Tsunamis can be deceptive. They are most often not taller than normal wind waves. But how dangerous they are is well known to all of us. They have been known to cause great destruction within minutes on shores. Some tsunamis can cause destruction across an entire ocean basin within hours.
 What Causes Tsunamis
The speed of tsunami is related to the depth of the water. Therefore, when it reaches the shore its speed diminishes but its height grows. Tsunamis are triggered by volcanic eruptions, landslides, earthquakes. They are also caused by undersea landslides and the collapse of oceanic islands into the sea.
It is also said that the impacts by comets or asteroids generate giant tsunamis, though such events have not been witnessed, except perhaps in films like DEEP IMPACT. Computer simulations show giant tsunamis swamp the Manhattan skyline, which makes us wonder whether they happened in the distant past.
 Tsunamis Are Difficult to Detect
As the heights of the waves can be as little as 12 to 23 inches, it is often very difficult to detect tsunamis. Such was the case when tsunami had struck Honshu, Japan, on June 15, 1896. Fishermen 20 miles into the sea failed to notice the wave under their boats as at the time it had heights of about 15 inches. They saw the devastation, in which 28,000 people were killed and 170 miles of coastline destroyed, only on reaching the port of Sanriku.
In deep water tsunamis can have a wavelength greater than 300 miles (500 kilometers). The ratio between a tsunami’s water depth and wavelength is very small. The deeper the water, the faster and shorter the wave is. For example, when the ocean is 20,000 feet deep, a tsunami travels at 550 miles per hour.
Also, because a wave loses energy at a rate inversely related to its wavelength, tsunamis can travel at high speeds for a long period of time and lose very little energy in the process.
 Tsunami Warning Systems
There is no way we can stop a tsunami. But there are several ways to avoid getting killed by one. The Japanese Government has built concrete sea walls and gates for protection against tsunami attack. Japan and the United States also have the seismometer tsunami warnings systems which come into effect when a large, shallow earthquake is detected under the ocean. But since not every earthquake necessarily triggers a tsunami, this method is plagued by false alarms. This can be seen from the fact that about 75 percent of the warnings at the Hawaii's Pacific Tsunami Warning Center had been false alarms which were followed by unnecessary costly evacuations.
To overcome this problem Japan installed a series of such bottom-pressure sensors along a cable stretching out from its coastline to detect a tsunami. The United States too have added bottom sensors to its warning system which relays the message to shore via satellite.
Considering the unpredictability of the warning systems, it appears that running for our lives remains as the best option. But there is a plan in place for that too. The tsunami-plagued regions have computer-simulated tsunamis enabling them to predict how high the tsunami waves will be and how far inland they will reach. These can help plan evacuation routes.
 Some Remarkable Rescue Operations to Inspire Us
1994 – When thousands were dying and many more were stranded on the islands in the Indian Ocean with all phone links snapped, Prasad, one of the 20,000 Indian ham radio operators, used her radio to contact mainland (India) and give information about those stranded in Port Blair
1994 - Many sex workers in Phuket Island, Thailand, who come from impoverished families, threw themselves into rescue work, and with their knowledge of English helped local officials communicate with stranded tourists.
Read first hand account of a brave lady and her son who helped save 50 lives.
 Health Effects of Tsunamis
Immediate health concerns
- Lack of clean drinking water, availability of food, shelter, and medical care for injuries are of immediate concern
- Flood waters can result in contaminated water and food supplies.
- Vulnerability to insect exposure, heat, and other environmental hazards increase
- After deaths the next major cause for concern are traumatic injuries.
- Medical care is critical in areas where little medical care exists.
- Contaminated water and food supplies as well as the lack of shelter and medical care can aggravate illnesses
- Decaying bodies create very little risk of major disease outbreaks.
- Those who handle the bodies or prepare them for burial are most at risk
 How Animals Survive
Following the 1994 tsunami it was discovered that no animal corpse was found at Sri Lanka's national wildlife park at Yala, which houses elephants, buffalo, monkeys, and wild cats. Yet there was widespread human devastation at the same venue with only 30 of the 250 tourist vehicles which entered the park returning safely to base.
It can be assumed that the animals had sensed the oncoming tsunami and had fled to safety. It is possible the animals may have sensed the earthquake before the tsunami hit the land
 Tsunami Dos and Don’ts'
- If you are in a dangerous area, immediately turn off the water, gas, and electricity and quickly move to a higher ground. Remember, once a tsunami warning is issued, it could be a matter of minutes, or even seconds, before the wave hits.
- If a tsunami warning is issued, never go down to the beach to watch the waves come in. Remember also that a tsunami is a series of waves. Often the first wave may be the least dangerous. The waves may get progressively worse. Listen to a portable radio to learn when it is safe to return home.
- After a tsunami has hit, all food and water should be tested for contamination before they are eaten. All buildings should be checked for gas leaks and electrical shorts before anyone enters. Administer first aid only if you know what to do.
- Stay tuned to local radio and TV stations for evacuation orders if a tsunami warning has been issued. Do not return to low-lying areas until the tsunami threat has passed and the "all clear" is announced.
Safety Precautions at the Coast
All sea areas are potentially at risk and whenever you are at the coast, you must realize that a tsunami could endanger your life and those of the people travelling with you.
- Always keep your mobile telephone with you.
Check from time to time that your telephone is actually logged on to a GSM network. You should do this in particular before you go to sleep. In areas with weak network coverage you may discover that you do not always have network signals at all points within your room. In such an event it could be helpful to move the telephone a few meters or to put it on a window sill.
- Act immediately when you receive an alarm.
Based on the tsunami alarm message, check whether you are in the region of the tsunami. If this is the case, immediately warn other people who are with you, as well as those around you. If you are not in the danger zone, think whether you know someone who is living or traveling in the danger zone. Try to reach and alert these people by telephone.
 Did you know?
- The 2004 tsunami in the Indian Ocean created waves as high as an eight storey building, but the waves of the tsunami at Lituya Bay in Alaska in 1958 was 45 times higher – almost 1700 feet
- When a tsunami struck 12 countries and left an estimated 150,000 dead and 5 million homeless, a lot of Americans had never heard of the violent natural disaster
- An earthquake in Chile can send a tsunami to Hawaii in ten hours, to Japan in twenty-four
- Catching a Tsunami in the Act
 Additional Information
- Tsunami Attack
- Tsunami destruction
- Learn more from Family Disaster Plan so that you can plan you evacuation in the event of a tsunami.
- See Asteroids & Tsunamis
- See a volcanic eruption which caused a tsunami in Indonesia in 1883 killing 36,000 people
- Tsunami warning systems
- Take a visual tour of survivors of tsunami at - Surviving a Tsunami—Lessons from Chile, Hawaii, and Japan
- Visit Tsunami Visualizations. Find animations and movies about recent and historical tsunami episodes