Tsunamis: History, Causes, and Characteristics 1
Tsunamis
History, Causes, and Characteristics
Peter Beilfus, Brian Walker, Taylor Goodsell, Jordan Gardner
Salt Lake Community College
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Abstract
This document discusses various aspects of the natural disasters Tsunamis. Beginning
with a brief history of tsunamis and progressing into the causes of this devastating force of
nature. Concluding with the characteristic and physics involved with tsunamis. The history
describes the Japanese word tsunami, and focuses on early records of the massive tidal waves.
These records include specific events to demonstrate the power of tsunamis and the
devastation they can cause. It also focuses on the progress humans have made in detecting
and preparing for tsunamis. The causes were found to be earthquakes, landslides and volcanic
eruptions that take place in deep ocean. Focusing on the formation of waves and their
interaction with the land this section overlaps with the characteristic of tsunamis. We were
able to learn how exactly the sea rises due to the tops of waves moving faster than the bottoms
because of the land slowing the wave. This section also discusses wavelengths and speeds
produced by tsunamis along with various other physics related subject matter such as
amplitude and frequency. Importantly we also distinguishing the difference between waves
from a tsunami and those caused by wind and tidal changes.
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History of Tsunamis
Originating from the Japanese word tswnami, the word tsunami can be translated to mean
harbor wave or tidal wave, which means to have large amounts of water displaced. It seems
fitting to have the origin of the name come from the Japanese language because of the large
number of tsunamis that occur on the coasts of Japan.
Recordings of tsunamis date all the way back to 426 B.C. by Thucydides, a Greek
historian. Thucydides was also the first to presume that earthquakes were most likely the cause
of tsunamis. He was also the first to make the connection that tsunamis are like unto
subterranean earthquakes.
Since then, not only have scientists learned the true causes of tsunamis, they are also
making advances towards predicting exactly when a tsunami will hit, and with how much
magnitude by using the recordings from previous events where tsunamis took place. So, looking
to the past is a critical part of understanding something as unpredictable as Mother Nature. While
tsunamis will most likely never be preventable, by using the tools scientist have created we are
better able to predict when and where tsunamis will reoccur so that in the future, the devastation
tsunamis cause will not happen again. Below is a picture of a tsunami warning buoy developed
by NOAA.
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While there have been multiple tsunamis that took many lives, the largest tsunami
recorded in modern times only claimed the lives of two men. On July 9th 1958, Lituya Bay,
Alaska, a landslide caused by an 8.3 magnitude earthquake triggered a tsunami where waves
reached approximately 1,720 feet. However, since that region is so isolated, only two the
fisherman who were killed were caught in the eye of the storm.
That same shifting in the earth’s crust however, can be much more deadly when humans
get in the way. Nearly six years ago on December 26th, a magnitude between 9.1 and 9.3 caused
a shift in the ocean floor in Indonesia killing an estimated 230,000 people. However, seeing as
how high the magnitudes of this tsunami were, countries as far as Nova Scotia and Peru
experienced the waves from what was later named ‘The 2004 Indian Ocean Tsunami’ , or
“Sumatra-Andaman”. However, Dr Eddie Bernard, the Director of the NOAA laboratory, called
it “The world’s most devastating tsunami in recorded history.”
Picture one shows the Tsunami crashing into the city while picture two shoes where the tsunami
originated and what places it affected and with how much magnitude.
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History has shown us that while the magnitude of the shifting in the earth’s plates plays a
crucial part in determining the size of a tsunami however, just because a tsunami is high on the
rictor scale, doesn’t necessarily mean that large numbers of lives will be lost. Looking back in
time shows us that a more accurate way of determining the number of lives that a tsunami will
take is to determine how densely populated the area being affected is.
Volcanic eruptions are also known to cause thousands of deaths. When the Krakatoa
volcano in the Indonesian Islands of western Java and southern Sumatra erupted, a tsunami was
triggered that killed approximately 36,000. In fact, the waves caused by the massive eruption
were so large they were able to push blocks of coral as large as 600 tons onto shore. Knowing
that some tsunamis are capable of doing such large amounts of work, it is not surprising that in
the last century, there were twenty-six tsunamis that killed over two-hundred people or more.
Causes
Tsunamis devastate many regions every year, causing mass destruction and claiming
hundreds even thousands of lives. What causes this unstoppable force of nature though?
Tsunamis start on or near the ocean floor in what’s called the subduction zone. This is an area
where an oceanic plate is being forced down into the Earth’s Mantle by tectonic forces. At
times this causes an enormous amount of friction and prevents the slow steady rate at which
the plate would normally move. Instead it essentially becomes stuck. While stuck, the plates
continue to assert force on one another and energy accumulates. Much like the energy stored
in a compressed spring. When the energy becomes too much the plate violently snaps back
into an unrestrained position, causing an underwater earthquake and a tsunami. A tsunami is a
mechanical wave, meaning that it requires a medium to transfer its energy. That medium is the
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water which takes the energy created by an earthquake and transfers that into multiple waves.
Those waves transfer the energy from the water to the shoreline where the energy is dispersed
causing immense damage.
When the oceanic plate snaps into an unrestrained position a massive amount of water
is vertically displaced. Once these water molecules are disturbed they transfer energy to other
molecules until a wave is created. While the Tsunami is in deep water the waves is unnoticed,
generally waves in the deep ocean are no more than a foot high and can travel at speeds up to
500 miles per hour. Once the waves get close to land they begin to interact with that land. As
physics tells us as long as no force interferes energy will remain constant, but as the wave
makes contact with land it, the land causes a velocity decrease; the top of the waves are
moving faster than the bottom of the waves which causes a dramatic rise in the sea. On
average the sea only rises 10 feet but there are cases of the sea surging 100 feet. As the front
of the wave slows all the mass further out to sea catches up and build a larger wave. Waves
from a tsunami can make land fall more than an hour apart. Often time’s tsunamis are not a
series of waves they can simply be made up of a rapidly rising sea that can flood more than
1000 feet inland.
Characteristics of a Tsunami
Physical characteristics of waves.
A tsunami is a type of wave. As such, it shares its basic physical characteristics with
other types of waves. These characteristics are:
1. Wavelength – the distance between two identical points on a wave.
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2. Wave height – the distance between the trough, or lowest point of the wave, and the
peak, or the highest point of the wave.
3. Wave amplitude – the height of the wave above the still-water line, generally equal to
½ the wave height.
4. Wave frequency, or period – the amount of time it takes for one full wavelength to
pass a stationary point.
5. Wave velocity – The speed of the wave, equal to the wavelength divided by the
frequency, or period. This is expressed as V = λ/P.
What makes a tsunami different than a common ocean wave?
A normal ocean wave is caused by wind on the surface of the water, so its energy moves
on the surface of the water, whereas a tsunami can be caused by various disturbances beneath the
surface of the water, such as an earthquake or a landslide, so the energy of a tsunami moves
through the water. This is the beginning of many differences in the characteristics of a tsunami
when compared to a normal ocean wave.
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Normal ocean waves have wavelengths of about 100 meters. The wavelength of a
tsunami is much larger, normally measured in kilometers, with wavelengths up to 500 kilometers
on record.
The wave height and amplitude of a tsunami depend on the depth of the water through
which it is traveling.
A normal ocean wave has a frequency or period of five to twenty seconds, with a
wavelength of 100 to 200 meters. Tsunamis have been reported to have a period between ten
minutes and two hours, with a wavelength commonly around 500 kilometers.
The velocities of the two types of waves are also very different. Common waves
generally travel with a velocity of around 8 to 100 km/h. Tsunami, however, can travel up to
around 800 to 950 km/h in open water.
Tsunamis are characterized as shallow-water waves. This characterization is given to a
wave when its ratio of water depth to wavelength is very small. The velocity of a shallow-water
wave is also expressed as being equal to the square root of the product of the acceleration of
gravity and the depth of the water. ( 𝑉 = √𝑔 ∗ 𝑑 )
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The rate at which a wave loses energy as it travels is inversely related to its wavelength
(Energy loss ~ 1/wavelength). Since normal ocean waves have a relatively small wavelength,
they lose energy much more quickly than a tsunami, since the wavelength of a tsunami is much
larger. Consequently, a tsunami in water about 6100 meters deep can travel around 890 km/h,
allowing it to cross the Pacific Ocean in less than a day.
It is when a tsunami reaches shore that the differences between it and a normal ocean
wave become destructive. Since its velocity depends on the depth of the water, it slows down as
the water approaching shore becomes more and more shallow, and as the decrease in water depth
compresses the energy of the tsunami. However, the change of total energy of the tsunami
remains the same. The period also remains the same, forcing more water between each wave
crest. This is called shoaling, and causes the height of the wave to increase.
When the tsunami reaches shore, it can manifest itself in more than one way. If the trough
or low point of the tsunami is the first part to reach the shore, it causes a drawdown, which
makes it appear as though the sea level has dropped. If the crest or high point of the tsunami
reaches shore first, there is an immediate run-up, bringing the level of the sea above that which is
normal. Most run-ups can get as high as 30 meters, and the inundation of water can travel a few
hundred meters inland. The level of run-up as well as how far inland the water is pushed varies
by the shape of the coast line.
After the first wave of the tsunami hits, washing debris and anyone unfortunate enough to
be caught in it back out to sea, the remaining crests of the wave will also reach shore. Depending
on the wavelength and the velocity of the tsunami, this can take anywhere between a few
minutes and several hours to complete its course. The first wave is also not always the most
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destructive of the series of waves, and subsequent waves have been shown to actually be larger
than the first. In many cases, the second or third crest was shown to be the largest.
It is very difficult to predict the time, location and magnitude of a tsunami. However,
there are signs that can greatly impact your safety. For one, drawbacks are important to
recognize. If you see the water along the shore receding, it is a good sign that a tsunami may hit
that beach. A more accurate way to detect a tsunami is used by geologists and oceanographers.
This method takes place out at sea involving a beacon attached to a buoy and lowered to a depth
from sea level. This beacon reports water pressure and density along certain water columns at
certain places at sea. If, for example, the water gets displaced and a larger than normal tide
occurs, the beacon will report a sudden change in pressure and depth. The pressure will tell how
large the tsunami is, how far apart the waves are, and in which direction it is heading. However,
even if they get an accurate reading from these beacons, it does not mean the tsunami will reach
the shore. If there is a reading and people feel their lives are at risk they will start an evacuation
process. The most accurate way to find out where a tsunami is and how big it will become is to
find the exact magnitude and location of where the underwater movement occurred. Whether it
be an explosion or an earthquake, all the more information is helpful when determining the
outcome of the tsunami.
There are certain cities around the world that tsunamis have hit multiple times. These
cities are more vulnerable to tsunamis due to their geographic locations. Countries like Japan,
Indonesia, and South Africa are prone to tsunamis. Some of these countries have evacuation
routes and methods to relieve stress in threatening times. Furthermore, in some cities they have
built walls and barricades to try and relieve some of the pressures from the tsunamis. However,
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a big enough tsunami will crush the wall or go right over it taking whoever, and whatever is in its
path.
What are Tsunamis are capable of?
Tsunamis are capable of wiping out complete cities. Also, there are predictions or
prophesies that if a meteor hit the ocean it would create a tsunami to wipe the earth over and over
again. Depending of the size of the meteor this is theoretically true. There have been 26
tsunamis within the last 100 years which have killed more than 200 people. There have been
more tsunamis that date back longer than 100 years ago that have been much more severe;
including, one in 1868 northern Chile 25,000 people were killed.
Tsunamis are capable to become however large they can due to however much water is
displaced in one instance. It is unlikely that a tsunami will occur, but if it happens we need to be
prepared for it. Tsunamis cannot be completely prevented only weakened.
Conclusion
Tsunamis are a series of waves caused by a disturbance of the water in any large body of
water. Tsunamis are usually caused by under water land movement or earthquakes. How big a
Tsunami is depends on the initial reaction in which started the process. However much water
was displaced starts the tsunami and determines how big it will become. As a tsunami
approaches shore, the shore composition affects the magnitude of the tsunami as well. Tsunamis
can travel very fast and may happen over long periods of time.
Tsunamis can be predicted however it is very difficult to be accurate. Researches and
scientists rely on beacons that make tsunami prediction easier. In order to predict a tsunami
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researchers gain information about sea depth, pressure, and height of water columns. If they get
a reading from this information devastation may be prevented. The direction and magnitude of
the tsunami is more difficult to accurately predict rather than if there is one actually coming.
There have been many steps in some countries regarding tsunami research and tsunami
protection. The more our world knows about tsunamis the fewer losses we will have to live
through.
Tsunamis have taken many lives and have created thousands of dollars in damage.
Precautions must be taken in order to lessen the damage in the future. Tsunamis are very
powerful and should not be taken lightly by anyone. Please take the time to learn about the
threats in your area regarding tsunamis. Do what it takes to protect yourself and your loved
ones.
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Works Cited
(n.d.). Retrieved October 2010, from tulane.edu:
http://www.tulane.edu/~sanelson/geol204/tsunami.htm
(n.d.). Retrieved October 2010, from wepapers.com:
http://www.wepapers.com/Papers/109431/Physics_of__Tsunami.ppt
(n.d.). Retrieved October 2010, from important.ca:
http://www.important.ca/tsunami_characteristics.html
(n.d.). Retrieved October 2010, from ess.washington.edu:
http://www.ess.washington.edu/tsunami/images/tsunami.pdf
Retrieved October 2010 from geology.com:
http://www.geology.com/articles/tsunami-geology.shtml
Retrieved October 2010 form nativeaccess.com
http://www.nativeaccess.com/teachers/tsunamiwkstsm.pdf
Retrieved October 2010 from Nationalgeographic.com
http://news.Nationalgeographic.com/news
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