Introduction
The term Tsunami has been derived from a Japanese term Tsu meaning ‘harbor’ and nami meaning ‘waves’. Tsunamis are popularly called tidal waves but they actually have nothing to do with the tides
These waves which often affect distant shores, originate by rapid displacement of water from the lake or the sea either by seismic activity, landslides, volcanic eruptions or large meteoroid impacts.
What ever the cause may be sea water is displaced with a violent motion and swells up, ultimately surging over land with great destructive power. The effects of a tsunami can be unnoticeable or even destructive.
A tsunami is a series of ocean waves with very long wavelengths (typically hundreds of kilometers) caused by large-scale disturbances of the ocean, such as: earthquakes, volcanic eruptions, and underwater landslides. Tsunamis can travel across the ocean at high speeds and grow in height as they approach the shore, causing widespread damage and flooding when they reach land. They can affect coastlines thousands of kilometers away from the source of the disturbance and can cause significant loss of life and property damage. It’s important for coastal communities to have evacuation plans and to be prepared for the possibility of a tsunami.
Tsunamis are large, powerful waves that are caused by earthquakes, volcanic eruptions, landslides, or other disturbances in the ocean. They can travel hundreds of miles per hour and cause devastating destruction when they reach land. Tsunamis can be very destructive, flooding coastal areas
What is a Tsunami?
The series of extremely long waves, Tsunami are very long wavelengths of water caused by a large and sudden displacement of the ocean due to earthquakes, volcanic eruptions etc.
These are also called seismic sea waves and are one of the most powerful and destructive natural forces.
When they reach the coast, they can cause dangerous coastal flooding and powerful currents that can last for several hours or days.
Most tsunamis are caused by large earthquakes. Though, not all earthquakes cause tsunamis.
Tsunami are waves caused by sudden movement of the ocean surface due to earthquakes, landslides on the sea floor, land slumping into the ocean, large volcanic eruptions or meteorite impact in the ocean.
https://appliedsciences.nasa.gov
Types of Tsunami
- Tidal Wave Tsunami
2. Seismic Tsunami
3. Volcanic Tsunami
4. Meteorological Tsunami
5. Landslide Tsunami
Tidal Wave Tsunami
A tidal wave tsunami is a type of tsunami caused by the gravitational pull of the moon and sun on the Earth’s oceans, leading to the rise and fall of sea levels. This results in the formation of large ocean waves, which can travel long distances and cause widespread damage when they reach the shore. Tidal wave tsunamis are not related to tsunamis caused by earthquakes, volcanic eruptions, or other geological events.
Seismic Tsunami
Seismic tsunamis are caused by underwater earthquakes, which can displace large volumes of water and generate ocean waves. They can be extremely destructive, with waves reaching heights of several meters and traveling long distances across the ocean. Seismic tsunamis are the most common type of tsunamis and are responsible for the majority of the damage and casualties caused by tsunamis.
Volcanic Tsunami
Volcanic tsunamis occur when a volcanic eruption under the ocean displaces a large volume of water, generating a tsunami. They can also be generated by underwater volcanic landslides. Volcanic tsunamis are less common than seismic tsunamis, but can still be extremely destructive and pose a threat to coastal communities.
Meteorological Tsunami
Meteorological tsunamis are generated by meteorological events such as strong storms (tropical cyclones, extratropical cyclones) and wind waves. They typically occur in shallow coastal waters and can cause significant coastal flooding and erosion. Meteorological tsunamis are not as destructive as seismic and volcanic tsunamis but can still pose a threat to coastal communities, especially in low-lying areas.
Meteorological tsunamis, also known as meteorological storm surges, are tsunamis generated by extreme weather events such as hurricanes and typhoons. They are caused by the strong winds and low pressure associated with these storms, which can raise the sea level and displace water, leading to a tsunami. Meteorological tsunamis are less common than seismic and volcanic tsunamis, but can still cause significant damage to coastal communities.
Landslide Tsunami
Landslide tsunamis are generated by the rapid movement of large masses of rock, soil, and debris into the ocean. This movement can displace a large volume of water, generating a tsunami. Landslide tsunamis can be caused by a variety of factors, including earthquakes, volcanic eruptions, and coastal erosion. They are less common than other types of tsunamis, but can still be extremely destructive, especially in areas with steep coastal slopes and loose soils.
Causes of Tsunami
A Tsunami can be generated only through the vertical movement of the seafloor. Most Tsunamis are generated by earthquakes. Volcanic eruption, underwater explosion, landslides and meteorite impacts are some other causes of Tsunami.
https://en.wikipedia.org/wiki/Tsunamis_in_lakes
Earthquake
Tsunami is generated by the earthquake because of the disturbance of the seafloor and is formed generally with vertical displacement. Most Tsunami is generated by earthquakes that occur along the subduction boundaries of plates along the ocean trenches. The size of the Tsunami is related to the size of the earthquake.
Underwater explosion
A Nuclear Testing by the US generated Tsunami in 1940 and 1950s in Marshall island.
Volcanic eruption
Volcanoes that occur along the Coastal waters can cause several effects that can cause a tsunami.
Landslides
Earthquake and volcanic eruptions generally generate landslides, these landslides when moving into the Oceans, bays and lakes can generate Tsunami. The tsunami is a landslide either occurring under water or originating above the sea and then plunging into the water. The largest tsunami ever produced by a landslide was in Lituya
Meteorite Impacts
Though no historic example as such of meteorite impact has caused Tsunami, the apparent impact of a meteorite about 5 million years ago produced Tsunami leaving deposits along the Gulf Coast of Mexico and the United States
General Characteristics
Tsunami differs from ordinary ocean waves, which are produced by wind blowing over water. The tsunamis travel much faster than ordinary waves. Compared to normal wave speed of 100 kilometers per hour, tsunami in the deep water of the ocean may travel the speed of a jet airplane – 800 kilometers per hour! And yet, in spite of their speed, tsunami increases the water height only 30-45cm and often passes unnoticed by ships at sea.
Contrary to the popular belief, the tsunami is not a single giant wave. It is possible for a tsunami to consist of ten or more waves which is then termed as ‘tsunami wave train’. The waves follow each other 5 to 90 minutes apart. Tsunami normally causes flooding as a huge wall of water enters the main land.
Predictability
There are two distinct types of tsunami warning:
a) International tsunami warning systems and
b) Regional warning systems.
Tsunamis have occurred in all the oceans and in the Mediterranean Sea, but the great majority of them have occurred in the Pacific Ocean. Since scientists cannot exactly predict earthquakes, they also cannot exactly predict when a tsunami will be generated.
International Tsunami Warning Systems
International Tsunami Warning Systems shortly after the Hilo Tsunami (1946), the Pacific Tsunami Warning System (PTWS) was developed with its operational center at the Pacific Tsunami Warning Center (PTWC) near Honolulu, Hawaii. The PTWC is able to alert countries several hours before the tsunami strikes. The warning includes predicted arrival time at selected coastal communities where the tsunami could travel in few hours. A tsunami watch is issued with subsequent arrival time to other geographic areas.
Regional warning systems
Regional Warning Systems usually use seismic data about nearby earthquakes to determine if there is a possible local threat of a tsunami. Such systems are capable enough to provide warnings to the general public in less than 15 minutes.
In India, the Survey of India maintains a tide gauge network along the coast of India. The gauges are located in major ports as shown in the figure The day-to-day maintenance of the gauge is carried with the assistance from authorities of the ports.
Apart from the tide gauge, tsunami can be detected with the help of radars. The 2004 Indian Ocean tsunami, recorded data from four radars and recorded the height of tsunami waves two hours after the earthquake.
It should be noted that the satellites observations of the Indian Ocean tsunami would not have been of any use in delivering warnings, as the data took five hours to process and it was pure chance that the satellites were overhead at that time. However, in future it is possible that the space-based observation might play a direct role in tsunami warning.
Typical Adverse Effects
Local tsunami events or those less than 30 minutes from the source cause the majority of damage. The force of the water can raze everything in its path. It is normally the flooding affect of the tsunami that causes major destruction to the human settlements, roads and infrastructure thereby
disrupting the normal functioning of the society. Withdrawal of the tsunami causes major damage.
As the waves withdraw towards the ocean they sweep out the foundations of the buildings, the beaches get destroyed and the houses carried out to sea.
Damage to ports and airports may prevent importation of needed food and medical supplies. Apart from the physical damage, there is a huge impact on the public health system. Deaths mainly occur because of drowning as water inundates homes. Many people get washed away or crushed by the giant waves and some are crushed by the debris, causes.
There are very few evidences which show that tsunami flooding has caused large scale health problem.
Availability of drinking water has always been a major problem in areas affected by a disaster. Sewage pipes may be damaged causing major sewage disposal problems. Open wells and other ground water may be contaminated by salt water and debris and sewage. Flooding in the locality may lead to crop loss, loss of livelihood like boats and nets, environmental degradation etc.
History of Tsunami’s in India
1881 Andaman and Nicobar Islands Tsunami: A tsunami that struck the Andaman and Nicobar Islands, caused by an earthquake in the Bay of Bengal. Killing more than 2,000 people.
1946 Tsunami in Andaman and Nicobar Islands: A tsunami generated by a powerful earthquake in the Andaman Sea, causing widespread damage to the Andaman and Nicobar Islands.
1991 Maldives Tsunami: A tsunami that hit the Maldives and the coast of India, resulting from an underwater earthquake in the Indian Ocean.
2004 Indian Ocean Tsunami: One of the deadliest tsunamis in history, caused by a massive underwater earthquake off the coast of Sumatra. It affected the entire Indian Ocean region, including India’s east coast.
These tsunamis have caused significant loss of life and property, and have prompted the Indian government to implement measures to mitigate the impact of future tsunamis.
Even though India has not faced frequent Tsunamis but there is a need to identify the areas that are generally affected by Tsunamis. The whole of the Indian coastal belt is prone to Tsunami. Table shows incidents of tsunamis that have affected our country.
their effectiveness has been questioned, as tsunamis are often higher than the barriers. For instance, the tsunami which hit the island of Hokkaido on July 12, 1993 created waves as much as 30m (100 ft) tall – as high as a 10-story building. The port town of Aonae on Hokkaido was completely surrounded by a tsunami wall, but the waves washed right over the wall and destroyed all the wood
Possible Risk Reduction Measures
While it is of course not possible to prevent a tsunami, in certain tsunami prone countries some measures have been taken to reduce the damage caused on shore.
Japan has implemented an extensive programme of building tsunami walls of up to 4.5m (13.5 ft) high in front of populated coastal areas. Other localities have built flood gates and channels to redirect the water from incoming tsunamis.
However, framed structures in the area. The wall may have succeeded in slowing down and moderating the height of the tsunami but it did not prevent major destruction and loss of life.
Some other systematic measures to protect coastlines against tsunamis include:
Site Planning and Land Management- Within the broader framework of a comprehensive plan, site planning determines the location, configuration, and density of development on particular sites and is, therefore, an important tool in reducing tsunami risk.
The designation and zoning of tsunami hazard areas for such open-space uses as agriculture, parks and recreation, or natural hazard areas is recommended as the first land use planning strategy. This strategy is designed to keep development at a minimum in hazard areas.
In areas where it is not feasible to restrict land to open-space uses, other land use planning measures can be used. These include strategically controlling the type of development and uses allowed in hazard areas, and avoiding high-value and high- occupancy uses to the greatest degree possible.
While the Mercalli scale describes the intensity of an earthquake based on its observed effects, the Richter scale describes the earthquake’s magnitude by measuring the seismic waves that cause the earthquake. The two scales have different applications and measurement techniques. The Mercalli scale is linear and the Richter scale is logarithmic. i.e. a magnitude 5 earthquake is ten times as intense as a magnitude 4 earthquake.