I’m having trouble visualizing a 16" tsunami as reported to have hit Japan after the 8.1 quake off the coast.
Since they bother to report it I assume it’s not just a 16" wave that breaks at the shore (how would you distinguish it).
Is it a short “wall” of water that travels far inland?
Thanks.
A tsunami can be pretty small as it travels across the ocean at high speed (500mph), but when it hits land, the shallower water causes the shape of the wave to change, I believe it slows down but the wave size increases thus preserving the same amount of energy.
I assume it was bigger than 16" when it actually hit land.
No I believe they report the wave height at shore (like the nasty one in the Indian Ocean was several meters tall).
That’s why I’m curious about why its even reported if its just a little wave; unless it does go far inland.
Anyone in Japan out there? Help?
While the amplitude of a tsunami usually determines its destructive power, the wavelength is what makes a tsunami different to a regular wave. The waves that destroyed so much around the Indian Ocean, were something like 40 km (~24 miles) long when they hit the land.
A 40cm (16") tsunami isn’t going to cause much damage, thank goodness. But the very long wavelength of the tsunami means that, unlike a wind-generated wave that lasts a few seconds, that rise in water level is sustained - from 10 to 20 minutes in the case of the Indian Ocean tsunami, travelling an estimated 150km/h (~93mph). This means that because of the raised water level at the coast, the water will rush in to fill the parts of the land that it exceeds in height, for as long as it lasts.
Thus a 10 minute 16" rise in water level at the coast could actually cause a bit of disruption, and possibly minor flooding in areas that are very close to sea level.
The “wall of water” effect is determined by the velocity of the wave - how fast the water in the middle of the wave is catching up on the water at the front - as it hits shallower water.
Tsunami’s a low frequency wave, so at shore it appears as a rapid 16" rise in sea level, rather than a normal wave. Sort of like a tidal bore (vid)
HA! 16" all of a sudden can do a lot of damage. Let me take you for a tour of the 9th ward in N.O. We’ve still got cars stacked everywhere. A short wave but moveing quickly hitting all of a sudden with the force of the ocean behind it can kick your arse.
16" high has no bearing on how long the wave of water is. If it’s a few miles “deep” the damage could be significant.
I’d say this was a whoosh, but as a guest you may not know what that meant.
New Orleans was drowned by water breaking through a levee. No waves of any size, shape, or duration were involved.
I think I know what you mean - that moving water can do damage to anything that gets swept up in it - but you’re applying that fact in the wrong thread.
Is this the event you’re talking about? I don’t watch much news, so I didn’t pick this up before. There was probably more coverage of past events than the current one. Doesn’t seem to have been a big thing as no one mentioned it at work today. When I looked it up on the Japan Times site there was a much longer article on the 1993 tsunami that hit Okushiri-jima.
What broke the levées though?
I had some trouble keeping up with/making sense of the reports coming out of NO during and just after Katrina hit, but my impression was that it was a storm surge having been brought up the Mississippi distributaries and then hitting NO “from behind” as it were.
In which case the analogy would be quite sound, I think: an SSW is effectively a surge, a local rise in the overall water level, as is the storm surge associated with a hurricane. Because it is not just a wave that hits, breaks, and stops in the sense of what one sees at the oceanside, but rather something that immerses and keeps on doing so, the effect is out of proportion to the apparent height measurement. The fact that on certain shoreline configurations, a SSW is forced into “breaker” mode and turns into the Hokusai-esque “tidal wave,” obscures the basic fact that it is a surge. While “tidal wave” was a misnomer for a SSW, it did carry the useful bit of data that the effect is more akin to a tidal bore than it is to a normal ocean wave.
I expect that it was widely reported because there was originally a tsunami warning with the potential for a several meter high wave. When it hit, the wave was, fortunately, the relatively small 40cm wave that occurred, but since there was the widely-reported major warning, the mimimal result was newsworthy.
I heard it hit a Spinal Tap show, smashing the 30" Stonehenge.