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Hazards Got a New Name: Tsunami
Tsunamis: More Than a Splash
Ellie Goodrich
Geri Trower
Ivan Maurer
Ka’ai Young
Physics 1010
Salt Lake Community College
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Abstract
Tsunamis are a natural force of destruction. What are tsunamis and how do they work?
Most importantly, what effects do tsunamis have? Knowing the tsunamis origins, development
process, hazards, prevention, precautions, and technology advancements enables the ability to
calculate its speed and force behind this natural disaster. Attaining a better understanding of
tsunamis will prepare anyone whose path is crossed by this destructive force. As we continue to
study more about their mechanics can we better understand their make-up?
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Introduction
Tsunamis are one of nature’s most powerful and dangerous forces, yet they are one of
the least understood phenomenon. Tsunamis are unpredictable. Tsunamis are a serious
problem with shorelines and coastal areas are being heavy populated. These monstrous waves
bring tremendous destruction and many health issues with its aftermath. It seems that more
tsunamis have been reported in the news recently, and in fact, there have been more than
there had been in the past 30 years.
Most people look at the ocean but don’t really see it. Imagine if you took the purest
most difficult form of big wave riding—paddling into it with just you, the board, and bare
hands! Waiting for the perfect swell to move in after a major storm, makes it an easy ride as
long as the wind is calm giving you 15 to 30 foot waves.
At times it can even get up to 50 feet. Take that image
and now intensify it by a thousand; you now have
conjured up a portrait of a tsunami. No longer the
perfect wave for thrill seekers, instead a wave of mass
destruction carrying along with it chaos and total
annihilation. Behind this natural behemoth is enough
FIGURE 1-1 Area that covers
Ring of Fire (image found at
pubs.usgs.gov/publications/te
xt/tsunamis.html
force and weight to practically clear everything in its
path. Tsunamis have been recorded in every ocean
throughout the world. However, more than eighty percent of all tsunamis occur within the
Pacific “Ring of Fire” (see Fig. 1-1).
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Origins
Tsunami is derived from a Japanese word meaning, ‘harbor wave’: tsu, which means
harbor, nami, which means wave. It was given this name more than 1000 years ago—a fitting
term since these monstrous waves have brought destruction and death to Japanese harbors
and coastal villages. Tsunamis are often mistaken for ‘tidal waves’. It is important to know that
they’re not tidal waves. Tides are caused by the gravitational force of the moon and sea, while
tsunamis are caused by disturbances.
What is a tsunami? Tsunamis are generally created by sudden events that displace the
sea floor, which then causes the sea to compensate for that displacement of water. Sometimes
it may seem that there will only be one wave but they often travel in multiple increments.
Tsunamis are series of waves, where the most dangerous wave may not be the first one. A
tsunami "wave train" can come in surges five minutes to an hour apart. According to Kusky,
“The cycle may be marked by repeated retreat and advance of the ocean.” Most tsunamis are
generated by earthquakes, volcanic eruptions, asteroids, and landslides. In each of these cases,
it creates a rapidly-moving wall of pure force that may not be visible from the open sea.
Considering that tsunami are created by earthquakes along the trenches of the ocean
floor and convergent plate boundaries; which occur frequently within the Pacific Rim shorelines
is why it’s called, “Ring of Fire.” Seismic sea waves are another term for tsunami because
they’re invocative, by generated earthquakes beneath the ocean.
Tsunami Mechanics
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Throughout history, plate tectonics have
caused terrible earthquakes along many coastlines,
or offshore, that have generated a tsunami.
Convergent zones are the main source of essentially
all tsunamis that have occurred and been recorded.
Picture a bridge breaking in-half, one part goes down
while the other overrides it. However, the boundary
FIGURE 1-2 Tectonic Plates (image found at
science.howstuffworks.com)
between the two parts still sticks together. It’s the same
with the uppermost part of the Earth’s crust. As the two tectonic plates stick together, the
bottom plate buckles the other plate up causing an elastic strain (see Fig. 1-2). Due to the
strength of the buckled plate, it pushes the land out, which than launches the water up above
normal. This sudden reaction to displacement of the sea floor and overlaying water due to this
landside—or earthquake results in a tsunami as its final product.
Tsunami waves gain speed as they move along the seafloor. The extraordinary force
Equations Used to Measure Tsunamis
created by seismic disturbance can generate the
Power =
tsunami's ridiculous speed. We can calculate the
tsunami’s speed by measuring the depth of the water
VELOCITY (v) = √gravity(depth)
= √9.8m(ocean depth)
s²
Speed = distanced covered
Time
at the point of time when it passes by; velocity equals
the square root of the quantity g times D. Where g is
the acceleration due to gravity [9.8m/s squared]
FIGURE 1-3 Measuring Tsunamis (created by Ka’ai)
and D is the depth of the ocean water in meters (see
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Fig. 1-3). They can travel hundreds of miles per hour in the open ocean and crash into the shore
with just as much momentum.
Their ability to maintain speed is directly influenced by the depth of sea water. The
speed combined with the height of the waves causes the great devastation that comes from a
tsunami impact. Wavelength is the distance between the crests which is the highest part of the
wave. Opposite from the crest is trough, which is the lowest part of the wave that measures the
wave heights vertical distance from the crest to the bottom. As for the amplitude of the wave,
it’s one-half of the wave height. They can travel faster in deeper water, although they tend to
move slower in shallower water. Therefore, they are felt at much deeper and greater depths
than normal waves. Definitely unlike the characteristics of a normal wave, the driving energy of
a tsunami moves through the water as opposed to on top of it. Consequently, as the tsunami
moves though deep water we can barely recognize it above the waterline. Typically a tsunami is
no more than 3 feet high until it approaches closer to shore. The friction from the sea floor
from the base of the wave causes the waves exceptional speed to slow down. Once closer to
shore do we recognize its true and deadly form. Once a tsunami is generated, the waves move
in all directions from the origin point. As the waves move along, the waves can split and that’s
how we get the term ‘wave train’ (see Fig 1-4).
FIGURE 1-4 Illustration of tsunami waves (image found at http://kids.britannica.com/elementary/art-87827/A-diagramshows-the-different-elements-of-a-tsunami)
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Tsunamis can be broken down into stages. Beginning with the initiation, the disruption
displaces the water and creates the wave. Stage two being that the wave splits. Splitting occurs
when the wave travels throughout the ocean when parts of the waves move faster than the
others (see Fig. 1-5). After splitting, amplification occurs. This is when the wave gains its size as
it moves up the shore. As the amplitude of the wave increases the wavelength decreases
causing the wave to become steep. Run-up occurs after the wave has amplified; this when the
waves are going from within the ocean and onto land. This is when the impact occurs. And what
sets tsunami waves apart from tidal waves or your typical shore waves.
FIGURE 1-5 Generation of tsunami (image found at oregongeology.org/tsuclearinghouse/faq-tsunami.htm)
Hazards
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Most tsunamis are initiated by earthquakes that occur underwater, but not all of these
earthquakes will produce a tsunami. In order for an earthquake to cause a noticeable tsunami it
must have a magnitude
of at least 6.75 on the
Richter scale. Because
of this, larger tsunamis
only occur on an
average of about 6 per
century with ninety
percent of those
occurring in the Pacific
FIGURE 1-7 Waves Propagate away from origin (image found at
(http://www.pmel.noaa.gov/pubs/outstand/tito2809/tito2809.shtml
Ocean. A very large tsunami can do some serious damage even when it occurs thousands of
miles away from where the earthquake that caused it originated. Although there has never
been one recorded that has gone farther than a mile inland. There is no way to calculate how
many smaller tsunamis occur because their effects are rarely noticeable at all. Types of
tsunamis that are especially dangerous are those that are generated locally. Locally generated
tsunamis have the potential to reach a nearby shore in the span of 10 minutes, which is not
sufficient time for any tsunami warning center to
issue a tsunami warning. Luckily however, nature has
its own warning signs as well. These come in the
form of shaking of the ground caused by the
earthquake that has produced the tsunami, as well
FIGURE 1-6 Tsunami Hazard Sign (image found at
http://pubs.usgs.gov/circ/c1187/)
a
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as unusual ocean changes, such as unusual receding of the ocean, and the sound of loud ocean
roars. Some places that are the most dangerous to be during a tsunami are beaches, bays,
lagoons, and even some river mouths (see Fig. 1-6). Basically the whole coast of California is
exposed to the possibility of a tsunami. Remotely generated tsunamis give ample time for the
local tsunami warning centers to detect the waves and give warning. Remote tsunamis can take
hours to hit the shore.
Wave propagation, or wave movement, is something that can get a little messy due to
the many factors that affect the movement of a tsunami once it has developed (see Fig. 1-7).
Once there is a disruption on the seafloor, the water is displaced and tsunami waves are
formed. Once they are formed they move in all directions away from the origin point.
Some of the health hazards that follow a tsunami range from physical and emotional
distress. Many deaths occur from them as well as other
physical injuries such as broken bones, concussions,
amputations—list goes on and on. The devastation that
comes from these monstrous waves is tremendous;
destruction and death are everywhere you look (see Fig.
FIGURE 1-8 Tsunami aftermath in Banda
Aceh, Sumatra (image found at
http://www.loc.gov/rr/scitech/SciRefGuides/
naturaldisasters.html)
1-8). Many tsunamis’ can occur in third world countries
where poverty is immense. Third world countries tend
to suffer more in times of hardship, and their homeless population will increase dramatically.
Often in these countries more die from the after effects of the tsunami rather than the tsunami
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itself. Trailing behind these monstrosities are disease, hunger, depression, and many other
consequences.
Technology
As mentioned before, the first wave is not always the most dangerous. It isn't until the
second or third waves that it will bring destruction to the shore communities. This is where the
Tsunami warning system comes into play. All coastal regions have their own warning systems
and methods and all are very vital, because although tsunamis like all natural disasters cannot
be prevented, the impact and damage can be limited and reduce through timely warnings and
effective response.
Tsunamis still cannot be predicted.
However, the Tsunami Warning Centers have
developed a system that will note any seismic
changes or any disruption and displacement
of water in our seas. This system is known as
DART, Deep Ocean Assessment and
Reporting of Tsunamis. A DART system is a
buoy sensor system that is deployed in
earthquake prone areas of the ocean floor
(see Fig. 1-9). The sensors on the seafloor
FIGURE 1-9 DART System
(http://www.ndbc.noaa.gov/dart/dart.shtml)
take note of changes in water pressure and seismic pressure then relays that information to a
satellite. It then is sent to the Tsunami warnings centers where they there can assess impact
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time, impact location, wave height, and even predict flood levels and severity. This allows
warnings to be put into place so the communities can reach higher ground before the wave
hits.
Back in 2004, the most devastating Tsunami we have ever seen ravaged the coastal
communities of the Philippines. Back then we only have four DART systems in place and could
not predict the wave height or flood severity. We now have forty-seven DART systems in place
on the seafloor and can predict flood severity and wave height, so we can better warn and take
the necessary precautions to lessen the devastation a tsunami will take.
Prevention
Unfortunately, like all natural disasters a Tsunami cannot be prevented. However, with
today’s technology and the developments in Tsunami prediction and the warning systems, we
can decrease the toll and devastation a Tsunami will take. It is very important that if you live on
the coast you are aware that a Tsunami can hit anywhere along the coast at any time. “The
Indian Ocean Tsunami of 2004 gave rise to levels of loss and grief unprecedented in the history
of natural hazards in the region. Much of the Tsunami impact was due to the lack of public
awareness, effective warning systems, and implication of mitigation measures (National Science
and Technology Council).” It is highly important to be educated on Tsunamis and how your local
warning system works (see Fig. 1-10).
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Although Tsunamis cannot be prevented, there are many ways to mitigate, or reduce,
the damage that is produced. One way, that is sheer common sense, is to not build structures
or communities in Tsunami endangered areas or in areas close to the shore and is below sea
level. Any building built in an area that is prone to Tsunamis should be built on high ground and
away from the shore. Some other
ways are given in a case study from
the University of Washington. One
way is to slow the water flow of a
Tsunami by planting forests, digging
ditches, or creating slopes between
the ocean and the community.
However, the effectiveness of these is
based solely on the power and force
FIGURE 1-10 Image found at
homepages.cae.wisc.edu/~chinwu/CEE514_Coastal_Engineering/2
003_Students_Web/Dan/Tsunami.html
produced by the tsunami.
Another strategy to reduce damage mentioned in the study is to somehow strategically
channel the water to previously designated areas that were built specifically for the situation or
that can withstand major flooding such as ditches or paved roads. Building angled walls and
high rise river dikes can be a major factor in steering the water to those designated safe areas.
A third mitigation strategy that was discussed in this study is to simply build structures strong
enough to withstand the impact of a tsunami, such as walls, water gates, hardened terraces and
parking structures, in-between the shore and your community. If it is decided to construct
buildings in high risk areas it is good to note that “buildings made of concrete, masonry and
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heavy steel frames tend to withstand a tsunami if it is unaccompanied by an earthquake.
Houses made of wood, manufactured houses and light steel frame structures did not fare well.”
Tsunami Mitigation and Prevention
Today, all tsunami affected coastal zones now have sea walls as a protection measure.
Sea walls are manmade structures, mostly built out of concrete, erected on or near a shore line
and are used for absorbing the energy of tsunamis and for protection of the land behind the
wall (See Fig. 1-11). These all vary individually in height and length based upon the most recent
tsunami wave height in that area and aspects
specific to its location which include climate and
coastal position. These sea walls act as a deflector
in that they divert the force and energy of the
water flow and push the water back out to sea.
The seawall is a static feature and being so it will
compete with the dynamic nature of a tsunami
FIGURE 1-11 Example of a Sea Wall (image found at
http://pixgood.com/sea-wall.html)
and impede the impact force and hopefully stop
the tsunami from reaching inland.
There are a couple of disadvantages to sea walls as well, one of them being erosion of
at
the wall over time. As waves break along the seawalls, the force of energy is transmitted
downwards to the bottom of the seawall, causing deterioration and will eventually lead to a
collapse of the wall. Because of this seawalls have to be carefully and frequently preserved.
Another disadvantage is the cost of building sea walls, it is definitely not cheap. The average sea
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wall can cost around ten thousand dollars to build only 80 feet of wall. But if you think about it,
that could be a lot cheaper than having to pay billions of dollars in damage repair.
Conclusion
Just like their land equivalent such as earthquakes, volcanoes and landslides the
underwater disruptions are just as powerful and with the water that is disrupted the wall of
pure force that is created is deadly. It is important for people who live along the coastlines of
the world to understand that tsunamis are not recognizable in the open ocean. It is not until
they reach the shallower waters closer to shore that the waves grow to the walls of water that
do all the damage. However, there are natural warning signs that are detectable. These warning
signs come in the form of shaking ground caused by the earthquakes, as well as unusual
receding of the ocean and loud roars emitting from the ocean itself.
Though people tend to like to live by the
beaches and coast lines, and we have large
communities in these types of places, they’re also
some of the most dangerous places to live. Death
and destruction is what tsunamis are all about and
even though the destruction is inevitable the death
and physical injuries can be kept minimal if people
are educated about the warning systems that have
been put into place. Locally generated tsunamis do
FIGURE 1-12 Warning Steps of tsunamis (image
found at collaborate.coast.noaa.gov)
not allow enough time for any type of warning system to be effective but remotely generated
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tsunamis allow enough time for people to get out of the way of the destructive path as they can
take hours to hit the shorelines (see Fig. 1-12).
Tsunamis still cannot be predicted or prevented but the Tsunami Warning Centers have
developed a system that notes any seismic changes or any disruption and displacement of
water in our oceans. With these warning systems in place, and with public awareness, there is
enough time for people to get out of the way thereby minimizing the death and injuries that
can be caused by these waves of destruction.
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Reference List
Bacher, Kevin. (2005). National Geographic. Tsunami: Killer Wave. [DVD]. United States:
Bacher.
Kusky, Timothy M. (2003). Geological Hazards: A Sourcebook. Westport, CT: Greenwood
Press.
National Science and Technology Council. (2005). Tsunami Risk Reduction: A Framework
For Action. Retrieved from
http://www.sdr.gov/docs/Tsunami%20Risk%20Reduction%20for%20the%20US%20%20A%20Framework%20for%20Action%202005-12-22.pdf
National Oceanic and Atmospheric Administration, NOAA. Tracking Tsunamis. Retrieved
from http://oceantoday.noaa.gov/trackingtsunamis/
National Oceanic and Atmospheric Administration, NOAA (2004, Dec 9). Tsunami
Science: 10 Years Since Sumatra. Retrieved from
https://www.youtube.com/watch?v=ivsNyo52DI8&feature=youtu.be
National Oceanic and Atmospheric Administration, NOAA. Tsunami. Retrieved from
http://www.tsunami.noaa.gov/
Tobin, Harold J. Ph.D. (2011). Oceanography: Exploring Earth’s Final Wilderness.
Chantilly, VA: The Teaching Company.
"Tsunami Mitigation and Prevention." University of Washington, 26 Mar. 2005. Web. 18
Mar. 2015. <washington.edu>.