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Video of tsunami in Japan

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Re: Video of tsunami in Japan

#61

Post by anabis »

icegreentea wrote: post #40
ajays wrote: post #36

Color me educated. I used to think that a tsunami was a giant wave which would splash, and then it's gone. I didn't know/realize how slow-moving but MASSIVE this was. So what happens to all this water? Does it eventually go back into the sea the way it came in? Or is this the default sea-level now?

From the wiki article, by the time a large tsunami reaches the shore, it has a wavelength of ~20km, taking ~1-2 minutes to reach the peak of the wave. And yeah, in the long term, most of the water will go back out to sea (or evaporate off). Of course, areas that were below sea-level before hand, will now be big ponds until they're drained, but by and large, the water will withdraw (which does extra damage!).

> areas that were below sea-level before hand Some areas became below sea-level _after_ the quake. The land sank a maximum of 70cm.

Re: Video of tsunami in Japan

#62

Post by magicofpi »

ajays wrote: post #36

Color me educated. I used to think that a tsunami was a giant wave which would splash, and then it's gone. I didn't know/realize how slow-moving but MASSIVE this was. So what happens to all this water? Does it eventually go back into the sea the way it came in? Or is this the default sea-level now?

Yeah, I think a good number of people don't understand how tsunamis work, even here in Hawaii. During an emergency, radio and TV broadcasters here try to explain that tsunamis are more like solid walls of water - i.e. the entire ocean lifting up six feet, but of course, people don't listen. That makes it very dangerous when there's a tsunami warning (like last Thursday), because people think, oh, it's just like surfing! six feet is not even that much!, which means that some people don't evacuate. Plus there are always some geniuses that insist on sitting next to the shoreline, and the police have to shoo them away.

Re: Video of tsunami in Japan

#63

Post by SkyMarshal »

magicofpi wrote: post #62
ajays wrote: post #36

Color me educated. I used to think that a tsunami was a giant wave which would splash, and then it's gone. I didn't know/realize how slow-moving but MASSIVE this was. So what happens to all this water? Does it eventually go back into the sea the way it came in? Or is this the default sea-level now?

Yeah, I think a good number of people don't understand how tsunamis work, even here in Hawaii. During an emergency, radio and TV broadcasters here try to explain that tsunamis are more like solid walls of water - i.e. the entire ocean lifting up six feet, but of course, people don't listen. That makes it very dangerous when there's a tsunami warning (like last Thursday), because people think, oh, it's just like surfi…

Even "wall of water" is misleading, as that's not what it is at all. A horizontal wall perhaps, but not a vertical one like in the finale of Abyss.

One way I've used to explain it is to imagine you're on a boat at sea and a tsunami passes under you. You wouldn't even notice.

The boat would slowly rise a few feet and stay there for a few minutes as this huge mass of water passed under it, then slowly drop back down to its original height, and no one would be the wiser.

It's not until the mass of water hits the shore and keeps piling on for several minutes, that people can see what it is.

Re: Video of tsunami in Japan

#64

Post by brazzy »

btilly wrote: post #43
pokjhnboi wrote: post #30

Earlier quoted context omitted.

They didn't forget - a Tsunami is a block of water a meter high and several km deep moving at 800km/h. That's a few BILLION tons of water moving at the speed of a jet aircraft - try designing against that.

Important first correction. The wave moves at that speed. The water itself does not. It mostly bobs up and down slightly. Important second correction. The height of the tsunami when it hits shore is not the height of the tsunami when it is out at sea. All waves, tsunamis included, rise up when the bottom of the water starts to compress the bottom of the wave, compressing its energy into a smaller volume. With these c…

There actually were such dikes in some places, you can see them overflowing in some of the videos.

The thing is, you have to decide how high a dike you're willing to pay for, which is a cost vs. remaining risk tradeoff. The risk of the 5th strongest quake ever recorded occuring right before your piece of the coast was apparently considered acceptable - Hindsight always wins.

Re: Video of tsunami in Japan

#65

Post by khafra »

pokjhnboi wrote: post #27
rubashov wrote: post #26

What was wrong with the term "Tidal Wave"? It looks like a huge tide rolling in.

They are nothing to do with tides. Tsunami means harbor wave which is a good description - at sea they are almost unnoticeable - it'sonly when the water is concentrated on a shore - or in a harbor that they have such an effect

I think Rubashov understands that the process generating these waves is nothing like that which generates the tides, but correctly observes that the process resembles a tide--huge volumes of water rising, then falling back into the sea--more closely than ordinary waves, no matter their size.

Re: Video of tsunami in Japan

#66

Post by salemh »

salemh wrote: post #53
skeletonjelly wrote: post #9

Earlier quoted context omitted.

To be fair, theres nothing of nature's that stands in nature's way. It ruins it's own shit too. It's all entropy right?

Can't find the source from months back, but, us humans were constantly trying to stop all forest fires in near-populated area's, which were needed (by nature) to clear area's for other vegetation which can't grow in certain over abundances of tree species.

Was that too simplified? Sources. Basically, soil enrichment, the "choking" of other plant vegetation if fires do not occur at intervals, etc. Its the same argument of overpopulation of deers = starvation of deers, since we've taken out the natural predators of wolves in many area's, hunting is a necessity.

http://www.springerlink.com/content/q8755xw004285060/ http://www.enviroliteracy.org/article.php/46.html

http://www.infoplease.com/spot/forestfire1.html "Forest fires can have beneficial effects. Charcoal enriches soil, and some plant species flourish in the wake of conflagrations. The cones of the jack pine tree, for instance, will not release their seeds unless exposed to intense heat. Sequoia or Douglas fir trees grow best in open sunlight areas, such as those cleared by fire.

Natural fires also remove dead wood and tangled brush. For these reasons, the Forest Service of the U.S. Department of Agriculture, which administers 17% of all U.S. forest reserves, often allows fires, especially when started by lightning, to burn in carefully monitored areas."

Edit: The Parent (up deus) post stated "Nature ruins its own shit right?" not necessarily if you look at the world as an entire ecosystem. I guess I am confused as to its upvotes, when it means absolutely nothing.

Re: Video of tsunami in Japan

#67

Post by pokjhnboi »

btilly wrote: post #43
pokjhnboi wrote: post #30

Earlier quoted context omitted.

They didn't forget - a Tsunami is a block of water a meter high and several km deep moving at 800km/h. That's a few BILLION tons of water moving at the speed of a jet aircraft - try designing against that.

Important first correction. The wave moves at that speed. The water itself does not. It mostly bobs up and down slightly. Important second correction. The height of the tsunami when it hits shore is not the height of the tsunami when it is out at sea. All waves, tsunamis included, rise up when the bottom of the water starts to compress the bottom of the wave, compressing its energy into a smaller volume. With these c…

Thanks - I was trying to get across that this is a block of water the mass of a small mountain dropping on you. You can earthquake proof a building but you can't do much against this.

Even a regular storm surge in the north sea needs some serious mega-project engineering to protect a single river/city. Protecting the entire coastline of Japan against a Tsunami would be tricky

Re: Video of tsunami in Japan

#69

Post by skeletonjelly »

skeletonjelly wrote: post #9
51Cards wrote: post #5

And somehow we think we are masters of the planet. When nature's true forces come to bear there isn't much we have ever built that stands in the way. Here's to wishing all those that survived a speedy recovery and my condolences to those who know people who didn't make it.

To be fair, theres nothing of nature's that stands in nature's way. It ruins it's own shit too. It's all entropy right?

Holy shit there comes an s!
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