Waves and Tsunami Notes
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Waves and Tsunami Notes – EOSC 114
1.
Identify key properties of waves
-
1 world ocean
-
5 ocean basins (Indian, Atlantic, Pacific, Arctic, Southern)
-
Major transportation route
-
Linked with the atmosphere, (wind drives the circulation of ocean
water)
Waves = the
mechanical expression of energy
.
-
-
Energy transported by waves is related to the wave height, H (deep
water waves)
-
Waves with great heights transport more energy
-
Waves with great heights have long wavelengths sometimes
2.
Use these properties to determine wave speed and behavior in either
shallow or deep water
-
Wave period = 1/ frequency
-
Deep waves speed = 1.56 X T (period of wavelength)
-
Deep water waves are called disperseive waves because the speed is
related to the wavelength
-
Shallow water wave speed = 3.1
√d (depth of the water)
-
Shallow water speed is non-disperseive bc its wave speed is controlled only by
the depth of the water (waves travel slower at shallower depths)
3.
Explain how waves move matter and energy
-
Permanent winds that blow over the ocean produce surface currents
(transferring both water and energy)
-
Occasional winds that blow over smaller areas produce waves
-
Energy transported by waves is related to the wave height, H (deep
water waves)
-
Waves with great heights transport more energy
4.
Describe the forces that generate waves, eliminate waves, and return the
ocean to a flat, undisturbed surface
-
Wind-generated waves are most common
Restoring force =
the force that causes water to return to its undisturbed state.
-
When wind blows over a calm sea, capillary waves are generated first.
As the wind continues and strengthens, more energy is transferred to
the ocean surface, and the waves grow into those that gravity can only
restore.
5.
Explain the factors that determine the roughness of the sea
-
An assessment of the ocean's conditions or the roughness of the ocean
surface is called the "sea state".
-
Sea state is determined by three factors 1) wind strength/ speed
2) fetch 3) wind duration, the length of time that the wind has been
blowing over the fetch
Fetch = uninterrupted distance or area in the ocean
-
A fetch is said to be developed once it has absorbed the maximum
amount of energy it can contain
-
Waves that have the Fastest speed or longest wavelength leave the
fetch first, waves that leave the last are the shortest and slowest
-
Swells propagate away from the fetch in groups called wave trains
-
The stronger the wind and the longer the wind blows over the largest
of fetch, the greater the maximum wave heights achievable in that
patch of ocean.
-
A qualitative measure of the sea state is given by the Beaufort (Wind
force) Scale
6.
Describe how waves interact; explain constructive and destructive
interference
-
The net movement of the water particles Is zero, it ends up in the
same place
-
Wave base = L (wavelength) / 2
Calculations for this question answer how far one has to go to avoid
being disturbed by the wave
-
Deepwater waves do not feel the bottom bc their wave base are
shallower than the depth of the ocean they are passing through
-
Shallow water waves depth = L/ 20, where waves feel the bottom as
the water particles near the wave base are dragging on the bottom as
they move
Constructive interference occurs when the wave amplitude reinforce eachother,
building a wave with a greater amplitude
Destructive interference occurs when the wave amplitude oppose eachother
resulting in waves of reduced amplitude
-
Rogue waves are the result of constructive interference between two
wave trains, no safety precautions can be taken to prevent death or
destruction due to their unpredictable nature.
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7.
Describe wave refraction, seiche (standing waves in enclosed or semi-
enclosed b
odies), and resonance; how do these affect the coast and
people?
-
Bending or refraction of a wave, allowing it to be nearly parallel to the
shore as it approaches
-
The ultimate effect of wave convergence on headlands and divergence
of the embayment is that headlands shrink (erode) and embayment fill
in
Seiche = a resonant wave in a body of water caused by a disturbance by wind or
seismic activity
-
Can oscillate back and forth across the body of water for some period
of time
8.
Relate wave interference and resonance to marine hazards
9.
Describe how tsunami form and how they are detected
-
Rapid addition of mass into the ocean can cause tsunamis
10.
Explain how a tsunami compares with other ocean waves
-
Not related to tides at all
-
Approach shallow water as fast as rising tide rather than the familiar
wind driven oceanic waves
11.
Discuss why tsunamis come ashore so violently
-
Rivers streams and channels act as conduits for the delivery of energy
within a confined space, therefore internal areas can also feel the
effects of tsunamis
12.
Identify tsunami warning signs, and know how to respond
-
Pacific Tsunami Warning centre (PTWC)
-
Monitor civil and military authorities in the islands and elsewhere in the
Pacific about impending tsunamis
-
Pacific Tsunami Warning and Mitigation System (PTWS) in Hawaii
-
Get to higher ground
-
Regional warning systems Tsunameters and buoys positioned at
strategic locations throughout the worlds oceans
13.
Describe the risks from a tsunami for the coast of British Columbia,
especially one resulting from a megathrust earthquake
-
Tsunami may arrive within 10 minutes of an earthquake, may not have
time to issue a warning
14.
Describe how storm surges are generated
- storm surge us an abrupt buldge of water driven ashore by a hurricane, driven
towards the coast
- it is generated by 2 processes occurring at the same time:
a) hurricane winds pushing water into a large/tall mound called the
wind-driven
surge
; and
b) raising of ocean water (literally suctioned upwards) underneath the eye of storm
because of low air pressure at the ocean surface; this second process produces a
smaller effect. The effect of air pressure is called a
pressure surge
(see figure
below).
15.
Identify where and how the maximum surge occur in a hurricane
-
Occur on the last 1-3 days of
hurricane
-
Happen on coast lines
-
Bulge becomes higher in shallower waters
-
Severity of the storm surge depends on the strength of the storm
generating the surge
16.
Define wave breaking and determine when a wave will break
-
Lesson 1
17.
Explain differences between surging, plunging, and spilling breakers
-
Moderate steep ocean bottoms produce plunging breakers
-
Very steep ocean bottoms produce surging
breakers
-
Flat
ocean bottoms produce spilling breakers
18.
Predict the type of breaking wave that will be found on a given beach
-
As a swell reaches the coast its steepness increases to a point where
the height/ wavelength ration nears a value of 1/7.
-
The ratio of the wave height/ depth approaches a value of ¾
-
The wave crests become unstable and the wave breaks
-
Whitecaps begin to form as the wave turned to surf
-
The waves energy dissipates into the surf zone and transformed into
kinetic energy affecting both the water and land
-
Breaking wave is controlled by the slope of the ocean bottom
-
19.
Describe how coastlines affect waves, and how waves affect coastlines
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-
The location of the coast deoends on global tectonic activity and the
volume of water In the ocean
20.
Compare and contrast the effects of artificial barriers such as groins,
seawalls, and other structures, on coastal processes
-
Groins = trap and retain sediments on the up-drift side
-
Groins interfere with longshore transport of sediments such that
deposition and erosion occurs in unexpected places
-
A jetty is built to protect an inlet or harbour
-
A breakwater is a protective structure built to defend against wave
action and erosion.
-
Breakwater is protected from the erosive action of waves
-
A tether-float breakwater removes energy from waves without
interfering with sediment transport along the shore
-
A seawall reduces the effects of strong waves and to defend the coast
around a town or harbour from erosion, they reflect wave power and
can be sloping verticle or curved
21.
Relate these changes to risks for coastal communities
Extra Notes:
The largest wind-driven waves develop in the Southern Ocean around Antarctica. In
which of the following factors does the Southern Ocean have the
biggest
advantage
over anywhere else in the world?
A) Amount of ice cover over the ocean
B) Wind speeds over the ocean
C) All waves are moving at the same speed
D) Fetch
- southern ocean lacks obstructions therefore, has larger fetches that can generate loads of energy
which is why some of the largest waves are produced there
Significant wave height calculations done by:
a) List all the wave heights observed in descending order (tallest wave to shortest
wave);
b) Select n of the tallest waves, where n is equal to one-third of the number of
waves observed;
c) Calculate the average wave height of your selected waves;
d) This is the significant wave height.
-
Significant wave height is an average number
-
Maximum wave height can be up to twice the significant wave height
Shoaling = as waces pve from the deep ocean towards the coastline and into shallower waters,
their characteristics change.
As waves shoal:
-
All waves except capillary waves slow down when they shoal
-
Wavelengths shorten
-
Orbitals flatten
-
Energy is conserved
-
Wave period remains the same
-
Wave height increases
-
Waves steepen
-
Wave energy is transferred to the water and to the ocean bottom and shore
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