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When Isla De La Palma sends 200ft waves towards NYC, turn on yer nuke-powered air pumps, and pressurize the giant seabed array of perforated concrete pipes. Or, if you took the low bid contract, then instead you must release the billions of air-filled rubber duckys from their sea floor boxes at just
the right instant before the tsunami arrives.
The speed of tsunami waves is ~ few hundred MPH, while the wave-speed within dense foam is much slower. If gravity waves encounter a deep region of foam, they should reflect/refract upon encountering such a mismatched impedance. We can increase the reflectivity to near 100% by using multiple parallel bubble curtains of approximately 4 X Lambda thickness: an Interference or Bragg reflector. Build a collection of submerged air pipes spanning a few thousand miles, in a region a few miles thick. Or for less cost build a bubble-foam fresnel prism which bends the tsunami so it travels parallel to the coastline, and we should be able to save the coastal cities from destruction.
(Hmmm. Small oversight of the Mad Scientist kind: when first turned on, the bubble-maker could generate a tsunami far worse than the one being reflected. Oops.)
(Hmmm^2. A curved array would concentrate the reflected tsunami to a distant focus. And if the air pumps were slowly pulsed, they might *launch* a focused tsunami, w/no earthquakes needed. For entertainment, first carve yourself a large surfboard from a piece of the Antarctic ice shelf. Or, perhaps bore a canal through Africa? So ships can save fuel and don't have to go 'around the horn?')
Periodic array prevents optical wave propagation [wbeaty, Sep 11 2009]
lol, odd coincidence
Nuke Cumbre Vieja (also called ...Isla De La Palma!) [wbeaty, Sep 11 2009]
||Ah, the tiny inexpensive version: NYC protects itself by aiming the wave at New Jersey.
||Bubble breakwaters were proposed for the Mulberry harbours in 1943, but were judged not to be feasable due to the enormous power demands.
||//...the bubble-maker could generate a tsunami far worse than the one being reflected. Oops.// That would be what [bristolz] would have called a "neener neener neener moment". [+]