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28-05-2011, 10:48 PM

“Asian Tsunami“

Introduction:

In this report I will talk about the tsunami. A tsunami can be defined as a series of water waves, which can be produced either by natural or artificial impacts on large water bodies, like oceans. Tsunami involves an irregular deformation of plate boundaries, which causes very large vertical displacements of overlying water. A well known Tsunami Fact is that these have very low amplitudes and large wavelengths while offshore, which makes them harmless at sea. It discovered in the 1950s, that landslides, impact events, and explosive volcanic eruption could trigger larger tsunami, caused by larger displacement of water. A tsunami cannot be predicted as there is no advance warning of approaching waves, however an earthquake centered in oceans may be an indication of a tsunami. Animals have also been found sensitive towards an approaching tsunami, as documented in the case of Lisbon quake, and the 2004 Indian Ocean earthquake. This Indian Ocean earthquake initiated a series of tsunamis, refered as Tsunami 2004 and Tsunami 2005, along the coasts of Indian Ocean, which killed 225000 people in eleven countries. It was an undersea earthquake occurred on 26 December, 2004, with an epicentre off the west coast of Sumatra, Indonesia. It had a magnitude between 9.1 and 9.3, which is the second largest earthquake ever recorded on a seismograph. The aftermaths of Tsunami 2004 were also experienced indirectly through various tsunami videos and tsunami photos, which grieved people throughout the globe. Recently many tsunami-prone countries have implemented various technologies to mitigate onshore damage, while natural methods have also been explored. Tsunami warning systems, including a sensor network and a communications infrastructure, have also been used to detect the waves. Artificial technologies include the use of floodgates, tsunami walls, and channels to redirect incoming water waves. It has been suggested that tree plantations along the stretches of seacoast can provide a cost-effective natural method to mitigate major damages caused by tsunami waves.

Body:

Tsunamiare large, powerfulwater waves caused by sudden displacement of large volume of water in the sea / ocean. Although relatively infrequent, violent volcanic eruptions represent also impulsive disturbances, which can displace a great volume of water and generate extremely destructive tsunami waves in the immediate source area. According to this mechanism, waves may be generated by the sudden displacement of water caused by a volcanic explosion, by a volcano's slope failure, or more likely by a phreatomagmatic explosion and collapse/engulfment of the volcanic magmatic chambers. One of the largest and most destructive tsunamis ever recorded was generated in August 26, 1883 after the explosion and collapse of the volcano of Krakatoa (Krakatau), in Indonesia. This explosion generated waves that reached 135 feet, destroyed coastal towns and villages along the Sunda Strait in XXXX the islands of Java and Sumatra, killing 36, 417 people. It is also believed that the destruction of the Minoan civilization in Greece was caused in 1490 B.C. by the explosion/collapse of the volcano of Santorin in the Aegean Sea.

How Do Earthquakes Generate Tsunamis ?

Earthquake in China, 12 May 2008
Tsunamis can be generated by tectonic earthquakes, which occur due to earth's crustal deformation, and abrupt dynamics of tectonic plates. A geological theory of plate tectonics has been developed to explain the large scale dynamics of the Earth's lithosphere, which sometimes results in tectonic earthquakes. It proposes that Earth's lithosphere is broken up into seven major and many minor plates, called tectonic plates. Tectonic plates or lithospheric plates are large, irregularly shaped slabs of solid rock, consisting of oceanic and continental lithosphere. Plate boundaries at the edge of tectonic plates undergo large deformations due to interaction between two plates, which causes earthquakes. Large volumes of water above the deformed area gets disturbed from its stable equlibrium due to the disturbances caused by these earthquakes. The largely disturbed mass of water strives to gain its original stable equilibrium configuration to minimize system's internal energy. This system includes water mass and earth's surface beneath it, which attracts water to its minimum potential energy position through gravity. This process creates gigantic and massively destructive water waves known as tsunami. Tectonic activities and Tectonic motion have been estimated using various space geodetic technologies such as Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), and Global Positioning System (GPS)

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How do volcanic eruptions generate tsunamis ?

Primarily a tsunami is generated when any natural or artificial force disturbs large volume of water particularly or largely in vertical direction through sea floor. These water waves have very high frequency and very small wavelengths in onshore areas, which causes mass destruction. A submarine or offshore volcanic eruption can produce high magnitude lifts on seafloors, which pushes large water columns upwards to generate tsunami. Submarine volcanoes can be detected by the presence of high rock XXXXXXX and steam above water surface. These submarine volcanoes form high slope pillars over their craters as compared to their on surface counterparts, which is due to the rapid cooling effect of water and buoyancy. The process of tsunami generation in such cases can be understood through the concept of phreatomagmatic eruption. Such an eruption is an explosive interaction between water and magma, which produces fine grained tephra with the emission of magmatic gases and steam. Another considerable fact is the failure of a submarine volcano's slope which results in sudden disturbance of water resulting in tsunami waves.

Where and how frequently are tsunamis generated ?

Tsunami waves are generated in large water bodies like oceans and seas, as these waves consist of large volumes of water disturbed by natural or artificial impacts. However the frequency and location of a tsunami depends on the source cause as various affecting factors may have varying availabilities depending on the location. Factors like submarine volcanic eruption, landslides, and earthquakes have major impacts on generating a tsunami, so these factors also decide the frequency and location of a tsunami. The Pacific Ocean occupies more than one third of the earth's surface and is bounded by areas called the “ring of fire”, which includes mountain chains, underwater trenches, and islands. This area is on the highest earthquake-prone zone, which include the coastal zones of Kamchatka, Japan, the Kuril Islands, and South America. All the regions of world have differing frequencies of tsunami generation with varying intensities of destruction. Destructive tsunamis have occurred in Nicaragua (1992), Indonesia (1992, 1994, 1996), Japan (1993), Philippines (1994), Mexico (1995), Peru (1996, 2001), Papua-New Guinea (1998), Turkey (1999), and Vanuatu (1999) in the last decade. The 2004 Indian Ocean earthquake provoked world's deadliest tsunami which killed about 250000 people.

Tsunami Waves

Tsunami waves are mechanical waves and thus energy transfer is through the phenomenon of compression and rarefaction. These waves move through their source towards the onshore areas due to the additional impact of wind on the surface of water. This phenomenon of water wave movement can be understood as the generation of ripples on water surface when disturbed by any external impact. In a tsunami wave, the whole of water mass moves about 30

meters horizontally to and fro from the impact which caused it. Another up and down motion combined with this to and fro motion causes the wave to travel in an elliptical geometry. A typical tsunami wave can have an amplitude A of 1 meter and a wavelength L of the order of 799.9 kilometers, which can be used to calculate its speed. For the average depth of the Indian Ocean, which is three and a half kilometers, the speed of water waves was calculated as around 650 kilometers per second. Such speeds combined with high associated energy levels explains the destructive capabilities of tsunami waves.
Why Aren't Tsunamis Seen At Sea Or From The Air ?

It is a well known fact that tsunami waves have very low amplitudes and large wavelengths while offshore due to larger volume of surrounding water. A typical offshore tsunami wave can have an amplitude A of 1 meter and a wavelength L of the order of 799.9 kilometers. So the energy associated with these offshore tsunami waves is also very low due to such lower frequencies, or smaller amplitudes. So these waves are difficult to experience and its virtually impossible to see them at sea or from air.

What Are The Factors Of Destruction From Tsunamis ?

Tsunami causes destruction primarily due to the ultrahigh impacts on structures and other assets. The basic factors of destruction include, wave impact, erosion , and inundation. The drag applied by tsunami waves on structures can move them or overturn them. The presence of high salt concentration in tsunami waves causes corrosion of XXXXllic bodies, which decreases their life ultimately leading to failure. As tsunami causes large scale structural destruction, the floating debris so formed poses serious threat to other structures, or floating vessels. Besides the primary destruction, secondary destruction may include fire hazards, and water pollution. Fire hazards may be caused by severed electricity transmission lines, while damaged oil tankers may contribute a serious threat to water quality.

What Are Some Of The Largest Historical Tsunamis ?

Destructive tsunamis have occurred in all of the world's oceans and seas. In the second half of the 20th Century, Pacific-wide, destructive tsunamis occurred in 1946, 1952, 1957, 1960, and 1964. Many more tsunamis occurred in inland seas around the periphery of the Pacific Ocean, which were extremely destructive locally and claimed thousands of lives. Such localized tsunamis occurred in 1975, 1983, 1985, 1992, 1993, 1995, 1998, 1999 and 2001.

1st April, 1946, Aleutian Earthquake and Tsunami
The Aleutian Islands Earthquake occurred near Unimak Island in Alaska's Aleutian Island Chain and was followed by a Pacific-wide tsunami. This earthquake had a magnitude of 7.8 on the Richter scale, with its epicenter at 52.8 degree N,

163.5 degree W, and focal depth of 25 km. A gigantic wave of 35 meters destroyed completely the U.S. Coast Guard's Scotch Cap lighthouse on Unimak and killed all five of its occupants. The lighthouse was a steel-reinforced concrete structure standing about 30 meters above sea level. The tsunami caused 165 casualties and about 26 million dollar in damages. The tsunami is known as the April Fools Day Tsunami in Hawaii as people took the tsunami warning as an April Fool prank.
The 4 November, 1952, Kamchatka Earthquake and Tsunami
A strong earthquake (magnitude 8.2) off the coast of Kamchatka Peninsula generated a great destructive Pacific-wide tsunami. Its waves struck the Kamchatka Peninsula, the Kuril Islands and other areas of Russia's Far East, causing considerable damage and loss of life. The tsunami was widely observed and recorded in Japan, but there was no loss of life or damage there. There was considerable damage in the Hawaiian Islands and some damage in Peru and Chile. The tsunami was recorded or observed throughout the islands of the Pacific. In New Zealand waves reached height of 1m, and in Alaska, in the Aleutian Islands and in California waves of up to 1.4 meters were observed. The largest waves outside the generating area were observed in the Hawaiian Islands. Fortunately, no human lives were lost in Hawaii from this tsunami, but damages were extensive, ranging from $800,000- $1,000,000. In the Hawaiian island chain, the tsunami waves destroyed boats and piers, knocked down telephone lines, and caused extensive beach erosion.
The north shore of the Island of Oahu experienced higher waves of up to 4.5 meters. On the south shore of the island, tsunamis waves were powerful enough to throw a cement barge in the Honolulu Harbor into a freighter. The island of Hawaii experienced drag up to 6.1 meters. In Hilo, a small bridge connecting Coconut Island to the shore was destroyed by one of the tsunami waves lifting it off its foundation, then smashing it down. The effects of the tsunami in the generating area in Kamchatka, varied significantly. From Kamchatka Peninsula to Kronotsky Peninsula, the wave heights ranged from 0 to 5 meters. From Kronotsky Peninsula to Cape Shipursky the heights ranged from 4-13 meters. The highest wave of 13 meters was the third as observed at Olga Bay, where it caused considerable damage. Travel time of the first tsunami wave to Olga Bay was approximately 42 minutes after the earthquake. From Cape Shipursky to Cape Povorotny, the tsunami waves ranged from 1 to 10 meters and caused considerable loss of life and damage. At Avachinskaia Bay the tsunami height was 1.2 meters and its travel time was about 30 minutes. From Cape Povorotny to Cape Lopatkka the waves ranged from 5 to 15 meters. At Khodutka Bay a cutter was thrown 500 meters back from shore. On the West coast of Kamchatka Peninsula, the maximum tsunami run up at Ozernoe was 5 meters. At Alaid Island of the Kuril Island group, run up was 1.5 meters, while at Shumshu Island it ranged from 7-9 meters. At Paramushir Island, the waves ranged from 4-18.4 meters. At Severo - Kurilsk on Paramushir Island, the second wave was the highest reaching maximum run up of 15 meters. It destroyed most of the town and caused considerable loss of life. At Onekotan Island tsunami run up was 9 meters, while at Shiashkoton Island it was 8 meters and at Iturup Island 2.5 meters. Waves of up to 2 meters were observed at the Komandorsk Islands and at Okhotsk. At Sakhalin - Korsakov a 1-meter tsunami wave was observed.

The 9 March, 1957, Aleutian Earthquake and Tsunami
On March 9, 1957, an 8.3 magnitude earthquake occurred south of the Andreanof Islands, in the Aleutian Islands of Alaska. It happened in the same general area as that of April 1, 1946, and generated a Pacific-wide tsunami. Although no lives were lost, there was massive destruction of property in the Hawaiian Islands, with damage estimated at approximately $5 million. The waves were particularly high on the north shore of the island of Kauai where they reached a maximum height of 16 meters, flooding the highway and destroying houses and bridges. This was twice the height of the 1946 tsunami. At Hilo, Hawaii, the tsunami run up reached 3.9 m and there was damage to numerous buildings along the waterfront. Within Hilo Bay, Coconut Island was covered by 1 m of water and the bridge connecting it to the shore, as in 1952, was again destroyed.
The 22 May, 1960, Chilean Earthquake and Tsunami
The largest earthquake ( magnitude 9.5 on moment magnitude scale) of the 20th century occurred on May 22, 1960, off the coast of south central Chile. It generated a Pacific-wide tsunami, which was destructive locally in Chile and throughout the Pacific Ocean. The tsunami killed an estimated 2,300 people in Chile. There was tremendous loss of life and property in the Hawaiian Islands, in Japan and elsewhere in the Pacific. Destructive waves in Hilo, Hawaii, destroyed the waterfront and killed 61 people. Total damage was estimated at more than $500 million (1960 dollars).
The 27 March, 1960, Great Alaska Earthquake and Tsunami
This earthquake is also known as the Good Friday earthquake as it happened on the day of Good Friday at 5:36 P.M. AST (03:36 3/27 UTC), and had a moment magnitude of 9.2 and was 8.4 on Richter scale. It was the most powerful earthquake ever recorded in the U.S. and North America. The epicenter of the earthquake was 61.05, -147.48, 20 km north of Prince William Sound, 125 km (78 miles) east of Anchorage and 64 km (40 miles) west of Valdez. The powerful earthquake caused some parts of Alaska to be liquefied, causing great damage to property and leading to landslides. The earthquake caused areas to be lifted by 15 m (50 feet) in certain areas, while many other areas subsided greatly. In addition to many local tsunamis generated within the Prince William Sound, vertical crustal displacements averaging 1.8 m (6 ft.) over an area of about 300,000 square kilometers (115,000 square miles) extending in the Gulf of Alaska's continental XXXXf, generated a Pacific-wide tsunamis. Its waves were very destructive in southeastern Alaska, in Vancouver Island (British Columbia), and in the U.S. States of Washington, California and Hawaii. The tsunami killed more than 120 people and caused more than $106 million in damages, making it the costliest ever to strike the Western United States and Canada. Five of Alaska's seven largest communities were devastated by the combination of earthquake and tsunami wave damage. Alaska's fishing industry and most seaport facilities were virtually destroyed. Tsunami waves at Kodiak Island washed away a total of 158 houses and buildings within two blocks of the waterfront. Fishing boats were carried hundreds of meters inland. The 1964 tsunami waves caused also extensive damage in Vancouver Island (British Columbia), and in the states of Washington, California and Hawaii, in the U.S.. The waves affected the entire California coastline, but were particularly high from Crescent City to Monterey ranging from 2.1 - 6.3 meters (7-21 feet). California was hit hardest, where waves reaching as much as 6 meters (20-21 feet) destroyed half of the waterfront business district. At Santa Cruz Harbor, the tsunami waves reached as high as 3.3 meters (11 feet) causing some damage. There was extensive damage in San Francisco Bay, the marinas in Marin County and at the Noyo, Los Angeles and Long Beach harbors. Estimated losses in California were between $1,500,000 and $2,375,000 (1964 dollars), while at Crescent City tsunami damage was estimated at $7,414,000.

The story of one of the survivors of the tsunami
Erica Wales, a Peace Corps volunteer in the village of Salesatele, said the earthquake woke her up early yesterday morning.The 23-year-old, who has lived in Samoa since June last year and works as a marine protection officer with the Peace Corps, said she was about 15 metres from the beach when the waves hit. She is blogging from Samoa and provides her story:

I’m lucky to be alive

I’m sure most of you have heard about the earthquake and tsunami that hit Samoa by now and am wondering how I’m doing. Well, here’s the story:

I was sleeping when the 8.0 earthquake hit. My house started shaking and things were falling off XXXXves. Books fell down, the phone mounted on my wall fell down, cans of food fell…I’m smart enough to know when things start falling it is probably wise to get out. So grabbed my phone and left my room. The shaking lasted a long time too, at least a minute. I texted a good friend here with the message of “shit that was big” when it was over. She agreed. About that time I got a call from the Peace Corps medical officer that I should probably move inland because the possibility of a tsunami. So I grabbed an ie and left.

I was walking on the road which parallels the beach when I noticed something wasn’t right. I could see structures like rocks and coral which I have never seen above water, not even at the lowest of low tides. This didn’t bode well. Then I noticed the really odd wave action, something just wasn’t right. I had just turned the corner of the road and was now headed inland, versus parallel to the beach as I had been just one minute before, when the waves hit the beach and surged up the road. At this point I started running, as did my village. As I was running I could hear the water surging up the river, tearing trees down.

I got up to the main road where most everyone was. The matai were directing everyone to head to Siuniu, the village inland. I could see the look of panic and worry as parents asked where their kids were, for they were headed to the primary school which is near me. The matai were organized and knew where to direct the parents to in order to find their kids. I went up to Siuniu and waited with my village. At this point we were getting reports of a school in Poutasi (a few villages to the west) collapsing and killing three kids. Everyone was on phones, calling relatives and friends in neighboring villages, trying to find out what was going on. Reports came that 50 people in Poutasi were dead, buried in the sand. A boy in neighboring Salani died. And 15 in Aleipata were dead. As far as I know at this point, no one in my village died. We are lucky.

Then I got a report that my house and another were destroyed. I wanted to go and see if this was true, but I knew to stay. I waited a few hours then went to see what the damage was. Sure enough, my house was flattened. The tsunami ripped the house from its foundation and deposited it 10 feet in front of the house, collapsed beyond repair. I could see all of my stuff waterlogged and muddy. I’m not sure what can be salvaged. I’m going back tomorrow to find out what I can still use, but I know most things will be trashed.

While that is unfortunate, at least it was just my house and not my home. The other family I feel bad for because it was their home. I had stuff there which will be expensive to replace, but it wasn’t everything in the world I owned, just everything I Samoa I owned. Most of my stuff is still back in the US. I feel bad for the other family who truly lost everything. I feel really bad about the three computers I had in my house for the school. I don’t think those will be salvaged, but another Peace Corps Volunteer already told me she would donate two to my school, so I’m happy about that. I also am upset that I don’t know where my dog is. I saw her after the earthquake, and then don’t know where she went. I hope she is ok. Animals are smarter than humans in many ways, so she probably left before I did, but I’m still worried. I hope I find her.

The Peace Corps Office came out and drove me to Apia. I could see the damage in the villages as I passed. Poutasi looks pretty bad; boats are inland, houses devastated, and the school collapsed. Their village is pretty flat on the seaward side, so the wave did quite a bit of damage. The district hospital there looked like it was spared, might have water damage though. As we were driving over Cross Island Road, many cars were headed south to help clean up and try to find their family.

Once in Apia, small aftershocks could still be felt throughout the day. Around 5:30 pm the tsunami sirens went off. Everyone headed up the mountains carrying what they could. It turned out to be a false alarm, but better safe than sorry. Most businesses were closed as people went to help.

Report is over 80 here are dead. If you want to help,

I want to say thank you to all my fellow PCVs. I don’t think my phone was quite for five minutes yesterday morning. Everyone wanted to see if I was ok; thanks, makes me feel loved. When I got to Apia, a bunch of people offered up their house and everyone wanted to know what they could do to help. I appreciate the support guys. You guys are awesome! Also to everyone who posted on facebook and sent me e-mails, thanks for your support as well. And finally to Teuila; I was awake after the earthquake but not enough awake to be thinking about a tsunami. If she hadn’t called right after the quake stopped, I probably would have been at my house. If I had left my house just a minute later…well, yeah.

I gave a written eyewitness account to Sydney Morning Herald and a phone interview to NY Daily News. Here’s the link for the NY article: American Samoa hit by tsunami after underwater 8.3 earthquake; warning issued for Hawaii (http://www.nydailynews.com/news/world/2009/09/29/2009-09-29_tsunami_hits_american_samoa_.html)

And the Sydney article: Tsunami In Samoa | "I Could Hear Waters Rushing Up" (http://www.smh.com.au/environment/i-could-hear-the-waters-rushing-up-and-tearing-trees-down-20090930-gcay.html)

So that is all I know for now. I’m off to buy some new clothes because I have the clothes on my back and one spare. I’ll keep you posted on what goes on.
Labels: Erica Wales

Ending :
Locally generated tsunami may reach a nearby shore in less than ten minutes due to their high speeds. There is not sufficient time for the Pacific Tsunami Warning Center or for local authorities to issue a warning. For people living near the coast, the shaking of the ground is the only warning that a tsunami may be imminent.

References and sources

1- Tsunami, Tsunami Information, tsunami story , Tsunami Hazard (http://www.mapsofworld.com/tsunami/)
2- http://www.tsunami.noaa.gov/tsunami_story.html
3- تسونامي إندونيسيا (http://www.islammemo.cc/vedio-images/vedio/2010/10/27/109767.html)
4- StoryTsunami - Home Page (http://www.storytsunami.org/)
5- TSUNAMI SURVIVOR STORIES (http://phukettsunami.blogspot.com/search/label/Erica%20Wales)

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