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136 Cards in this Set

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ways that the bathymetry of the ocean has been measured
sounding-letting a weight come out of a ship and hit the bottom
sonar
topography from satellite
problems with soundings
boat drifting
current in lower layers
why is there a density difference between continental and oceanic crust
continental crust is composed of granite, which is lighter than the basalt that makes up oceanic crust
Explain the topography around a continent and extending into the ocean
there is a shallow continental shelf, leading to a shelf break, continental slope, and eventually either to a trench, contiental rise, or abyssal plain
evidence for plate tectonics
earthquakes
similarities between species across basins
age of ocean crust
magnetic anomalies
hot spots
what causes the movement of lithospheric plates
convention in the mantle caused from heat from radioactive decay at the core of the earthg
why is oceanic crust more dense the farther it is away from a ridge
because as it cools, the rock beceomes more dense and also it accumulates sediment that makes it heavier
what land location is where convergent boundaries are usually found
on coastlines where ocean meets continental crust
are volcanoes found at convergent or divergent boundaries?
convergent. a lot of the oceanic crust which contains water and sediment that has a lower melting point, begins to melt from the friction, leading to bubbling that produces volcanoes
transform fault`
when two plates slide past each other
isostatic leveling
responses of a plate rising or falling on the athenosphere due to changes in density. this relies on the principle of archimedes where the force pushing up an object to be buoyant is equal to the weight of fluid that the object displaces.
active margin
a convergent boundary where an oceanic plate is crashing with a continental plate
narrow continental shelf
passive margin
no crashing between plates
there is no seismic activity
no trenches
there is a wide continental shelf
amplitude of a wave
half of height
wavelength
distance from a peak to a peak
equation for frequency
T= 1/f
wave speed
C= wavelength / time
wave steepness
amplitude / wavelength
what is the path of a water molecule in wave?
one circle
draw a diagram of a wave and draw the velocity vectors
done
what is a wave
a disturbance or vaiation that transfere energy progressively from point to point in a medium
What propagates in a wave?
not the water itself, but the form of waves
crest
highest point on the wave
trough
lowest point on a wave
height of a wave
vertical distance between crest and trough
amplitude
half of height
wavelength
distance between adjacent wave crests
wave period
the time between the arrival of succesive wave crests
wave frequency
the number of waves in a cycling passing a given point at each second
wave phase speed
c = L/ T (wavelength divided by time)
what do waves travel through
sometimes directly through a medium (sound). some will travel along the boundary between two different media (waves on a puddle)
what is needed in order for a wave to occur
a disturbance
a restoringforce
a means for the energy to travel away from the source
what is a restoring force
a force that gives rise to equilibrium in a system. For waves, it is a force that tends to return a sea surface to its original flat state.
what are restoring forces for the ocean
gravity
surface tension
earth's rotation
how does surface tension act as a restoring force
it acts similarly to a trampoline, causing a depression to "snap back"
how does gravity act as a restoring force
Gravity causes a pressure gradient from the top of a wave height to the trough of a wave. Water that is piled up at the crest has more pressure on water molecules, than at the trough. Pressure gradients move from high pressure to low pressure
what kind of energy does a molecule have at the top of a wave
potential
what kind of energy does a water molecul have at the bottom of a wave
kinectic
what causes a wave
a disturbance where the sea surface is displaced
what are examples of a wave disturbance
wind
verical displacement
something that causes a pressure disturbance
the diameter or water molecule orbit circulation is halved how far in the water column?
1/9 of the wavelength
At what depth does a wave orbit become flattened?
half the wavelength

it becomes a surge back and forth
explain wind waves and how they disturb
small variation in wind speed and pressure that occur across a smooth surface causes capillary waves to develop. atmospheric pressure is generated on the faceward side of the wave that essential becomes pushed, while the leeward side there is an a lower pressure. As always, pressure moves from high to low.
Waves between what period have the most energy
0.2 and 30 seconds
what is the equation for wave spped that takes into accound depth and wave length
c = sqrt ( (gL/2pi) * tanh (2pid/L))
What is qualifies as a "deep" wave
d > L/2
what is the approximation for wavespeed of a deep water wave
c = sqrt (gL/2pi)
What qualifies as a "shallow" wave
d < L/20
What is an approximation for wave spped of a shallow wave
c = sqrt (gd)
what is the motion of a shallow water wave
elliptical
why doesn't the ocean look like smooth singular waves moving across the surface?
because of interference
phase velocity
velocity of wave peaks
group velocity
velocity of wave packet
when the phase velocity doesn't equal the group velocity what speed does the wave energy travel at?
the group velocity
in deep water, group velocity =
1/2 phase velocity
in shallow water, group velocity =
phase velocity
what is a rogue wave
a wave that results in the addition of many waves and is extremely large in comparison to the "norm" of waves
what causes waves to break
because the waves become too steep and top starts having a faster velocity than the rest of the wave.

this occurs at H/L = 1/7 or about 120 degrees
what are the wind factors that control wave growth
strength
duration
fetch (distance over which the wind blows unimpeded across the water)
fetch
distance over which the wind blows unimpeded across the water
beaufort scale
on a scale of 0 to 12 it measures the intensity of at sea weather. this is usually a response to the sea by wind forcing
what limits the height of waves in shallow water
water depth
what is a fully developed sea
ocean waves are so energetic that input from the wind = losses due to wave breaking
in the equation for wave phase speed what does L and T stand for?
wavelength = L
period = T
what limits the fetch of wind?
In the N or S direction it is limited by the fact that wind is in bands along the earth, like the tradewinds and the westerlies

Landmasses and reefs alter the travel of a wave
Why are higher waves more common in the pacific
because the atlantic and indian oceans are more narrower and provided a limited fetch
In deep water, are long waves or short waves faster?
long waves
Waves in Oregon originate from where?
Storms in the Gulf of Alaska or Baja California
Explain the presence of kinectic and potential energy in a wave
kinetic energy is due to the motion of water particles in waves

potential energy is due to the changing height of particles throughout that motion
What is the equation for wave energy
E= 1/8 density *g*wave height (H)
Wave power
the rate at which energy is propogated, per unit lenght of a wave crest

P = c*E
How does current effect wave height
When wave motion is opposite of the direction of the current, then wavelength shortens, leading to an increase in wave height.
significant wave height
measure of the average height of the highest one third of all waves within a given area at a specific time
Explain what wave shoaling is
Wave shoaling is the process where wave height changes in response to a change in water depth.

This is best illustrated through a wave coming to shore. As the waves come into shore, they interact with the bottom. The friction of the bottom causes the waves to slow down, leading to a decrease in wavelength. However, energy is conserved, so energy instead is transferred to height.

Eventually, maximum steepness occurs, leading to the top of the wave moving faster than the bottom, causing breaking
Why do waves flow mostly parallel to the shore?
This occurs due to wave refraction. As one portion nears the shore quicker than another point in a wave, it slows down, while the faster points catch up until they are all traveling at the same speed.
What causes a wave to dissipate?
Viscosity between water molecules. (Internal friction)

Friction with other surfaces
In a wave train, how is energy transferred
some is transferred forward to intiate orbital motion in undisturbed water molecules, but the other half of the energy is transferred back to the second wave in the train
wave trains
a group of waves traveling together
What is a result of the energy being transferred in a wave train
the leading wave loses energy, causing it to lose height and eventually dissipate
What is another way to think of the relationship that group velocity is 1/2 of the phase velocity
the speed that a wave train moves at is 1/2 the speed of an individual wave
Why do longer period/wavelength waves arrive before shorter period/wavelength waves at a given locatin?
Because in deep water, waves with longer periods and greater wavelengths contain greater energy and travel faster
in waves that are in a water depth of less than L/20, what controls wave speed
water depth
What way do wave rays bend in shallow water?
towards shallower water
How does refraction affect wave energy
In deep water, a wave has the same amoutn of energy per unit length along the entire wave crest. When the wave is refracted, energy is conserved, and as the length of the wave is increased, the wave height decreases.
What causes the shape of breaking waves
the slope of the beach
Spilling breaker
a wave break that is formed when the sea bottom is almost flat. The wave height reaches a bottom depth about 1.2 times its height and it becomes unstable
Plunging breaker
Have the spectacular curl

Formed on seafloor that is moderately steep.

As the wave approaches the slope, the bottom of the wave is slowed faster than the top, causing the wave crest to curl over
Collapsing breaker
rare waves that occur when the seafloor has a steep slope. What happens is the bottom of the wave slows down so quickly that the leading face collapses before the wave crest can eve break.
Surging breaker
occurs on very steep slopes where waves appear not to break at all
Set down
the gradual shoreward decrease in the mean sea level height
set up
an increase in mean sea level height, found within the surf zone
explain rip currents
Wave breaking causes a build up of water near shore, leading to a pressure gradient from near shore to off shore. This water eventually breaks through the surf, preferrably in an area where wave heights are low. These narrow jets are called "rip currents."
Wave diffraction
when a wave encounters an obstacle it will bend around it
What is a standing wave?
the sum of two waves traveling in opposite directions
node
a place of intersection where waves cancel each other out. the motion is stationary
antinode
place of maximal amplitude, located halfway between each node
In a standing wave, where is the speed the greatest
at the node
in a standing wave, where is the speed zero
at an antinode
seiches
stationary waves in basin modes
what are standing waves important in basins
they can grow to be quite large
Tsunamis are generated from what?
seismic events such as an earthquake or landslide causes a large displacement of water
Are Tsunamis deep water or shallow water waves?
tsunamis are shallow water waves because they have a very long wave length (100 to 200 km) and have large periods (10 to 30 minutes). Because most of the ocean floor is less than 4 km deep, most of the ocean floor is less than one twentieth of the wavelength of a tsunami.

Therefore: c = sqrt (g * D)
What causes a Tsunami to get its incredible size?
As the tsunami enters shallower water, it's wavelength is reduced, but its period is unchanged (like any other wave), leading to an increase in wave height.
internal waves
waves occurring at the boundary of a pynocline: where two distinct different densities meet.
slick
surface visual of an internal wave
What is the speed of internal waves? What does it depend on?
They are usually slow, because the depend upon a difference in the density between upper and lower layers
A slick represents what portion of an internal wave?
the trough of an internal wave
explain the idea of stokes drift
waves are more complex than pure sine waves, which are closed paths (begin and end at same place). Instead the orbits don't quite closed, leading to some forward motion by the object in the path.
Explain stokes drift
That a water particle does not travel in a pure sine wave pattern where it ends up exactly where it began. Instead the orbits aren't closed and result in a slightly forward motion of an object floating on the surface of the water
what are ways that the tide is measured
-tide stations have have a pully with a counterweight
-acoustic sensors
-pressure gaugesq
What are some potential problems with measuring the tide in a tide station
stations are located near river mouths which could cause a change in sea height

there could be wave interference
What causes differences between predicted and observed tides
storm surge --> (set up)

low atmospheric pressure zone (rise in sea water level)
ebb vs flood
flood is the coming in of the tide
ebb is the going out of the tide
What is a tide?
a very long ocean wave

wavelength is about 1/2 of the earth's circumference
diurnal tide
one change in the tide a day
semidiurnal tide
two low and high tides in a tide
mixed tides
have two low and high tides, but at different heights
explain the equilibrium theory of tides
note: oversimplified to explain priniciples

-no continents w/ water at uniform depth
-ignores friction
-assumes instantaneous equilibrium
newtons law of gravitation
f = G x (M1 x M2)/D2

D= distance between two
G = gravitational constant
M1 and M2 are the masses of the objects
How does gravity and centrifugal force affect tides?
The moon and the sun exert a gravitational force, as described by newton's law of gravitation.

Centrifugal forces results from the rotation of two bodies about each other. When two bodies are of unequal weight, their common point of rotation is located closer to the heavier object (in this case, earth (moon) and sun (w/ earth)) The centrifugal force is the force pulled inward to that common point of rotation. In the case of the Earth, everything is unaffected by this gravitational pull except water, which is constantly in motion. This results in a buldge
spring tides
largest tidal range
neap tides
smallest tidal range
how much force does the sun exert on the earth in comparison with the moon?
1/2 of the moon's force
syzygy
when the moon and sun and earth are almost aligned
explain the difference between a spring and neap tide, what is occuring?
During a spring tide, the sun, moon, and earth are aligned. This causes the bulge to be magnified on the earth. As a result, high tides are higher and low tides are lower.

During a neap tide, the moon and sun are 90 degrees apart with respect to the earth, leading to a reduced high tide, and raised low tide.
How often to spring tides occur in a lunar cycle?
1/2 a lunar cycle
how long is a lunar cycle
29.5 days
What depicts whether a point on the Earth will experience a diurnal, semidiurnal, or mixed semidiurnal tide?
It depends upon where the point is located latitudinally with respect to the lunar tidal bulge. A point at the top or bottom of the earth has less distance to travel than a point at the equator of the earth. Therefore, A experiences a smaller portion of the lunar bulge, most likely leading to a diurnal tide pattern
Definition of Centripetal Force
It is the force towards the center that glues an object in a circular path
define centrifugal force
it is an imaginary force that counteracts the centripetal force. It is the force away from the center
Tides explanation in terms of centripetal force
Gravitational force is different for individual points on the earth. This happens because the distance between the moon and a given point on the earth can change. Centripetal force, which in the case of tides is the force towards the moon, is the same at every point on the earth. The discrepancy between these two forces is what causes a pressure gradient which is the "tide-generating force."
Tides explanation in terms of centrifugal force
Centrifugal force, which is opposite to centripetal force, is constant at every point on the Earth, while gravitational force is not. Also, the direction of the moon's gravitational force is always pointing towards the center of the moon. This creates different vector angles for the gravitational force at different places on the Earth. Centrifugal force vectors are all parallel. The resultant force between the centrifugal and gravitational force creates the "tide-generating force."
explain the dispersal of a tide generating force
At the points closest and farthest away from the moon, the centrifugal and gravitational forces are parallel,but in opposite directions. While the forces are the strongest at this point because it is closer to the moon, the cancellation of these two forces makes the net tide generating force small, almost negligable.

However, at points farther away from the moon, the gravitational force and centrifugal force are not in complete alignment. (grav force points towards center of the moon) This reduces cancellation, strengthening the tide generating force.

The result of this process is that water has a net movement towards the points that are the furthest and closest to the moon. This causes bulging at those points.
Why are the tides separated by 12 hrs and 25 minutes?
The moon travels around the earth in 24 hours and 50 minutes. (a lunar day) This is why high tides and low tides will occur at different times each successive day.
What causes two different heights of two daily high tides?
The moon's orbited is tilted with the respect to the Earth's axis by 25 degrees. This causes a point to experience different portions of the lunar tidal bulge as the earth rotates. See figure 12.8 on page 320 of the textbook. Observe point C1. It is located within the bulge, which will experience a high tide, but the point C3, which is another high tide, experiences less of the bulge, causing its high tide to not be a strong.
What depicts whether a point on the Earth will experience a diurnal, semidiurnal, or mixed semidiurnal tide?
It depends upon where the point is located latitudinally with respect to the lunar tidal bulge. A point at the top or bottom of the earth has less distance to travel than a point at the equator of the earth. Therefore, A experiences a smaller portion of the lunar bulge, most likely leading to a diurnal tide pattern.