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Anna Posyniak‑Dutka Tsunami

1. The Name

Nowadays we know quite a lot about the mechanisms behind the formation of tsunami wavestsunami waves [tsunami wave]tsunami waves, but the name of the phenomenon was coinedcoined [coin]coined at the time when people had no means to track down the origin of natural events. However, it’s only fair to say that the name tsunami, which means harbour wave, hasn’t lost its adequacy. We know now that tsunami waves are barely noticeablebarely noticeablebarely noticeable on the high seashigh seashigh seas, while their staggering potencystaggering potencystaggering potency can cause catastrophic damage on the coast.

2. Mechanism of Creation

Tsunami waves are caused by a number of natural phenomena. Among them there are earthquakes on the ocean’s floorearthquakes on the ocean’s floor [earthquake on the ocean’s floor]earthquakes on the ocean’s floor, eruptions of underwater volcanoeseruptions of underwater volcanoes [eruption of an underwater volcano]eruptions of underwater volcanoes, submarine landslidessubmarine landslides [submarine landslide]submarine landslides, and meteorite hitsmeteorite hits [meteorite hit]meteorite hits. It’s worth mentioning that tsunamis can also be triggeredtriggered [trigger]triggered by human activity. Nuclear testing programmesnuclear testing programmes [nuclear testing programme]Nuclear testing programmes, during which underwater explosions were carried out, caused tsunamis at Bikini Atoll in 1946 and at Mururoa Atoll in 1970. What do these natural phenomena and nuclear blastsnuclear blasts [nuclear blast]nuclear blasts have in common to create giant destructive waves? The answer is quite simple: it’s a generated impulse. All of these events release huge amounts of energyrelease huge amounts of energy [release huge amount of energy]release huge amounts of energy which displaces enormous masses of waterdisplaces enormous masses of water [displace enormous mass of water]displaces enormous masses of water. The energy pushes water up to the surface and further above the ocean level where gravity pulls it down again. That breaks the mass of water into waves and the tsunami comes into existencecomes into existence [come into existence]comes into existence.

3. Characteristics

Tsunamis are most common in the basin of the Pacific Ocean.    In the open ocean, tsunami waves are not only hard to spot but also rather harmlessharmlessharmless. Nevertheless, they still have huge proportions and can travel at incredible speeds. They can reach above 500 mph, which is almost 900 kmh. The waves can be hundreds of kilometres long, but their height at this point is hardly ever bigger than a couple of dozen centimetres. When the waves approach the land, frictionfrictionfriction with the rising sea bottom makes them slow down. That in turn increases the waves’ amplitudeswaves’ amplitudes [wave’s amplitude]waves’ amplitudes. The waves that hit the land can be as high as a couple of dozen metres. The highest tsunami wave ever recorded was 524 metres high and occured in the Lituya Bay in Alaska in 1958.

4. The Impact

Sometimes before the main wave hits the land, the water will withdrawwithdrawwithdraw farther than normal. It’s definitely a sign that should warn people in close proximityin close proximityin close proximity to the coast. It might be just enough time to escape to a higher land. Depending on the potencypotencypotency of the wave and the terrain it enters, a tsunami can flood an area many miles inside the land. It will drown people and animals, level houseslevel houses [level a house]level houses, uproot treesuproot trees [uproot a tree]uproot trees, and damage everything else on its way. What’s more, the water will retreatretreatretreat, carrying with it all newly created debrisdebrisdebris and causing further damage.

5. Prevention and Protection

Countries frequently affected by tsunamis make efforts to monitor and detect any events that can potentially lead to the formation of tsunami waves. They issue alertsissue alerts [issue an alert]issue alerts and evacuate people who are most likely to be in danger of losing their lives. Some countries, such as Japan, construct special seawallsseawalls [seawall]seawalls and flood gatesflood gates [flood gate]flood gates which are expected to lessen the impact oflessen the impact oflessen the impact of an approaching wave before it reaches the coast. Another solution is channels, the purpose of which is to divert incoming and outflowing water surgedivert incoming and outflowing water surgedivert incoming and outflowing water surge saving the infrastructure from being inundatedinundated [inundate]inundated. Unfortunately, as the incident from 2011 shows, it’s not always effective.

1 Źródło: Anna Posyniak‑Dutka, licencja: CC BY-SA 3.0.