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 As the world comes to grip with the full impact of the recent tsunami in Japan, AWT offers its condolences to those families who lost loved ones, and offers our prayers and concerns for the country of Japan and for those who are suffering and displaced. In the wake of such a disaster, it is not unusual to ponder how and why such an enormous event can occur with short warning and little or no ability to minimize its destructive power.
Mike O’Brien, Senior Operations Manager, provides "Tsunamis: A Look Inside" in this issue of AWT Insights. In this article, Mike discusses the cause of tsunamis and presents practical information on dealing with them.
Enjoy your reading. We welcome your feedback.
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Skip Vaccarello |
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| Tsunamis: A Look Inside |
| by Mike O’Brien, Senior Operations Manager |
 In light of the recent events in Japan, AWT thought it would be prudent in this issue of AWT Insights to take a closer look at tsunamis and examine their warning systems. While it is clear that the tsunami in Japan has had a profound effect on many aspects of life, we would like to focus on our area of expertise: shipping.
What is a Tsunami?
The word tsunami is derived from two Japanese words: tsu (port) + nami (wave) – reflective of a culture long suffering from these destructive waves. The result of an underwater disruption, tsunamis are most frequently caused by underwater earthquakes, but can also be the result of undersea volcanic activity or landslides. Such an occurrence initiates a wave with an extremely long wave length and small amplitude, moving with speeds up to 500 knots. As the tsunami eventually encounters shallow water, it slows down, forcing water to ‘pile up’, which creates the destruction that we see pushing ashore with such overwhelming power.
Interestingly, as destructive as these waves are ashore, they are unnoticed by ships in deep water. With wave lengths in the range of 270 nautical miles (NM), and wave heights of just two to three feet, a tsunami wave in open water does not vary significantly enough from normal wave patterns to cause alarm.
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Receding Waters Provide Natural Tsunami Warning
One of the signature warnings of an approaching tsunami is the receding waters along the coast. This happens when the trough of the tsunami reaches the coastal waters. The deepening trough as the wave slows results in a dramatic receding of water, leaving boats in the mud and marine life exposed. The extent to which water recedes will vary depending on the wavelength of the tsunami and at which point in the wave form it came ashore. In any event, this should be an absolute warning to abandon coastal areas for high ground immediately.
Scientific Warning Systems
In recent years, we have turned to science to supplement the natural warning tsunamis may provide. A network of seismic measuring devices scans the world for earthquakes and other disruptions which may cause tsunamis. Once such an event is noticed, the intensity of the disruption – along with the location and other details – is analyzed and official tsunami warnings issued if criteria are met.
The agency at the forefront of these warnings is the Pacific Tsunami Warning Center, located in Hawaii. Following the disastrous Indonesian tsunami, the agency has expanded its reach from the Pacific Ocean basin to a more global scope. While the Pacific Tsunami Warning Center has done a fantastic job alerting people to tsunami risks, there are limitations far beyond their control. One such limitation is the proximity of a major earthquake to the shore, similar to the recent Japanese tsunami. Because the immense earthquake was so close to land, the resulting tsunami took just 20-25 minutes to reach the coast. Unless word is received directly from the reporting agency there is simply no time to react.
Be Informed
AWT believes that the most effective way to stay informed of these events is to get the information directly from the Tsunami Warning Center at the moment a warning is issued. For those interested in receiving immediate email notification messages from the Pacific Tsunami Warning Center, please see below:
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Visit the Tsunami Warning Center. |
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On the left menu under the Messages heading, click Subscribe. |
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Under the Email heading, click the link for PTWC Tsunami alerts and updates by email. |
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You will be directed to a signup page where you can enter your desired email address. |
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The next page will ask you to confirm your email address, and then hit submit. |
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You will need to confirm your subscription by viewing your email that you signed up. |
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Once confirmed go here. |
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Enter your email and select the Tsunami check box then click submit. |
Please note that AWT has no affiliation with the Pacific Tsunami Warning Center; a branch of the National Oceanic and Atmospheric Administration (NOAA) in the USA. Rather, it is AWT’s intention to keep marine interests informed and educated in advance of such events to help minimize impact and damage.
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