tsunami and Aldabra


Larval Mass
Thanks Scott! I finally got an answer from one of the researchers down there. It is very short but the only one I got. Here it goes:

"I am pleased to say that from what I have heard the tsunami did absolutely no damage to Aldabra. I have just returned from diving at nearby islands and there was no evidence of any damage, and people living on the islands noticed nothing."

Now, that's good news but I don't quite understand how it can be. I have looked around quite a bit and nobody was able to give me a satisfactory explanation. The tsunami is said to have travelled at around 500mph in the open ocean and slow down and grow in shallower waters. The explanation that it was very flat and therfore went unnoticed in the open does not quite satisfy me. "Normal" ocean waves, even when only 5 feet tall, shake a boot quite a bit when met frontally. Hence I would imagine that a wave, never mind how flat, propagating at this speed should cause serious damage to most things in its path.
Any sources on tsunami propagation?



But your five-foot wave hits your boat pretty quickly. Since the wavelength is so long on the tsunami in the open ocean, the onset is very slow: if it takes 10's of minutes for the wave to pass, you don't notice it because its just slowly lifting up your boat and then lowering it again for those 10's of minutes. The wave doesn't have a "break" until it reaches shallow water.



Larval Mass
Thank you Dan! Your, otherwise not very clear explanation (note the"never mind how flat" in my posting - thus obviously no "break" :cry: ), contained the keyword - wavelength.
Tsunamis have a wavelength "in excess of 500 kilometers":


Hence, despite the huge speed of the actual wave the water in the open rises very slowly to reach its maximum height in the middle of the wave, and that (there you are right) can take over an hour.

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