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!).
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.
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.
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.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.
That doesn't cover any of the damage from the tsunami or radiation, which should both add quite a bit. The government's also on the hook for a lot of the damage to residential buildings (some of which we saw float by in the linked video).
I wonder if an artificial tsunami of the same scale can be achieved my setting off a nuclear bomb underwater? This seems to be more damaging (infrastructure-wise) than a direct nuke hit.
According to wikipedia scale an 8.8 magnitude earthquake has approximately the same energy release as a 288 megaton nuke. Since the largest nuclear bomb ever was 100 megaton and a 35km radius for the zone of total destruction, direct bombing is almost certainly more damaging.
I (morbidly) wonder if it would be possible to set off a tsunami with just the explosion, without necessarily the ground movement. It would seem to me that a lot of the earthquake's energy release would go into shaking the ground.
I like how the water level rises from the beginning to the end, at the start there's just a few cars moving a little and you're like "this isn't so bad", and then at the end water is gushing in with cars and buildings rolling around in a cacophony of madness, even the camera man has retreated to well above water level at this point.
My Firefox (3.6.13 on OS X) decided to overlay the video extending it outside the page bounds and covering the status bar, and it will not go away now that I closed the tab, remaining overlaid over all the other pages when I switch tabs.
I chuckled a bit when the parked cars started bobbing, then made their way to the 'street' and floated away as if driving off to work. Everything else was horrifying.
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.
It only becomes a visible problem in harbours (or otherwise in shallow waters).
It looks like a tidal wave in the sense that it's a lot of water moving in a given direction. The mechanism causing it is not the same at all, so the name tidal wave is misleading.
As an example a friend of mine was on a boat during the massive 2004 tsunami, but since he was a few miles off the coast where the water was deep he didn't even notice the tsunami sweeping under his boat. Once it hit land it did massive damage.
It's because the tsunami only becomes visible when it hits your harbors. They used to be called "tidal waves," but the term is inaccurate — that's why it isn't used anymore. They're not like normal waves out at sea, and they have nothing to do with the tides. The fact that it "looks like a big surge side rolling" in does not actually make it tidal.
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 corrections, a tsunami out at sea is a wave a few cm high moving at 800 km/h with the water barely moving, but with the whole water column moving. It is therefore entirely conceivable that a well-built dike could withstand such a wave.
Obviously such dikes were not in place this time, but the feasibility of building them has been investigated. By Japanese scientists no less. See http://www.pwri.go.jp/eng/ujnr/joint/37/paper/13kato.pdf for one paper on the topic.
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.
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
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?