Tsunami is a Japanese word meaning ‘harbour wave’. A tsunami is a long, high sea wave, produced by a disturbance, such as a volcanic eruption, submarine earthquake or coastal landslide.
In other words, a tsunami is a series of ocean waves that sends surges of water, sometimes reaching heights of over 100 feet (30.5 meters), onto land. These walls of water can cause widespread destruction when they crash ashore.
Local Tsunami: A local tsunami is a tsunami that causes damage in relatively close proximity to the tsunami-causing event. Specifically, the underwater event (usually an earthquake) that produces a local tsunami happens within 100 km, which is a little over 60 miles, of the land damage that results.
Regional Tsunami: A regional tsunami is one that causes damage from 100 km to 1,000 km from the underwater event that causes the tsunami. Regional tsunamis provide slightly more warning time than local tsunamis, making landfall between one and three hours of the event that causes them.
Distant Tsunami: A distant tsunami, also called a tele-tsunami or ocean-wide tsunami. It originates with an exceptionally powerful and destructive event more than 1,000 km away from landfall. Though a distant tsunami may first appear like a local tsunami, it travels across wide swathes of ocean basin. There is more time to evacuate and escape a distant tsunami, but it also covers a larger mass of land and tends to cause extensive and widespread destruction.
Signs of an approaching tsunami:
- An earthquake may be felt.
- Large quantities of gas may bubble to the water surface and make the sea look as if it is boiling.
- The water in the waves may be unusually hot.
- The water may smell of rotten eggs (Hydrogen Sulphide) or of petrol or oil.
- The water may sting the skin.
- The sea may recede to a considerable distance.
- A flash of red light might be seen near the horizon.
- As the wave approaches the top of the wave may glow red.
- Tsunamis may also be caused by underwater landslides or volcanic eruptions. They may even be launched, as they frequently were in Earth’s ancient past, by the impact of a large meteorite plunging into an ocean.
- Tsunami can be generated when the sea floor abruptly deforms and vertically displaces the overlying water.
- A tsunami can be generated when thrust faults associated with convergent or destructive plate boundaries move abruptly, resulting in water displacement, owing to the vertical component of movement involved.
- Movement on normal (extensional) faults can also cause displacement of the seabed, but only the largest of such events (typically related to flexure in the outer trench swell) cause enough displacement to give rise to a significant tsunami, such as the 1977 Sumba and 1933 Sanriku events.
- In the 1950s, it was discovered that larger tsunamis than had previously been believed possible could be caused by giant submarine landslides. These rapidly displace large water volumes, as energy transfers to the water at a rate faster than the water can absorb. Their existence was confirmed in 1958, when a giant landslide in Lituya Bay, Alaska, caused the highest wave ever recorded, which had a height of 524 metres.
- There has been considerable speculation on the possibility of using nuclear weapons to cause tsunamis near an enemy coastline.
- Damage and Destruction: Destruction is caused by two mechanisms: the smashing force of a wall of water traveling at high speed, and the destructive power of a large volume of water draining off the land and carrying all with it, even if the wave did not look large. Objects and buildings are destroyed by the sheer weight of the water, often reduced to skeletal foundations and exposed bedrock.
- Death: There is very little warning before Tsunamis hit. This means that people living in towns and villages on the coast do not have time to escape. Hundreds and thousands of people are killed by Tsunamis.
- The tsunami that struck South Asia and East African on Decmber 24 2004 killed a staggering 31,187 people in Sri Lanka. There were 4,280 missing people and a further 23,189 were injured.
- Serious Environmental Changes: After a tsunami strikes, landscapes that previously constituted picturesque beaches or seaside towns become a wasteland. In addition to the destruction of human construction, tsunamis destroy vegetation such as trees, resulting in landslides and coastlines that slip into the sea as deep root systems that previously held land in place get ripped out.
- Psychological effects: These people were suffering from grief and depression as their homes, businesses and loved ones were taken from them. A study by the World Health Organisation on survivors of the tsunami in Sri Lanka on December 24, 2004 found that three to four weeks after the tsunami between 14 and 39 per cent of the children had post-traumatic stress disorder (PTSD).
- Disease and Contamination: After a tsunami, contaminated water and food supplies pose a risk to people's health. Flood waters can carry many sources of contamination such as dirt or oil. In addition, infectious diseases increase after a tsunami. Malaria and cholera may become more common.
- Site Buildings or infrastructure away from hazard area or locate on a high point.
- Saving lives is to develop proper warning systems and research ways of predicting tsunamis before they happen. This would not save buildings but it could definitely save people’s lives, as they would have time to evacuate the area. Places of safety would have to be set up though, or the result would be a huge refugee crisis, and people would end up starving instead of drowning.
- Infrastructure is also required to slow water down. Berms, ditches and slopes can all help to slow down the water, as can plant trees.
- Know the warning signs of a tsunami: rapidly rising or falling coastal waters and rumblings of an offshore earthquake.
- Water can be steered to strategically place angled walls, ditches and paved roads. Theoretically, porous dikes can reduce the impact of violent waves.
- Plan an evacuation route that leads to higher ground.