TSUNAMI

By – Mansvini Misra, X-B

1) What is Tsunami?2) Why is it important to study about Tsunami?3) Causes of Tsunami4) Movement of Tsunami5) Life of a Tsunami6) Tsunami Watch and Warning7) Tsunami Precautions – Safety tips8) Impact of Tsunamis on Human Life9) World’s Deadliest Tsunamis10) The Indian Ocean Tsunami11) Countries affected by The Indian Ocean Tsunami12) Indian Ocean Tsunami in India13) Special Thanks to the Sources used in this Project

INDEX

What is Tsunami?

A tsunami is a series of ocean waves that are generated by large movements or other disturbances on the ocean's floor. Such disturbances include volcanic eruptions, landslides and underwater explosions, but earthquakes are the most common cause. Tsunamis can occur close to the shore or travel thousands of miles if the disturbance occurs in the deep ocean. The word Tsunami is derived from a Japanese word translating into “harbor waves”.

Why is it important to study about Tsunami?

Tsunamis are important to study because they are natural hazard that can occur at any time in coastal areas around the world. In an effort to gain a more complete understanding of tsunamis and generate stronger warning systems, there are monitors throughout the world's oceans to measure wave height and potential underwater disturbances. The Tsunami Warning System in the Pacific Ocean is one of the largest monitoring systems in the world and it is made up of 26 different countries and a series of monitors placed throughout the Pacific. The Pacific Tsunami Warning Center (PTWC) in Honolulu, Hawaii collects and processes data gathered from these monitors and provides warnings throughout the Pacific Basin.

Causes of Tsunami

Tsunamis are also called a seismic sea waves because they are most commonly caused by earthquakes. Because tsunamis are caused mainly by earthquakes, they are most common in the Pacific Ocean's Ring of Fire - the margins of the Pacific with many plate tectonic boundaries and faults that are capable of producing large earthquakes and volcanic eruptions.

In order for an earthquake to cause a tsunami, it must occur below the ocean's surface or near the ocean and be a magnitude large enough to cause disturbances on the sea floor. Once the earthquake or other underwater disturbance occurs, the water surrounding the disturbance is displaced and radiates away from the initial source of the disturbance (i.e. the epicenter in an earthquake) in a series of fast moving waves.

Not all earthquakes or underwater disturbances cause tsunamis - they must be large enough to move a significant amount of material. In addition, in the case of an earthquake, its magnitude, depth, water depth and the speed at which the material moves all factor into whether or not a tsunami is generated.

Movement of Tsunami

Once a tsunami is generated, it can travel thousands of miles at speeds of up to 500 miles per hour (805 km per hour). If a tsunami is generated in the deep ocean, the waves radiate out from the source of the disturbance and move toward land on all sides. These waves usually have a large wavelength and a short wave height so they are not easily recognized by the human eye in these regions.

As the tsunami moves toward shore and the ocean's depth decreases, its speed slows quickly and the waves begin to grow in height as the wavelength decreases .This is called amplification and it is when the tsunami is the most visible. As the tsunami reaches the shore, the trough of the wave hits first which appears as a very low tide. This is a warning that a tsunami is imminent. Following the trough, the peak of the tsunami comes ashore. The waves hit the land like a strong, fast tide, instead of a giant wave. Giant waves only occur if the tsunami is very large. This is called runup and it is when the most flooding and damage from the tsunami occurs as the waters often travel farther inland than normal waves would.

Life of a TsunamiPanel 1—Initiation: Earthquakes are commonly associated with ground shaking that is a result of elastic waves traveling through the solid earth.However, near the source of submarine earthquakes, the seafloor is "permanently" uplifted and down-dropped, pushing the entire water column up and down. The potential energy that results from pushing water above mean sea level is then transferred to horizontal propagation of the tsunami wave (kinetic energy). For the case shown above, the earthquake rupture occurred at the base of the continental slope in relatively deep water. Situations can also arise where the earthquake rupture occurs beneath the continental shelf in much shallower water.Note: In the figure, the waves are greatly exaggerated compared to water depth. In the open ocean, the waves are at most several meters high spread over many tens to hundreds of kilometers in length.

Panel 2—Split: Within several minutes of the earthquake, the initial tsunami (Panel 1) is split into a tsunami that travels out to the deep ocean (distant tsunami) and another tsunami that travels towards the nearby coast (local tsunami). The height above mean sea level of the two oppositely traveling tsunamis is approximately half that of the original tsunami (Panel 1). (This is somewhat modified in three dimensions, but the same idea holds.) The speed at which both tsunamis travel varies as the square root of the water depth. Therefore, the deep-ocean tsunami travels faster than the local tsunami near shore.

Panel 3—Amplification: Several things happen as the local tsunami travels over the continental slope. Most obvious is that the amplitude increases. In addition, the wavelength decreases. This results in steepening of the leading wave--an important control of wave runup at the coast (next panel). Note that the first part of the wave reaching the local shore is a trough, which will appear as the sea receding far from shore. This is a common natural warning sign for tsunamis. Note also that the deep ocean tsunami has traveled much farther than the local tsunami because of the higher propagation speed. As the deep ocean tsunami approaches a distant shore, amplification and shortening of the wave will occur, just as with the local tsunami shown above.

Panel 4—Runup: Tsunami runup occurs when a peak in the tsunami wave travels from the near-shore region onto shore. Runup is a measurement of the height of the water onshore observed above a reference sea level.Except for the largest tsunamis, such as the 2004 Indian Ocean event, most tsunamis do not result in giant breaking waves (like normal surf waves at the beach that curl over as they approach shore). Rather, they come in much like very strong and fast-moving tides (i.e., strong surges and rapid changes in sea level). Much of the damage inflicted by tsunamis is caused by strong currents and floating debris. The small number of tsunamis that do break often form vertical walls of turbulent water called bores. Tsunamis will often travel much farther inland than normal waves.Do tsunamis stop once on land? No! After runup, part of the tsunami energy is reflected back to the open ocean and scattered by sharp variations in the coastline. In addition, a tsunami can generate a particular type of coastal trapped wave called edge waves that travel back-and forth, parallel to shore. These effects result in many arrivals of the tsunami at a particular point on the coast rather than a single wave as suggested by Panel 3. Because of the complicated behavior of tsunami waves near the coast, the first runup of a tsunami is often not the largest, emphasizing the importance of not returning to a beach many hours after a tsunami first hits.

Tsunami Watch and WarningBecause tsunamis are not easily seen until they are close to shore, researchers and emergency managers rely on monitors that are located throughout the oceans that track slight changes in the height of waves. Whenever there is an earthquake with a magnitude greater than 7.5 in the Pacific Ocean, a Tsunami Watch is automatically declared by the PTWC if it was in a region capable of producing a tsunami.

Once a tsunami watch is issued, PTWC watches tide monitors in the ocean to determine whether or not a tsunami was generated. If a tsunami is generated, a Tsunami Warning is issued and coastal areas are evacuated. In the case of deep ocean tsunamis, the public is normally given time to evacuate, but if it is a locally generated tsunami, a Tsunami Warning is automatically issued and people should immediately evacuate coastal areas.

Tsunamis can wreak havoc on coastal populations and landscapes. The December 26, 2004, tsunami in the Indian Ocean claimed some 150,000 lives and cleared the landscape on millions of acres of oceanfront terrain. Here are some measures you can take to avoid trouble if you're caught in a tsunami.

Safety TipsWhen in coastal areas, stay alert for tsunami warnings.Plan an evacuation route that leads to higher ground.Know the warning signs of a tsunami: rapidly rising or falling coastal waters and rumblings of an offshore earthquake.Never stay near shore to watch a tsunami come in.A tsunami is a series of waves. Do not return to an affected coastal area until authorities say it is safe.

Tsunami Precautions – Safety Tips

Impact of Tsunamis on Human LifeData on the impact of tsunamis from 1900 to mid-2009 was collected via a review of tsunami events from multiple databases and a literature review of publications. Between 1900 and 2009, 94 tsunamis that affected human populations were recorded. There were 255,195 deaths and 48,462 injuries as a result of these tsunamis. Tsunami frequency and deaths were concentrated in the Western Pacific, Southeast Asia, and Americas regions, each of which accounted for almost one third of tsunami events and deaths, but Southeast Asia accounted for 52 percent of the tsunami-affected population from 1900 through 2009 and 95 percent of the tsunami affected population from 1980 through 2009. An estimated 2.5 million people were affected by tsunamis during this time.

World’s Deadliest Tsunamis1) Indian Ocean (Sumatra, Indonesia)Estimated Number of Deaths: 350,000Year: 2004

2) Ancient Greece (Islands of Crete and Santorin)Estimated Number of Deaths: 100,000Year: 1410 B.C.E

3) Portugal, Morocco, Ireland and the United KingdomEstimated Number of Deaths: 100,000Year: 1755

4) Messina, ItalyEstimated Number of Deaths: 100,000Year: 1908

5) South China Sea (Taiwan)Estimated Number of Deaths: 40,000Year: 1782

The Indian Ocean Tsunami Although tsunami's impact is only limited to the coastal areas, it can be enormously destructive. It can It can also affect the entire ocean's basins. In 2004, the Indian Ocean tsunami was marked as the deadliest natural calamities in the history of human. During this disaster, 14 countries having Indian Ocean as their border witnessed more than 2, 30,000 people killed. The first tsunami to struck India was back in December 31, 1881. However, the government of India indicated that around 11,000 people died and more than 5,000 were missing and were assumed dead by the Home Affairs Ministry. An estimation points out that about 380,000 Indians displaced by this tsunami. It is expected that reconstruction of these affected places would cost over 1.2 billion dollars from the World Bank.

Countries effected by the Indian Ocean TsunamiOn December 26, 2004, most of the countries located around the Indian Ocean and Bay of Bengal were struck by tsunami. During this time, the Richter scale measured the earthquake at 8.9 with an epicenter near Sumatra's west coast in Indonesia. The Andaman Island was said to be extensively damaged due to this tsunami. The regions affected the most by tsunami were the Andaman and Nicobar Islands and south-eastern coast.Due to this earthquake resulting tsunami, many countries affected Southeast Asia and area beyond. Countries such as Indonesia, Sri Lanka, India, Thailand, the Maldives, Somalia, Myanmar, Malaysia, Seychelles and many others had to go through the devastating calamities. Several people from countries like Australia and Europe, who had travelled to these tsunami affected areas, lost their lives in this disaster.

Indian Ocean Tsunami in IndiaFactor Andhra Pradesh Kerala Tamil Nadu Pondcherry Total

Population affected 211000 2470000 691000 43000 3415000

Area affected (Ha) 790 Unknown 2487 790 4067

Length of coast affected (Km) 985 250 1000 25 2260

Extent of penetration (Km) 0.5 - 2.0 01/02/12 01/01/05 0.30 - 3.0

Reported height of tsunami (m) 5 03/05/12 07/10/12 10

Villages affected 301 187 362 26 876

Dwelling units 1557 11832 91037 6403 110829

Cattle lost 195 Unknown 5476 3445 9116

Special Thanks to the Sources Used in this Project

-> Google

-> Official Tsunami research paper by Chris Goldfinger (OCU Oceanographer)

-> Mapsofindia.com

-> The Tsunami countdown (book)

-> shree lakshmi library

Special thanks to Dr. Monica Misra, who was a project making inspiration and a true support.

Mansvini misra, X-B