20.2 Ocean Waves A wave is the up and down movement of the oceans - - PowerPoint PPT Presentation

20.2 Ocean Waves

• A wave is the up and down movement of the
• ceans surface that is a form of energy that

moves across the water.

• Most waves are caused by winds.
• When the wind blows, it pushes on the oceans

surface, causing the water to lift.

• The stronger the wind the bigger the wave
• When a steady wind blows a wave train is

produced, which is a series of waves one after another moving in the same direction.

Wave Height and Speed

• Waves are measured by the vertical distance

between the top of a wave (crest) and bottom of the wave (trough)

• You can calculate the speed of a wave if you know

the wavelength and the period.

• The wavelength is the distance between 2 crests or

troughs.

• The period is the time it takes a wave to pass a

specific point.

• Formula is Velocity (V) = Wavelength (W)/Period

(P)

Waves Cont.

• When waves extend beyond the windy area they

generated from they have longer periods and more rounded crests.

• These are called swells.
• Swells can travel thousands of miles until they

reach the shore where their energy is released.

What causes waves to crash?

• As the wave approaches the shore it makes

contact with the ocean bottom slowing the wave down.

• This occurs when the waters depth is ½

the wavelength.

• When the water depth is less than one half of the

wavelength the top of the wave which moves faster than the bottom pitches forward and crashes.

Types of waves

• Waves can also break on the open sea, strong

winds produce narrow crests which are easily blown off by wind.

• The mixture of air and seawater produces a

white cap. This is a sure sign of bad weather.

• Sometimes during a storm a rough wave
• ccurs. These are large waves that are formed

when two waves unite or when waves hit

• pposite currents.
• These are extremely dangerous.

Tsunami’s

• A tsunami is a large wave caused by an

undersea earthquake.

• They can reach over 100 feet in hieght and can

travel as fast as 500mph

• A huge Tsunami hit the southern pacific in 2005

and cause thousands of deaths.

Waves

• The up and down

movement of the

• cean’s surface
• A disturbance which

moves through or

• ver the surface of a

fluid

• Mostly caused by

winds (Also earthquakes, volcanoes, grav. pull)

• Form of great energy

Wave Characteristics

• Parts of a Wave

 Crest = high point  Trough = low point  Height = vertical

distance from crest to trough

 Wavelength =

Horizontal distance between crest to crest

• r trough to trough

Wave period (P) : time for 2 crests to pass fixed point (P) Frequency (F) : F = wavelength / P (m/s) Wave steepness : H / wavelength When H / wavelength = 1/7 or angle at crest 120 or less = Breaker

Size of Wind Generated Waves

• Depends on 3 things:

 Wind Speed  Wind Duration (length of

time wind blows)

 “Fetch” Extent of open

water across which the wind can blow

Water Motion in Waves

• Water travels in vertical

circular orbits

• Wave moves, particles don’t!

Importance of Waves

• Shaping

Coastlines

 Erode cliffs  Grind rock into sand

• Ecology

 Returns O2 to water  Stir up food for filter

feeders

Types of Waves

CHOP – Short period (back bays) WHITECAP – a mixture of air and water from narrow wave crests blown by wind. SWELL – Rounded crests and Long period (boat rolls; seasickness) ROGUE – Formed when 2 or more large waves from a storm unite. Tidal Bore – a solitary wave that forms when the seafloor at the mouth of the river slopes gently and the tidal range is greater than five meters. SWASH – water up beach BACKWASH – back down

Caused by undersea quake or volcano

• Wavelength = ~150 mi.

Wave height = 6” – 1’ Can NOT perceive in boat Speed > 500 mph Slows down to ~25 mph at shore; water builds up to ~65+ ft

TSUNAMI “TIDAL WAVE”

Tsunami Waves

Creation of a Tsunami