What is Tsunami?

Tsunami disaster

What is Tsunami?

Tsunami is a Japanese word with the English translation, "harbor wave." The phenomenon we call tsunami is a series of large waves of extremely long wavelength and period usually generated by a violent, impulsive undersea disturbance or activity near the coast or in the ocean. When a sudden displacement of a large volume of water occurs, or if the sea floor is suddenly raised or dropped by an earthquake, big tsunami waves can be formed by forces of gravity. Earthquakes, landslides, volcanic eruptions, explosions, and even the impact of cosmic bodies, such as meteorites, can generate tsunamis. Tsunamis can savagely attack coastlines, causing devastating property damage and loss of life.

How do earthquakes generate tsunamis?

Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Tectonic earthquakes are a particular kind of earthquakes that are associated with the earth's crustal deformation; when these earthquakes occur beneath the sea, the water above the deformed area is displaced from its equilibrium position. Waves are formed as the displaced water mass, which acts under the influence of gravity, attempts to regain its equilibrium. When large areas of the sea floor elevate or subside, a tsunami can be created.

What happens when a tsunami encounters land?

Just like other water waves, tsunamis begin to lose energy as they rush onshore - part of the wave energy is reflected offshore, while the shoreward-propagating wave energy is dissipated through bottom friction and turbulence. Despite these losses, tsunamis still reach the coast with tremendous amounts of energy. Tsunamis have great erosional potential, stripping beaches of sand that may have taken years to accumulate and undermining trees and other coastal vegetation. Capable of inundating, or flooding, hundreds of meters inland past the typical high-water level, the fast-moving water associated with the inundating tsunami can crush homes and other coastal structures. Tsunamis may reach a maximum vertical height onshore above sea level, often called a run up height, of 10, 20, and even 30 meters.

Speed of tsunami

Tsunami wave can travel at the speed of a commercial jet plane, over 800 km/h. They can move from one side of the Pacific Ocean in less than a day. The waves can be extremely dangerous and damaging when they reach the shore.

What should you do?

1. If you are at home and hear there is a tsunami warning, you should make sure your entire family is aware of the tsunami. Your family should evacuate your house if you live in a tsunami evacuation zone.

2. If you are at the beach or near the ocean and you feel the earth shake, move immediately to higher ground. Do not wait for a tsunami warning to be announced.

3. If you are on a ship or boat, do not return to port if you are at sea and a tsunami warning has been issued for your area. Tsunami can cause rapid changes in water level and unpredictable dangerous current in harbours and ports.

The phenomenon we call "tsunami" (soo-NAH-mee) is a series of traveling ocean waves of extremely long length generated by disturbances associated primarily with earthquakes occurring below or near the ocean floor. Underwater volcanic eruptions and landslides can also generate tsunamis. In the deep ocean, their length from wave crest to wave crest may be a hundred miles or more but with a wave height of only a few feet or less. They cannot be felt aboard ships nor can they be seen from the air in the open ocean. In deep water, the waves may reach speeds exceeding 500 miles per hour.

Tsunamis are a threat to life and property to anyone living near the ocean. For example, in 1992 and 1993 over 2,000 people were killed by tsunamis occurring in Nicaragua, Indonesia and Japan. Property damage was nearly one billion dollars. The 1960 Chile Earthquake generated a Pacific-wide tsunami that caused widespread death and destruction in Chile, Hawaii, Japan and other areas in the Pacific. Large tsunamis have been known to rise over 100 feet, while tsunamis 10 to 20 feet high can be very destructive and cause many deaths and injuries.

The Tsunami Warning System (TWS) in the Pacific, comprised of 26 participating international Member States, monitors seismological and tidal stations throughout the Pacific Basin. The System evaluates potentially tsunamigenic earthquakes and disseminates tsunami warning information. The Pacific Tsunami Warning Center (PTWC) is the operational center of the Pacific TWS. Located in Honolulu, Hawaii, PTWC provides tsunami warning information to national authorities in the Pacific Basin.

How do tsunami differ from other water waves?
Tsunamis are unlike the wind-generated waves on local lakes or coastal beaches, in that they are characterized as shallow-water waves, with long periods and wavelengths. The wind-generated swell like the one at a California beach spawned by a storm out in the pacific and rhythmically rolling in, one wave after another might have a period of about 10 seconds and a wavelength of 150 m. A tsunami, on the other hand, can have a wavelength in excess of 100 km and period on the order of one hour. As a result of their long wave lengths tsunami behave as shallow-water waves. A wave becomes a shallow water wave when the ratio between the water depth and its wave length gets very small. Shallow-water waves move at a speed that is equal to the square root of the product of the acceleration of gravity (9.8 m/s/s) and the water depth. This means, in the Pacific Ocean, where the typical water depth is about 4000m, a tsunami travels at about 200m/s, or over 700 700km/hr. Because the rate at which a wave losses its energy is inversely related to its wavelength, tsunami not only propagate at high speeds, they can also travel great, transoceanic distances with limited energy losses. The wave crests bend as the tsunami travels—is called refraction. Wave refraction is caused by segments of the wave moving at different speeds as the water depth along the crest varies.

How does earthquake generate tsunami?
Tsunami can be generated when the see floor abruptly deforms and vertically displaces the overlying water. Tectonic earthquakes are a particular kind of earthquake that are associated with the earth’s crustal deformation, when these earthquakes occur beneath the see, the water above the deformed area is displayed from its equilibrium position. Waves are formed as the displaced water mass, which acts under the influence of gravity, attempts to regain its equilibrium.


Tsunami safety Rules:
An earthquake in an area is a natural tsunami warning. Do not stay in low-lying coastal areas after a strong earthquake has been felt.

A tsunami is not a single wave, but a series of waves. Stay out of danger areas until competent authority issues an “all-clear”.

All tsunamis like hurricanes are potentially dangerous; even though they may not damage every coastline they strike.

Never go down to the shore to watch for a tsunami. When see the wave you are too close to escape it. Never try to surf a tsunami; tsunamis do not curl or break like surfing waves.

Sooner or later, tsunamis visit every coastline in the Pacific. Warnings apply to you if you live in any Pacific coastal area.

Tsunami warning Organization

ITIC:
The International Tsunami Information Center (ITIC) was established in Honolulu, in November 1965, by the Intergovernmental Oceanographic Commission (IOC) of the United Nations Educational, Scientific and Cultural Organization (UNESCO).
In 1968, IOC formed an International Coordination Group for the Tsunami Warning System in the Pacific (ICG/ITSU).

The present Member States are:
Australia, Canada, Chile, China, Colombia, Cook Islands, Costa Rica, Democratic People’s Republic of Korea, Ecuador, El Salvador, Fiji, France, Guatemala, Indonesia, Japan, Mexico, New Zealand, Nicaragua, Peru, Republic of the Philippines, Republic of Korea, Russian Federation, Samoa, Singapore, Thailand, and the United States of America.

The International Tsunami Warning System in the Pacific is one of the most successful international scientific programs with the direct humanitarian aim of mitigating the effects of tsunami by saving lives and property.

Damages: Loss or harm caused by a destructive tsunami. More specifically, the damage caused directly by tsunamis can be summarized into the following: 1) deaths and injuries; 2) houses destroyed, partly destroyed, inundated, flooded, or burned; 3) other property damage and loss; 4) boats washed away, damaged or destroyed; 5) lumber washed away.