Tsunami is one of the most powerful and most devastating forces in nature. Tsunami has been known to human population settled around coastal areas for thousands and thousands of years, but the first written testimonies date from few hundred years BCE. Although Tsunami has different names in different parts of the world, the word Tsunami comes from Japanese language, and is widely accepted as the name for this natural phenomenon through the world.
The devastating force of tsunami became widely known after 2004 Indian Ocean tsunami, when over 230,000 people were killed in 14 countries. There are a few reasons why tsunamis are so destructive; first of all, tsunami is mostly generated by earthquakes, volcanic eruptions, and landslides at the bottom of the oceans, and therefore, it is very often unnoticed because the huge volume of water is displaced, many hundred meters or even kilometers under the surface. As a consequence, a wave is formed with a very long wavelength (sometimes hundreds of kilometers long) and a very small wave height, and that is why it often travels hundreds of kilometers virtually unnoticed as it forms a very small wave on the surface, most of the time about only 30 centimeters. That is why the ships and boats sailing of shore cannot recognize such a wave as a sign of tsunami and it often happened that fisherman came ashore only to find out that their villages literally do not exist anymore, while they haven’t noticed anything conspicuous during their time at the sea. However, tsunami wave dramatically grows in height as it reaches shallower water. Although the wave sometimes travels at 800 kilometers per hour or even more, it abruptly slows down when it reaches shallow waters decreasing its speed below 80 kilometers per hour. The clash with coast also diminishes tsunami’s wavelength to less than 20 kilometers, but its wave height takes over the overall power of the tsunami wave as it increases up to 14-30 meters high or more. The highest recorded wave was 524 meters; it was caused by a giant land slide in Alaska in 1958. Another reason why tsunamis are so devastating is that they can travel huge distances and reach many shores and countries, as it happened in 2004 Indian Ocean tsunami, or when an earthquake occurred in Alaska in 1946 and 14 meters tsunami caused by it reached Hawaii. Such tsunamis caused by so cold mega thrust earthquakes are known as telletsunamis because they can travel across the entire oceans. The third reason why tsunamis are so destructive is that not only that the huge wall of water smashes the shore with unimaginable force, but it also drains of the land almost immediately carrying with it an enormous amount of debris consisting of trees, cars, and entire houses, producing a deadly smashing force which sweeps everything in its path. Unfortunately, most people are killed and drowned by the debris of the draining wave.
Although most tsunamis are caused by earthquakes, landslides, and volcanic eruptions, they are sometimes triggered by glacier calving and sometimes even by meteorites and nuclear tests. Most tsunamis, almost 80% occur in the Pacific Ocean; other 20% occur mostly in Indian Ocean, but they sometimes happen in the Atlantic Ocean, in the seas, and even in the big lakes. Although people were trying for centuries to predict tsunamis, and although the 2004 Indian Ocean tsunami raised the necessity to predict such a brutal force, it is not always possible to predict tsunamis, even when the location of an earthquake is detected. Fortunately, there are some, although short notice, signs which announce tsunami and the most obvious one is a drawback which is a very unusual phenomenon consisting of coastal waters drawing back to the ocean, reseeding dramatically and exposing hundreds of meters of shore line which is normally submerged in water. Drawbacks are even accompanied by an eerie sucking sound as the ocean literally sucks the huge amount of coastal water. Sometimes, people, especially tourists, got killed because they are driven by curiosity to explore the exposed shores. Little do they know that tsunami proceeds almost immediately after the drawback. After the 2004 Indian Ocean tsunami, seismologists, oceanographers and geologists started to conceive a more efficient warning and predicting system hoping it will provide that in future there will be no more massive causalities. The system provides warnings immediately after the earthquake, which should give enough time for the coastal guards to warn the inhabitants to promptly leave the shore line area, saving their lives. Such warning systems are mainly based on the bottom pressure sensors attached to buoys which constantly monitor the pressure over the overlying water column. It is interesting to notice that some animals apparently have the ability to immediately predict earthquakes and tsunamis, especially elephants who normally communicate trough low wave or infrasound, so it is quite possible that they can detect the deep underwater rumbling sound which human ear cannot reach. Even though such animal ability cannot be used as a warning system there are many reports in the 2004 Indian Ocean earthquake that some animals escaped to the higher ground minutes before the tsunami.
Hopefully, in the future, technology will provide an efficient warning system which will enable people from coastal area to evacuate in advance and save their lives.
