Oceanography Chapter 8

Why are these types of waves called internal waves?
Because they are internal to the ocean
Why are internal waves usually associated with a pycnocline?
Because a pycnocline is a boundary between two different water masses with different densities.
Besides where each type of wave is located, what is one of the most obvious physical differences between internal waves and surface waves?
Internal waves have a much longer wavelength as compared to the shorter wavelength surface waves.
Ocean waves in motion are classified as ______waves.
Of the following events, which is/are capable of generating waves?
Uplift or downdropping of the ocean floor
A storm moving over the ocean surface
A rock falling into a still pond
An underwater landslide
Human activities, such as a ship traveling across the ocean
Of the following statements about ocean waves, which is/are true?
Ocean waves can be described by their period, wavelength, and height.

Ocean waves can be classified by the way in which they form.

Ocean waves can be classified by the depth of water in which they move.

What is the crest of a wave?
the highest part of the wave
What is the trough of a wave?
the lowest part of the wave
What is the wave height?
the distance between the highest and lowest part of the wave
What is the wavelength?
the distance between consecutive crests or troughs
What is the wave period?
the time it takes for one wavelength of a wave to pass a particular point
How are wave period and wavelength related?
waves with shorter periods have shorter wavelengths
Which of the following statements about wave period is most accurate?
Wave period is the inverse of wave frequency.
Submarines sometimes ride out heavy storms in deep water by submerging. That is a practical application of utilizing the ____________________.
principle of decreasing orbital motion with depth
The celerity (speed) of a deep-water wave with a wavelength of 9 meters, relative to that of a deep-water wave with a wavelength of 1 meter, will be ______________.
You live on an island in the Pacific. An earthquake of magnitude 8.5 off the coast of Japan, 8000 km away, generates a tsunami with a wavelength of 200 km. The average water depth between your island and Japan is 4900 m. If a tsunami warning is issued for your island, how many hours will you have before the waves arrive?
10.14 hours
What is an interference pattern?
The wave pattern produced when two or more waves interact.
What results when two waves, in phase and with the same wavelength, interact?
A wave with an amplitude that is the SUM of the amplitudes of the initial two waves
What does the term “in phase” refer to?
Waves in phase have identical wavelengths and are aligned peak-to-peak and trough-to-trough
When will perfect constructive interference occur for waves that are in phase and moving at the same velocity?
When waves with identical wavelengths interfere
When will perfect destructive interference occur?
When two waves that are 180 degrees out-of-phase interfere.
What occurs more often, pure destructive, pure constructive, or mixed interference?
mixed interference
Which of the following are names for large ocean waves that can be created by constructive interference?
Rogue Waves
Freak waves
“Whitecaps” form when _____________________.
wave steepness reaches a ratio of 1:7
Destructive wave interference results in ___________.
reduced wave height
Of the following statements about ocean waves, which one(s) describe wave steepness?
Wave steepness is defined as wave height divided by wavelength.

If wave steepness ever exceeds a 1:7 ratio, then the wave breaks.

Of the following statements about ocean waves, which one(s) describe wave period?
the inverse of wave frequency

the time it takes for one full wavelength to pass a given point

Of the following waves, which one has the deepest wave base? Select only one answer.

A wave with a 1-meter wave height and a wavelength of 10 meters
A wave with a 2-meter wave height and a wavelength of 1000 meters
A wave with a 3-meter wave height and a wavelength of 100 meters
A wave with a 5-meter wave height and a wavelength of 100 meters
A wave with a 7-meter wave height and a wavelength of 100 meters

a wave with a 2-meter wave height and a wavelength of 1000 meters
Based on the equations for determining the speed of shallow-water waves, which one of the following variables is necessary to determine the speed of shallow-water waves?
water depth
Of the following physical changes that occur to waves as they move into shallow water, which is/are true?
Wavelength decreases.

Wave height increases.

Wave steepness increases.

The waves touch bottom.

How does water move as waves pass?
Water moves in a CIRCLE in the SAME direction as wave movement.
How does wave amplitude change with depth in water?
Wave amplitude decreases as depth increases.
What is the wave base?
the lower limit of wave-induced motion in the water
What is the relationship between wave base and wavelength?
The depth of the wave base is one-half the wavelength of the waves
Why does wave height increase as waves enter shallow water?
The ENERGY of the wave must be contained within a SMALLER water column in shallow water.
Why do ocean waves bend around headlands?
The waves are moving more SLOWLY just in front of the headland, causing the waves to bend.
What is refraction?
the bending of waves due to a change in wave velocity
How does wave refraction at headlands affect deposition and erosion?
Wave refraction at the headland INCREASES EROSION at the headland and causes deposition in adjacent bays.
As a wave approaches shore, its characteristics change by _____________________.
decreasing speed, increasing steepness
Waves usually arrive nearly parallel to the shore because ____________________________.
waves are refracted toward shallow water
How are tsunamis generated?
through displacement of the seafloor under water
What is a tsunami?
a series of water waves that travel away from a fault in all directions at high speed
Why do ships at sea tend not to notice tsunamis?
Tsunamis in deep water have SMALL wave height and LONG wavelength.
Why does the wave height of a tsunami increase as the tsunami enters shallow water?
In shallow water, the ENERGY of the tsunami must be contained within a SMALLER water column.
What type of plate boundary are most tsunamis associated with?
convergent plate boundaries
Which ocean is associated with most tsunamis?
Pacific Ocean
Will Sumatra experience another tsunami like the destructive one of December 2004?
This is likely, because Sumatra is near many ocean trenches.
A tsunami watch is issued by the Pacific Tsunami Warning Center when _______________________
an earthquake with a magnitude greater than Mw = 6.5 occurs beneath the ocean
Of the following offshore ocean conditions, which one(s) would likely produce spilling breakers?
a gently sloping rocky bottom

a gently sloping sandy bottom

Of the following situations involving orthogonals, which one involves the highest energy? Select only one answer.

Orthogonals that get farther apart as they approach the shore
Orthogonals that become more closely spaced as they approach the shore
Orthogonals that do not change much as they approach the shore
Orthogonals that disappear as they approach the shore
Orthogonals that become oriented parallel to shore as they approach the shore

orthogonals that become more closely spaced as they approach the shore
By how much would solar have to grow to match the current level of hydroelectric power?
about 60 times
Which source represents 32% of renewables?
none of them
Which energy source’s annual growth rate is about four times greater than that of tidal power?
Assuming that renewable energy sources will contribute more and more to power generation in the future, do you expect the growth rates for these renewable energy sources to increase or decrease over the next 30-year period (2000 to 2030)?
These growth rates are relative to small absolute numbers. They will most likely decrease as the total contribution by renewables increases.
Which projection has nonrenewables comprising roughly 50% of our energy production in 2050?
projection 2
Assume depletion of nonrenewables requires renewables (excluding combustibles and waste) to account for more than 30% by 2040. What growth rates of renewables must be achieved and by when?
at least 15% annual growth rate
A disadvantage shared by wave, solar and wind energy is that ___________________________.
it is not available on demand, and there currently is no viable way to store the energy
Of the following statements about tsunami, which is/are true?
At the coast, a tsunami looks like a suddenly occurring high or low tide, which is why they are misnamed “tidal waves.”

Tsunami are undetectable by ships in the open ocean.

Tsunami have a very long wavelength, so they travel at very high speeds (equivalent to the speed of a jet airplane).

The tsunami warning system uses seismic waves and deep-ocean pressure sensors to detect tsunami.

Which of the following best describes how scientists help the public prepare for an earthquake event?
scientists cannot predict when one will occur, but they can identify tectonically active areas that are likely to produce earthquake activity and let the public know if they’re in such an area