'Merging Tsunami' Amplified Destruction In Japan 50
Hugh Pickens writes "The magnitude-9.0 Tohoku-Oki temblor, the fifth-most powerful quake ever recorded, triggered a tsunami that doubled in intensity over rugged ocean ridges, amplifying its destructive power at landfall, as seen in data from NASA and European radar satellites that captured at least two wave fronts that day, which merged to form a single, double-high wave far out at sea. This wave was capable of traveling long distances without losing power. Ocean ridges and undersea mountain chains pushed the waves together along certain directions from the tsunami's origin. 'It was a one-in-10-million chance that we were able to observe this double wave with satellites,' says study team member Y. Tony Song. 'Researchers have suspected for decades that such 'merging tsunamis' might have been responsible for the 1960 Chilean tsunami that killed about 200 people in Japan and Hawaii, but nobody had definitively observed a merging tsunami until now.' The study suggests scientists may be able to create maps that take into account all undersea topography, even sub-sea ridges and mountains far from shore to help scientists improve tsunami forecasts."
Re:Thinking through the uses... (Score:4, Insightful)
Here is a counterpoint [slashdot.org]. Risk management is not a one-time thing: if you are in a risky business (be is security, medical safety, nuclear power, etc.), you need to continually re-assess what risks exist and whether you have properly mitigated them. Failure to take new knowledge, such as improved tsunami science, into account as it becomes available and act on it appropriately is simply negligent.
conservation of energy (Score:5, Insightful)
What I find most interesting about tsunami is their ability to move energy so efficiently, with next to no loss. It's a wave traveling in a medium that has very little internal friction. This allows it to travel a tremendous distance without losing a lot of its energy.
The other thing is how it moves the energy when it's out in the ocean. Think of the tsunami when it's out in the middle of the ocean, and is generating a swell of say an inch. It's lifting a two mile column of water an inch up. That's a huge amount of energy.
When that wave approaches land, the distance from sea floor to sea level is much smaller, but the energy is mostly still there. So instead of raising it an inch, you get several meters. They refer to this as "coastal amplification" or something like that, but it's quite the nasty thing to pull when it hits landfall. If you were in a little skiff a few miles off the coast you may not even notice your boat rock, but if you were in that same boat a few hundred feet from the beach you'd be surfing in on a 25 meter high wave. What an amazing difference! It's no wonder Japan got yachts parked on streets a mile in from the coast.
Ocean floor topography plays a role in this too. And then you get effects like waves reflecting off entire continents and other large land masses, and opposite cases where little pockets here and there are sheltered from the effects due random luck involving coastal features. Tsunami are easily just as interesting a study as tornadoes or typhoons in their subtlety and power.