According to the National Oceanic and Atmospheric Administration (NOAA), Tsunamis are giant waves generated by earthquakes or volcanic eruptions under the sea. As tsunami waves plunge into the depths of the ocean, they are not very tall. The forces that the plates produce at their boundaries, where they touch one another, and the flow of the mantle rock beneath the plates are what propel this motion. 

• Waves, however, increase in height as they reach inland depth as the ocean depth decreases.
• In contrast to the distance from the source of the waves, the speed of tsunami waves is determined by ocean depth.
• As they travel through deep water, tsunami waves may travel at the same speed as a jet plane, slowing only as they reach shallow water.
• Tsunamis are generally referred to as tidal waves, but this name is discouraged by oceanographers because tides have little to do with these giant waves.

Causes:

• Earthquake: A tsunami can be generated either by movements along a fault boundary or by movements along a fault line. Tsunamis are not caused by every earthquake. An earthquake needs to meet four conditions before it can generate one, such as:

• Alternatively, the material must slide into the ocean as a result of the earthquake.
• The earthquake must be strong, at least magnitude 6.5 on the Richter Scale.
• The earthquake must rupture the Earth’s surface, and it must occur at a shallow depth – less than 70km below the surface of the Earth.
• A seafloor movement of several meters must result from the earthquake.

• Landslide: Underwater landslides can also initiate tsunamis when the material loosened by the landslide moves violently, pushing the water in front of it. Landslides near the coast can force large amounts of water into the water, disrupting it and causing a tsunami.
• Volcanic eruptions: Volcanic eruptions can be extremely destructive from their immediate source area, though they are relatively infrequent.
• Extra-terrestrial collision: Tsunamis caused by extra-terrestrial collisions (i.e., asteroids, meteors) are an extremely rare occurrence. They have the potential to set a tsunami into action.

On 27th December 2004, tsunami waves struck various countries in the Indian ocean like India, Sri Lanka, Maldives, etc. These Tsunami waves were generated due to an underwater earthquake near Sumatra Island in Indonesia.

Effects:

• Destruction of ports: A tsunami destroys everything on its way, be it residential or commercial areas. Ports are vital for countries’ economic activities and get affected by tsunamis.
• Coastal community: In 2004, thousands of people lost their homes, livelihood, agricultural land, and a lot of people lost their lives etc. Coastal communities are the first ones to bear the brunt of the tsunami.
• Infrastructure: Infrastructures like flyovers, railway lines, bridges, energy facilities like nuclear power plants etc., face a great threat from tsunami waves. Building this infrastructure back takes a lot of time and resources.
• Loss of forest lands: Tsunami waves destroy forests, or small islands get submerged underwater, like what happened in Sri Lanka in 2004 when small islands got submerged. With the submergence of the forest, wild animals also lost their habitat and lost their life.

Under the direction of the Indian National Center for Ocean Information Services (INCOIS), Hyderabad, the Indian Government has established an Early Warning System for the mitigation of such oceanogenic calamities. In accordance with a standard operating procedure, a cutting-edge early warning centre was constructed with the appropriate computational and communication infrastructure to enable the reception of real-time data from sensors, analysis of the data, creation, and transmission of tsunami advisories. During the significant undersea earthquake of 8.4 M that occurred on September 12, 2007, in the Indian Ocean, the effectiveness of this end-to-end system was demonstrated.