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Author Topic: Why aren't tsunamis even?  (Read 4892 times)

Offline Eric A. Taylor

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Why aren't tsunamis even?
« on: 12/03/2011 01:32:41 »
While watching coverage of the tsunami that hit the Oregon coast this morning they showed a graphic the showed the (I assume) predicted energy of the tsunami over the entire Pacific. The graph showed the greatest energy at and around Japan, of course, but there were fingers of grater energy extending across the ocean. I know the topography of the seabed has something to do with this, along with the shape of the coast, I'm wondering why this pattern happens, almost like rivers. Do the ocean currents have anything to do with it?

In a related subject, watching the coverage on TV I saw several people walking around the beach. Fortunately the tsunami was small here. There was a death in Crescent City, which is in Northern California, but until the wave arrives we don't really know how big it will be. Even a 2 or 3 foot tsunami is big enough to knock you down and drag you out to sea. Despite this, people were still out there. Why are some people so STUPID!!?


 

Offline SeanB

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Why aren't tsunamis even?
« Reply #1 on: 12/03/2011 13:35:34 »
Noone ever has overestimated stupidity............

The reason for the varying heights is because the sea floor is not flat and level, but has a topography very much like the continents, with deep spots, shallows and canyons and the top of the mountain ranges sticking out on top of the water. This affects the amount of energy at the various locations as the original wave gets variously reflected and diffracted on the way. As well the tide has an effect, if it will be high tide at the location when the wave arrives, even a small wave can do considerable damage, whilst if it is low tide the wave has to be at least the tidal height before it has any effect. Remember that there is a trough before the wave arrives, and this can cause problems if people go out into previously covered areas when the water retreats before it comes back with considerable force.
 

Offline Donnah

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Why aren't tsunamis even?
« Reply #2 on: 16/03/2011 18:43:32 »
In a related subject, watching the coverage on TV I saw several people walking around the beach. Fortunately the tsunami was small here. There was a death in Crescent City, which is in Northern California, but until the wave arrives we don't really know how big it will be. Even a 2 or 3 foot tsunami is big enough to knock you down and drag you out to sea. Despite this, people were still out there. Why are some people so STUPID!!?

It must be natural selection, they'd have to do something more original to be competing for a Darwin Award.
 

Offline CliffordK

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Why aren't tsunamis even?
« Reply #3 on: 17/03/2011 19:58:14 »
I was thinking it might be good to head to the beach.

When we have 7 foot tides.
A 3 foot Tsunami would hardly inundate much (except at high tide).

The problem would be if one was caught off guard, or in a place where one's movement was restricted.

However, it would be spectacular to watch the wave crashing against the rocks.
 

Offline SeanB

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Why aren't tsunamis even?
« Reply #4 on: 18/03/2011 19:24:13 »
The last Tsunami that hit here was 5 cm or so high after crossing the Indian ocean. It disappeared into the tide.
 

Offline CliffordK

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Why aren't tsunamis even?
« Reply #5 on: 19/03/2011 06:36:13 »
It sounds as if there was some "real damage" in Crescent City, California.

http://www.usatoday.com/news/nation/2011-03-11-california-tsunami_N.htm
http://www.heraldandnews.com/breaking/article_a7ff6916-4bf1-11e0-ab85-001cc4c002e0.html



As I understand it, these big boats are much safer out at sea than in the harbor.  And there should have been adequate warning to get them away from the docks.

In Hawaii, there are notes of US Subs breaking from their moorings.  If they had gotten them out to sea, there would have been no risk to them.
 

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Why aren't tsunamis even?
« Reply #5 on: 19/03/2011 06:36:13 »

 

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