From Ocean Teacher Library
Strengthening Tsunami Warning and Emergency ResponseContents |
Tsunami derives from the Japanese term meaning wave (“nami”) in a harbor
(“tsu”). It refers to a series of traveling waves of extremely long length and
period, usually generated by disturbances associated with earthquakes occurring
below or near the ocean floor (also called seismic sea wave and, incorrectly, tidal
wave). Volcanic eruptions, submarine landslides, and coastal rock falls can also
generate tsunamis, as can a large meteorite impacting the ocean. These waves
may reach enormous dimensions and travel across entire ocean basins with little
loss of energy. They proceed as ordinary gravity waves with a typical period
between 10 and 60 minutes. Wave period is the time it takes two successive
waves to pass by. Their speed depends on the depth of the water. In the deep
ocean, tsunami waves propagate with a speed exceeding 1000 kilometers per
hour ([km], ~400-500 miles per hour).
The energy in a tsunami wave is spread out fairly evenly throughout the water
column. If a wave begins in the deep ocean, it may have a wave height of
several centimeters (1 foot [ft]) or less) and will not be detected by ships due to
its long wave period. Tsunami wavelengths are hundreds of times greater in size
when compared to ocean depth. Wavelength is the distance between two
consecutive waves.
Tsunami wave shape changes as it approaches shore because decreasing water
depth increases wave height and decreases wavelength.
Tsunami waves are distinguished from ordinary ocean waves by their great
wavelengths (often exceeding a 100 km or 60 miles [mi] or more in the deep
ocean), and by their longer wave periods (ranging from 10-60 minutes). As they
reach the shallow waters of the coast, the waves slow down and the water can
pile up into a wall of destruction tens of meters (30 ft) or more in height,
inundating low-lying areas. Waves can be amplified where a bay, harbor or
lagoon funnels the wave as it moves inland. Large tsunamis have been known to
rise over 30 meters (100 ft). Even a tsunami 3 to 6 meters (10-20 ft) high can be
very destructive and cause many deaths and injuries.
Tsunamis have no connection with tides; the popular name, tidal wave, is entirely
misleading.
Tsunami waves are often no taller than normal wind waves, such as surfing
waves, but they are much more dangerous. Tsunamis can flow inland for tens of
minutes while wind waves flow inland for tens of seconds. Tsunamis can create
strong currents. Therefore, even a small tsunami can be dangerous.
Subsections of this Article
| Pagename | Short title | Description | |
|---|---|---|---|
| Tsunami Science and Hazard | Tsunami Science and Hazard | Tsunami Science and Hazard | This page contains information on Tsunami Science and Hazard. |
Information about this article
Short title: Strengthening Tsunami Warning and Emergency Response
Description: This page contains information on Tsunami Warning and Emergency Response.
Expertise level: beginner
Author: Tammyfukuji
Approval status: approved
Approved by: Tammyfukuji
Last change: 2011-4-7
Subsection of: Tsunamis
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