Tsunamis

Com essa tragédia toda acontecendo no Japão, eis o personagem principal aparece de novo: o terrível TSUNAMI.

Mas você sabe como ele se forma? Por que ele é tão devastador?

Saiba mais sobre esse que é sem dúvida um dos fenômenos naturais mais aterrorizantes. Leia o texto abaixo e preencha as lacunas com uma variação da palavra entre parênteses.

Tsunami

A tsunami (plural: tsunamis or tsunami; from Japanese: 津波, lit. “harbor wave”; English pronunciation: /tsuːˈnɑːmiː/, tsoo-NAH-mee or /suːˈnɑːmiː/, soo-NAH-mee), also called a tsunami wave train, or less frequently a tidal wave, is a series of water waves caused by the __________(PLACE) of a large volume of a body of water, usually an ocean, though it can occur in large lakes. Tsunamis are a frequent __________(OCCUR) in Japan; approximately 195 events have been recorded. Owing to the immense volumes of water and the high energy involved, tsunamis can devastate __________(COAST) regions.

Earthquakes, volcanic eruptions and other underwater explosions (including detonations of underwater nuclear devices), landslides and other mass movements, meteorite ocean impacts or similar impact events, and other disturbances above or below water all have the potential to generate a tsunami.

The Greek__________(HISTORY)Thucydides was the first to relate tsunami to submarine earthquakes,^[5][6] but the understanding of a tsunami’s nature remained slim until the 20th century and is the subject of ongoing research. Many early geological, geographical, and __________(OCEAN) texts refer to tsunamis as “seismic sea waves.”

Some meteorological conditions, such as deep depressions that cause tropical cyclones, can generate a storm surge, called a meteotsunami, which can raise tides several metres above normal levels. The displacement comes from low atmospheric __________(PRESS) within the centre of the depression. As these storm surges reach shore, they may resemble (though are not) tsunamis, inundating vast areas of land.

Characteristics

When the wave enters shallow water, it slows down and its amplitude (height) increases.

The wave further slows and amplifies as it hits land. Only the largest waves crest.

Tsunamis cause damage by two mechanisms: the smashing force of a wall of water travelling at high speed, and the __________(DESTROY) power of a large volume of water draining off the land and carrying all with it, even if the wave did not look large.

While everyday wind waves have a wavelength (from crest to crest) of about 100 metres (330 ft) and a height of roughly 2 metres (6.6 ft), a tsunami in the deep ocean has a wavelength of about 200 kilometres (120 mi). Such a wave travels at well over 800 kilometres per hour (500 mph), but owing to the enormous wavelength the wave oscillation at any given point takes 20 or 30 minutes to complete a cycle and has an amplitude of only about 1 metre (3.3 ft).^[20] This makes tsunamis difficult to detect over deep water. Ships rarely notice their __________(PASS).

As the tsunami approaches the coast and the waters become shallow, wave shoaling compresses the wave and its velocity slows below 80 kilometres per hour (50 mph). Its wavelength diminishes to less than 20 kilometres (12 mi) and its __________(AMPLE) grows enormously. Since the wave still has the same very long period, the tsunami may take minutes to reach full height. Except for the very largest tsunamis, the __________(APPROACH) wave does not break, but rather appears like a fast-moving tidal bore. Open bays and coastlines adjacent to very deep water may shape the tsunami further into a step-like wave with a steep-breaking front.

When the tsunami’s wave peak reaches the shore, the resulting temporary rise in sea level is termed run up. Run up is measured in metres above a __________(REFER) sea level. A large tsunami may feature multiple waves arriving over a period of hours, with __________(SIGN) time between the wave crests. The first wave to reach the shore may not have the highest run up.^[22]

About 80% of tsunamis occur in the Pacific Ocean, but they are possible wherever there are large bodies of water, including lakes. They are caused by earthquakes, landslides, volcanic explosions, and bolides.

Drawback

Wave animation showing the initial “drawback” of surface water

If the first part of a tsunami to reach land is a trough—called a drawback—rather than a wave crest, the water along the shoreline recedes __________(DRAMA), exposing normally submerged areas.

A drawback occurs because the water propagates outwards with the trough of the wave at its front. Drawback begins before the wave arrives at an interval equal to half of the wave’s period. Drawback can exceed hundreds of metres, and people unaware of the danger sometimes remain near the shore to satisfy their curiosity or to collect fish from the exposed seabed.

 

Incrível, não é mesmo? Não deixe de assistir ao vídeo abaixo porque é de cair o queixo.

Ah, e para conferir as respostas do exercício acima, é só clicar aqui.