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119 Cards in this Set
- Front
- Back
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how do all ocean waves begin?
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as disturbances caused by release of energy
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what's the most significant cause of ocean waves?
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wind
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how do waves transmit energy through matter?
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by oscillatory motion
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what are 2 types of progressive waves?
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longitudional and transverse (orbital is a combination of the 2)
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what happens to circular orbital motion with depth?
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it decreases
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what happens at the wave base?
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water motion ceases entirely
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where is the wave base?
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at 1/2 the wavelength
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if water depth is greater than 1/2 the wavelength, the wave is known as a....
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deep water wave
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if water depth is less than 1/20 of wavelength, the wave is known as a....
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shallow water wave
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what is the wavelength range of transitional or intermediate waves?
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2d < L < 20d
(d = depth, L = wavelength) |
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the wavelength of capillary waves is less than what?
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1.74 cm
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the wavelength of gravity waves is greater than what?
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1.74 cm
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what is the dominant restoring force of capillary waves? gravity waves?
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capillarity; gravity
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what are 3 factors that influence the size of wind generated waves?
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wind speed, duration (time), and fetch
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what is a fully developed sea?
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an equilibrium condition that is reached when the maximum wave height is achieved for a particular wind speed, duration, and fetch
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what is swell?
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uniform, symmetrical waves that transmit energy from the sea across the ocean
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what are rogue waves caused by? aka superwaves
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constructive interferene
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when do waves release energy near the surf zone?
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the steepness exceeds 1:7 ratio?
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if the height of a wave is 7 m, what must the minimum wavelength be so the wave doesn't break?
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49 m
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what are spilling breakers?
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waves that break on a relatively flat surface
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which waves are best for surfing? why?
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plunging breakers; 'cuz they have curling crests
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what happens when swell approacehs the shore?
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segments of the waves that first encounter shallow water are slowed, where as other parts unaffected by the shallow water move ahead, causing the wave to refract, or bend
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why is refraction significant?
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it concentrates wave energy on headlands
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what is a standing wave?
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an interference pattern caused by reflection of waves off seawalls or other barrier; crests do not move laterally as in progressive waves but alternate with troughs at antinodes
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what happens between the nodes and antinodes of a standing wave?
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there is no vertical water movement
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how are tsunami, or seismic sea waves caused?
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by sudden changes in the elevation of the sea floor, such as from fault movement or volcanic eruptions
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tsunami often have lengths exceeding _____ meters
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200
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where do most tsunami occur?
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in the pacific
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why is The Pacific Tsunami Warning Center (PTWC) important?
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it has dramatically reduced fatalities by successfully predicting tsunami using real time seismic information
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True or False? In shallow-water waves, wave speed increases with increased water depth, while in deep-water waves, wave speed increases with increased wavelength.
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True
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True or False? In the ocean, a rogue wave is also known as "swell."
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False
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True or False? Internal waves are usually found in areas where there is a strong, permanent pycnocline.
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True
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True or False? Internal waves can sometimes exceed heights of 100 meters and can carry matter to great depths.
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True
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True or False? The superposition or overlapping of two waves always results in destructive interference between the different waves.
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False
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True or False? Waves always travel in the same direction as the prevailing current, even far offshore.
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FAlse
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True or False? When a tsunami reaches a coastal area, it is always represented by a single rapid surge of water toward the shore, resembling a suddenly-occurring high tide (which is why they are misnamed "tidal waves").
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False
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What is wave refraction?
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the bending of waves as they approach a coastline
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If a tsunami leaves the Hawaiian Islands travelling toward the west coast, how long will it take to arrive?
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5 hours
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these waves are also known as push pull waves
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longitudinal
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what type of a wave is sound?
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longitudinal
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True or False: energy can be transmitted through all states of matter (solid, liquid, gas) by longitudinal movement of particles
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True
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these waves are aka side to side waves
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transverse
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tying one end of a rope to a doorknob while the other end is moved up and down or side to side is example of this type of wave motion...
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transverse
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what is the period of most wind generated waves?
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0 sec - 5 minutes
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what is the period of most tsunami?
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5 min to 12 hrs
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what is wave steepness?
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waveheight/wavelength
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what steepness ratio must be exceeded for a wave to break?
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1:7
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how is wave speed defined?
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wavelength/period
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what is the speed of a deep water wave, in m/s?
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1.25 * sqrt(wavelength)
wavelength in m |
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what is the speed of a deep water wave in m/s in terms of its period?
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1.56 * Period
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for deep water waves, the shorter the wavelength, the faster the wave travels?
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false; (longer wavelength)
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True or False: for a deep water wave, the wave speed depends ONLY on the wavelength
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True
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the wave speed in m/s of a shallow water wave in terms of the water depth, d, is.....
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S = 3.13 * sqrt(d)
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True or False: for shallow water waves, the deeper the water, the faster the wave travels
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True
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give 2 examples of shallow water waves
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tides, tsunami
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True False: for shallow water waves, the speed depends solely on water depth
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true
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True or False: for intermediate waves, the speed depends solely on wavelength
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false; (wavelength and water depth, since they're INTERMEDIATE)
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what are whitecaps?
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open ocean breakers that form when steepness reaches a critical value of 1/7
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a Beaufort number of __ would be classified as a hurricane
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12
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a Beaufort number between __ and __ would indicate a breeze
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1-5
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a Beaufort number between __ and ___ woudl indicate gale
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6-9
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a Beaufort number between __ and ___ woudl indicate a storm
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10-11
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what was the height of the largest authentically recorded wind generated wave?
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34 m (112 feet), which contradicted the 60 ft rule
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what is wave dispersion?
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the sorting of waves by wavelength
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what is the decay distance?
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the distance over whcih waves change from a choppy "sea: to uniform swell, which can be up to several hundred kilometers
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what are interference patterns? give 3 examples
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when swells from different storms run together, the waves clash and interfere w/ one another; constructive, destructive, mixed
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what is an example of a free wave?
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swell
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what is a free wave/
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a wave moving with the momentum and energy imparted to it in the sea area but it is not experiencing a maintaining force that keeps it in motion
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what is a forced wave?
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it's maintained by a force that has a periodicity coninciding with the period of the wave
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what are rogue waves?
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massive, solitary waves that can reach enormous height and often occur at times when normal ocean wave are not unusually large
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what is the probability of a rogue wave?
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one/billion
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in what conditions do rogue waves occur?
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when storm driven waves move against strong ocean currents, causing the waves to steepen, shorten, and become larger
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where do conditions for rogue waves occur?
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along the SE coast of Africa, where the Agulhas current flow directly against large Antarctic storm waves, creating rogue waves
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what was the worst disaster in the history of yachting?
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the 1979 Fastnet Race, from the English Channel to Ireland and back
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name 2 yachting disasters
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2. Fastnet in 1979
1. Admiral's Cup Series races from Sydney to Hobart in 1998 |
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what is the surf zone?
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the zone of breaking waves
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what do breaking waves indicate near the coast?
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shallow water
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what happens to the speed, wavelength, and wave height as a wave enters shoaling (shallow) water?
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speed decreases, wavelength decreases, wave height increases (increase in steepness)
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what is a handy way of estimating water depth in the surf zone?
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the depth of water where waves are breaking is 4/3 times the breaker height
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what causes a wave to topple over and break/
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at the surface, individual water particles have not felt bottom, so the top part travel faster than the bottom part => top part overruns the bottom part and the wave breaks
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these types of breakers are a result of gently sloping ocean bottom, which extracts energy from the wave more gradually, producing a turbulent mass of air and water that runs down the front slope of the wave instead of producing a spectacular cresting curl
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spilling breaker
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this type of breaker has a curling crest that moves over an air pocket; they form on moderately steep beach slopes; best for surfing
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plunging breaker
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this type of breaker occurs when the ocean bottom has an abrupt slope, and wave energy is compressed into a shorted sistance and the wave will surge forward; board surfers tend to avoid them
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surging breaker
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how is a surfer propelled forward by the wave's energy?
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surfers balance the force of gravity, which is directed downward, with the buoyant force (perpendicular to the wave face)
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why do all waves come in straight toward a beach despite their original orientation?
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cuz of refraction
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what do orthogonal lines indicate?
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how energy is distributed along the shoreline by breaking waves
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how are orthogonal lines different in headlands and bays?
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they converge on headlands and diverge in bays
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what is the surf zone?
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the zone of breaking waves
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what do breaking waves indicate near the coast?
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shallow water
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what happens to the speed, wavelength, and wave height as a wave enters shoaling (shallow) water?
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speed decreases, wavelength decreases, wave height increases (increase in steepness)
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what is a handy way of estimating water depth in the surf zone?
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the depth of water where waves are breaking is 4/3 times the breaker height
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what causes a wave to topple over and break/
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at the surface, individual water particles have not felt bottom, so the top part travel faster than the bottom part => top part overruns the bottom part and the wave breaks
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these types of breakers are a result of gently sloping ocean bottom, which extracts energy from the wave more gradually, producing a turbulent mass of air and water that runs down the front slope of the wave instead of producing a spectacular cresting curl
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spilling breaker
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this type of breaker has a curling crest that moves over an air pocket; they form on moderately steep beach slopes; best for surfing
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plunging breaker
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this type of breaker occurs when the ocean bottom has an abrupt slope, and wave energy is compressed into a shorted sistance and the wave will surge forward; board surfers tend to avoid them
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surging breaker
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how is a surfer propelled forward by the wave's energy?
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surfers balance the force of gravity, which is directed downward, with the buoyant force (perpendicular to the wave face)
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why do all waves come in straight toward a beach despite their original orientation?
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cuz of refraction
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what do orthogonal lines indicate?
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how energy is distributed along the shoreline by breaking waves
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how are orthogonal lines different in headlands and bays?
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they converge on headlands and diverge in bays
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how does diffraction result?
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from wave energy being transferred around or behind barriers that impede a wave's forward motion
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in wave reflction, the angle of incidence = _____ __ __________
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the angle of reflection
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an outstanding example of wave reflection occurs where?
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in an area called "The Wedge" which develops west of the jetty that proects the harbor entrance at Newport Harbor, California
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in "The Wedge", wave height often exceeds what? what types of breakers does it produce?
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8 m; plunging breakers that are way 2 challenging for surfers
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when are standing waves produced?
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when waves are reflected at right angles to a barrier; they're the sum of 2 waves with the same wavelength moving on opposite directions, with no net movement
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what are nodes?
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lines along which there is no vertical movement?
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what are antinodes?
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crests that alternately become troughs, which are the points of greatest vertical movement within a standing wvae
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how are most tsunamis caused?
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by fault movement
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do fault movements that produce horizontal or vertical displacements generate tsunami?
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vertical, because it changes the volume of the ocean basin, and affects the entire water column; horizontal movement is side to side and does not change the water column volume and does not generate tsunami
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how fast do tsunamis move?
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more than 700 km/hr in open ocean
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True or False: the first surge of a tsunami is always the largest
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false
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True or False: many small tsunami are generated each year and go largely unnoticed
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true
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on average, how many tsunamis occur each decade?
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57
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almost __% of all great wavesare generated in the pacific ocean
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86
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when was Krakatau?
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Aug 27, 1883
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how many were killed by the Krakatau explosion and subsequent tsunami?
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36,000 (over 1000 villages drowned)
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what was Hawaii's worst natural disaster?
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a tsunami that hit Hilo on Apr 1, 1946: M_w = 7.3 earthquake in Aleutian Trench caused it; $25 million damage and 159 killed
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list 3 nations that expereience more tsunami than any other place on earth, in order
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1. Japan
2. Chile 3. Hawaii |
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What is the record height of a tsunami?
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Ryukyu Islands, South of Japan in 1971: normal sea level was raised by 85 m
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what was the most deadly tsunami?
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Aura, Japan, 1703: 100,000 deaths
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