the only way the wave could be reduced would be the construction of the equivalent of the Great Barrier Reef to dissipate the energy held in this huge volume of water - or open up a void for it to fall into! - or we could detonate huge depth charges to reduce the column of water to spray ( probably not)

Thanks Andreas. What about creating an artificial land sliding oppoist the Tsunami wave?

Thanks Haider

. Intersting link.

Thanks John. Some good ideas.

This occur without pre information since it is a natural phenomenon.Never the less the occurence or effect could be prevented or minimized through net work of monitoring systems,early warning systems establishment of data gathering and funding and encouragement of research activities for such specific events

From my point of view, we need many factors to simulate Tsunami wave than we can find solution for this problem. One of this factor as Gobo A.E. mentioned above, also we need to know how many cycle per each period for example 10 years that happened and also the height of the wave when it attach the land. When we study deeply all factors then we can find solution such as we can made some gates in front of the coast lying horizontal in water when the level of water increase more then the normal this gate change its position to the vertical to crash the wave height and to reduce the damage on the land behind it.        

Thanks Gobo

Thanks Mohamed

The idea of  neutralizing tsunami wave by interference is good but think of the energy released during a large earthquake that triggered a tsunami. To counter that force you need energy more than what is released during the earthquake.

Thanks Devojit

How about selective paths for water? Most cities have quite the volume of underground infrastructure such as sewers. It's hard to counter a big wave(s) but it's much easier to build a system of doors to let water run free in selective parts of a city infrastructure. With a digitally monitored system of doors it would be possible, even if the sewers fill completely, to select specific surface parts for the water to go to. This way even evacuation and shelter plans would be much easier to plan and execute since the police would know exactly in what areas it would have to intervene in the imediate. Evidently this is not "exactly" preventing a tsunami but to choose where it's force will disseminate to. But it seems feasible and durable and actually functional to any other water related incidents. The draw back would be the need for maintenance since its mechanical. 

Thanks Pedro, Yes , this is a good idea to propose for large cities such as New York and in Japan or Indonesia.

This has been a wide ranging discussion of a deadly natural phenomenon. I was on the American Institute of Architects study team as the representative of the Am Soc of Civil Engineers during the May 2005 visit to Sri Lanka. From wave theory we know we can cancel waves, especially sound waves--Bose and other manufacturers offer nice headsets for noisy airplanes. But practically we do not command the energy to generate and control counter waves. If we generated a counter wave that was not well tuned there is a real chance the huge wave generated could compound the death and destruction locally and on the backside of the tsunami source. Triggering a landslide without exact control of how much mass and the timing of the entrance into the water is much more likely to cause local death and destruction and increase death and destruction on the back side of the original wave source hours after the initial waves hit. The December 2004 South Asian earthquake was reported to have had the energy to decrease the diameter of the earth by 1-2 inches or a cm.

In tsunami disaster management, there are two classes of unknowns that hamper responses--the wave generation and the receiving shore line topography that controls wash-up and how far inland the wave moves. In the Pacific we have minimal deep-water buoy coverage to know the number of waves coming but much hind casting is necessary to estimate the wave amplitudes and timing and this comes long after we would need the timing and amplitudes to counter the waves. 

In Dec 2004 we picked up the cm high waves in deep waters by satellite radar but this was happenstance that was noted after the damage was done.

Filling the sewers and other open spaces are also counterproductive. Great energy moves huge volumes of water. especially compared to typical sewer volumes. The sewers and other open spaces will fill naturally despite flap and other type gates that prevent back-flows. In Galle the old Portuguese fortress was almost over topped by the waves but was rendered uninhabitable by the sewage pushed into the fortress and some drowning occurred as I recall. Many lives were lost in the Galle soccer stadium where some of the local population sought shelter because of the sewer and drainage back flows caused drowning.

The comment about the Great Barrier Reef was well taken and consistent with the extensive experience in Japan with smaller wave dissipation and control. Around the coast of Sri Lanka reef mining for construction aggregate seem to open the coast near cities and towns to greater devastation. The steeper offshore morphology is, the better wave mass and energy reflection are. The west coast of Sri Lanka was actually hit by waves reflected from India after dissipation from 30 feet or 10 m high to 3 feet or 1 m in wash up height.

I hope we think of some solution in these wide ranging discussions. The Minoan civilization in the eastern Mediterranean was wiped out by a volcanic eruption. Approaching half of the US population is at risk from 100 foot or 30 plus m tsunamis from potential landslides in the Canary Islands that also threaten Brazil, the Caribbean, the Bahamas, Europe and Africa. Paleo records indicate the Arabian coast has been devastated before as has the US Pacific northwest. Oceanic strikes of meteors are very difficult to project and prepare for.

I love the seacoast; but I live 100s of km inland, primarily due to the risk of hurricane surges.

Thanks Steven for the valuable information

Considering countermeasures in response to tsunamis is definitely outside my field of expertise; however ideas generated from those outside the normal realm of thinking can sometimes turn into feasible solutions. Approaches to tsunamis should no longer be reactionary; after all of the death and destruction caused by tsunamis, they should be planned events.

It is my understanding that tsunamis are generated by earthquakes, volcanic eruptions, underwater and above water landslides, and anything else (man-made or natural) that can disrupt the flow of ocean waves in a massive way. Seems to me with all of the advances in technology that as soon as one of these catalyst events occur, it is inevitable that tsunamis will develop. These events keep happening in the same region, to me it is feasible to plan countermeasures ahead of time.

My theory posits that multiple sonic boom generators (containing analytic components) can be installed on ocean floors in regions predisposed to tsunamis. Tsunamis can travel at 500 mph and can be 100 miles in breadth, and can reach 30 ft. in height. Efforts to neutralize waves must be immediate to have any chance of impacting strength of waves. One sonic boom generator does not seem feasible to me, one generator would only have a potential impact on a minuscule part of a tsunami. Tsunamis are massive, they require massive countermeasure efforts.

These generators can generate sonic waves in ascending manner that build up in intensity in increments. The worst thing to do is to set off huge sonic booms that can actually create worse problems than the original tsunami. Overkill can create a reverse tsunami that can travel back to area of origin and add to destruction already experienced from catalyst event. These sonic boom generators (if they can be developed) could be placed close to known catalyst locations (ex. starting next to active volcanoes, close to known earthquake epicenters, etc.) and be placed in intervals all the way to vulnerable coasts. My idea is to be aggressive from the start, but not so aggressive that efforts create worse problems. Sonic boom generators that are located the farthest from the coast can send out sonic waves to chip away at the tsunami as it travels. As a tsunami travels, the properties of the wave would have to be analyzed to determine whether efforts have indeed decreased the potential impact on destined coast. If at a particular point, the tsunami has not decreased enough in intensity, further sonic wave efforts would continue. I can appreciate that my thinking can be viewed as rudimentary, please remember that I am a complete novice and the laws of physics and engineering capabilities do not limit possibilities in my thinking. 

the sonic boom generators are a very great idea. but what if we use the wave's energy to our advantage and powered the generators based on the energy of the wave.

im just a student so i dont have much scientific knowledge but i have many ideas, 

One idea is to measure the rise of the plate boundaries over time to help measure the impact of the earthquake when it snaps back in place.  the longer the pressure builds up the higher the plate boundary would rise until the tension couldn't hold its grip.  

According to a student of mine, the tsunami can be weakened or neutralized by "air bubbles". He experimented the method with good results.

All you need is a long pipe near shore. Blow air which can be released in holes along its length the moment the wave arrives (or continuously).

I think that it is impossible to prevent a tsunami, but one can have early warning systems that can at least help to mitigate the impact of long-distance tsunamis. An important activity is also creating awareness about the indications of tsunamis. If one is in a coastal region, experiences an earthquake which is so strong that one cannot remain standing then it is the best to get quickly to higher ground. Even if later it turns out that no tsunami happened it was worth doing this precaution. For long distance tsunamis there is usually sufficient time to warn distant locations to be affected, but as the 2004 tsunami in the Indian Ocean shows several hours that the tsunami needed to reach India and Sri Lanka was not long enough to prevent tens of thousands of victims.

Thank you Eberhard. The idea of air bubbles suggested by Michael sounds good and need to be experimented at large scale!

Once a tsunami has been formed, there is no way to stop it; but with an effective warning system in place, people can be evacuated.

And reducing the damage caused by a tsunami is certainly achievable. Tsunami walls, flood gates, and channels are three measures that can be taken to that end.

Japan is prone to tsunamis and has built numerous tsunami walls along the coast of heavily populated areas. The tsunami walls are designed to absorb some of the energy of the tsunami and redirect some of the water back towards the open ocean. The walls may be as high as 14 feet (see picture below).

Flood gates and channels can help redirect some of the incoming water from a tsunami, but a large tsunami will easily overwhelm any of the measures that are used to reduce its strength.

In an International Conference on Geo-Engineering and Climate Change, 2015 held in MNNIT, Allahabad, a Japanese researcher has suggested the use of old cars/ truck tyres placed at an angle of 30° -45° at the banks in order to reduce the impact of tsunami.

I think that prevention is not possible, but one can protect better (e.g. settle in higher locations) , prepare better (have early warning, know how to read the signs of an approaching tsunami), and have better post-tsunami management.

Thanks Eberhard.

I think there are many ideas to prevent tsunami waves hit lands. One of these ideas is build walls in coastal to be in horizontal position when ocean wave is normal. However, when ocean water level reduces due to tide and earthquakes. Thus, these walls/sheets become in vertical position. Then, these walls break the wave length and reduce the damage of tsunami.