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You'd be surprised how much damage four feet of water can do. They're differently-formed waves, after all, so much so that, in the phone books in Auckland, under the disaster preparedness section, they have a section on them. The coolest pieces of advice?
1) Do not go to the beach to watch.
2) If you can see the waves, it is too late to escape.
How's that for finality? I mean, these things can travel across the Pacific in one day.
There's a museum here. Here's some info from there on the forming of them:
How is a tsunami wave different from a normal wave?
The waves you see at the beach are generated by wind blowing over the sea surface. The size of these waves depends on the strength of the wind creating them and the distance over which it blows. Generally the distance between these waves, known as the wavelength, ranges from a couple of feet to perhaps a thousand feet. The speed of these waves as they travel across the ocean ranges from a few miles an hour up to sixty miles an hour in some instances.
Tsunami waves resulting from physical mechanisms ( see above question) behave much differently than wind generated waves. The magnitude of the disturbance causing the tsunami is the primary factor influencing the size and strength of the waves. The height of the wave when it is generated is very small, usually less than a few feet. The distance between successive wave crests or the wavelength however, is much larger than that of a normal wave and may be hundreds of miles apart. Depending on the depth of the water in which the tsunami is traveling, it may attain speeds of up to 500 miles an hour.
How does a tsunami behave as it approaches land?
When the waves of a tsunami approach land, their appearance and behavior become dependent on several local factors. Two of the most important factors are the topography of the seafloor and the actual shape of the shoreline. As a tsunami encounters shallow waters surrounding the shoreline, its height can increase from a meter or less to over 20 meters. Wave heights can also be increased when concentrated on headlands or when traveling into bays having wide entrances that become progressively more narrow. The presence of an offshore coral reef can dissipate the energy of a tsunami, decreasing the impact on the shoreline. Normal wind swell may ride atop of a tsunami wave thereby increasing wave height.
The image most people have of a tsunami is a large, steep wave breaking on the shore. This image is hardly if ever the case. Most tsunamis appear as an advancing tide without having a developed wave face, resulting in rapid flooding of low-lying coastal areas. Sometimes, a bore can form during which an abrupt front of whitewater will rapidly advance inland much similar to the tidal bore formed at the mouth of large rivers.
Another rare event that may result from a tsunami is a standing wave or seiche. A seiche occurs in bodies of water that are partially or completely enclosed, such as Hilo Bay, creating a standing wave that continually sloshes back and forth. The appearance of a seiche would be very similar to what happens when you place a glass of water on the table; the water rocks back and forth before settling. When a seiche is generated by a tsunami, subsequent tsunami waves may arrive in unison with a seiche resulting in an increase in the drawdown in sea level and a dramatic increase in wave height. Seiche waves may continue several days after a tsunami.
This earthquake could've been a lot worse, I suspect - isn't it just derailment, an industrial fire and about 300 people injured so far? Given the preparedness of the place, and the remote location of the epicentre, I'm not surprised it's had so little effect so far. |
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