. The huge amount of water causes major damage to the ship and might even cause it to sink.

What happens when waves from different storm systems exist simultaneously?

When waves meet up, they interfere with one another.

Wave interference can be:

Destructive interference – two waves that cancel each other out, resulting in reduced or no wave

Constructive interference – additive interference that results in waves larger than the original waves

Rogue waves - these freak waves occur due to interference & result in a wave crest higher than the theoretical max

Interference And Rogue Waves

Interference

Tsunamis• Long, high ocean waves•Caused by earthquakes, landslides, & volcanoes erupting underwater• In deep oceans, they are relatively hard to see•The water is so deep & waves are moving so fast that the wave height is very small

•Closer to shore, the ocean depth and speed decrease, the energy can’t go anywhere but up creating a very large & dangerous wave•80% happen in the Pacific Ring of Fire

Tsunamis•Trough often reaches shore first, producing a vacuum effect that sucks coastal water seaward and exposes harbor and sea floors. •Retreating of sea water is an important warning sign as the wave’s crest and its enormous volume of water typically hit shore five minutes or so later.

•Usually composed of a series of waves, called a wave train, so its destructive force may be compounded as successive waves reach shore.•Some do not appear on shore as massive breaking waves, but instead resemble a quickly surging tide that inundates coastal areas.

Tsunamis vs Wind WavesTsunamis Wind Waves

Speed 500-600 mph 5-65 mph

Wave Height (avg)

45 ft 3 ft

Wavelength 60-300 miles 300-600 ft

TsunamisBy the time they reach the shore and break, the wave

height may be 100 ft. high and may travel at 400 miles/hour

Major wave tsunami in Laie Point, Oahu, Hawaii produced

by an earthquake in the Aleutian Islands (Alaska)

March 9, 1957. The highest wave in this event was 3.6 m

(11.8 ft) above sea level.

Boxing Day Tsunami - December 26, 2004

•Caused by a magnitude 9.1-9.3 megathrust earthquake where the Indian plate subducted into the Burman plate•Earthquake lasted 8.5 minutes and sent devastating tsunami’s to all countries bordering the Indian Ocean; epicenter was near mainland Indonesia•Killed 230,000 in 14 countries•Most impacted - Indonesia, Sri Lanka, India, & Thailand•There was no effective Tsunami Warning System in place for the Indian Ocean at that time

Time Travel Map •NOAA's tsunami travel time (TTT) map -Map contours represent 1-hour intervals. Red indicates 1- to 4-hour arrival times, Yellow indicates 5- to 6-hour arrival times, Green indicates 7- to 14-hour arrival times, and Blue indicates 15- to 21-hour arrival times..

World’s deadliest hit March 11, 2011• The world’s 4th largest earthquake

since 1900 & largest in Japan • Magnitude 9.0 underwater

earthquake• Entire Pacific Rim was issued a

Tsunami Warning (except mainland US & Canada)

• Produced a wave 40.5 meters in height that travelled 10 km inland

• Earthquakes moved Honshu 2.4m east & shifted the Earth on its axis somewhere between 10-25cm

• 20,000 people were confirmed killed/missing

• Caused multiple hydrogen explosions & caused a nuclear meltdown at Fukushima Nuclear Power Plant in Japan

Low tide (a) and high tide (b) at The Rocks

Provincial Park, Hopewell Cape, New Brunswick

(Canada).

The tidal range at the head (opening) of the bay exceeds 10 m (28 ft)!

Tides

Internal Waves

Waves that occur at the boundaries of water layers with different densities are called internal waves.

Wave Refraction, Diffraction, & Reflection

•Wave Refraction - the slowing and bending of waves in shallow water.

•Wave Diffraction - propagation of a wave around an obstacle

•Wave Reflection - occurs when waves “bounce back” from an obstacle they encounter. Reflected waves can cause interference with oncoming waves, creating standing waves.

Wave Refraction

Wave Diffraction

Harnessing Wave Energy• Renewable Natural Resource

(Alternative)• Can only be generated around coastal

areas• Most is focused in Pacific Northwest• Clean, pollution-free energy source• Different than tidal power

• Special buoys & turbines capture the power of waves & tides and convert them to electricity

• Both vary depending on nature, but are more predictable than wind• Waves are produced through wind• Tides are produced through gravitational pull

Harnessing Wave Energy Water entering the top of the wave generator

causes the turbine to spin which will produce electricity

Lockeed Corp’s Dam-Atoll