Tsunamis

[tagryn]

Tsunamis have been a compelling interest for me since I was very young. The waves
from the 9.0 Sumatra quake have caught the world's attention, as they should for
such a devastating disaster. I think others have covered the main points, so I'll
just offer a few additional observations/thoughts:

- Via Michael Totten's blog, here's a collection of eyewitness accounts from various SE Asia blogs

- I found the accounts of survivors who were scuba-diving at the time of the tsunami educational. I had always been of the opinion that anyone underwater when a tsunami went by would be hurt or killed by the concussion of the pressure wave going by, but apparently that was not the case. Still, there were many other incidents of divers who were swept out to sea and presumed lost, so the survivors' tales should probably be considered just good luck on their part.

- I remain convinced that one cannot surf a tsunami, "Lucifer's Hammer" notwithstanding. From the film I've seen of the tsunami, it isn't a wave per se but more of a sudden, massive increase in the water level. I recall seeing video of a stormchaser who filmed in front of a typhoon's storm surge, and that is pretty much what it was like: a series of rapid floods which didn't recede. Now, it is possible that video was only available for spots where the wave wasn't at full-force, and that anyone filming where the tsunami hit 30+ feet didn't live to tell the tale. However, given the lack of any kind of wave-face, trying to surf the thing would seem well-on-impossible (and stupid to boot).

- There was some speculation that the U.S. base on Diego Garcia would have been inundated by the tsunami, but by various reports, it was unaffected.

- There's been some news reports that this is the most devastating disaster in history. According to Table 2 in this report, it has a long way to go, even for single-incident disasters: Yellow River flood in China, 1931, 3.7 million dead; Bangladeshi typhoon, Nov. 1970, 1 million dead; 1556 earthquake in China, 830,000 dead; etc.

- Long-term, one worry is that the devastation caused by the disaster may set the stage for revolution in those areas affected, if recovery isn't swift. One example of this happening is that after Krakatoa devastated much of Indonesia, the Dutch colonial authorities' slow reaction helped seed an Islamic fundamentalist revival in the region.

Comments

[jilara.livejournal.com]

A tsunami is best understood in terms of energy compression. In open ocean, the wave front is diffuse, but as it nears land, it becomes more and more compressed. The divers were probably in water deep enough that the tsunami was still fairly diffuse and was not accelerating and raising noticably. The point at which it becomes discernable as a wave, popping up out of the seabed, is when the depth of the water becomes half the period of the waveform, if memory serves (it's been 30 years). This is only the *surge,* which become higher and higher as the depth decreases. The curl and break of a wave has a lot to do with complex dynamics of drag and the geography of the bottom, where the drag makes the lower part of the wave move slower than the top. Hence you get shoals that surfers love, where regular surge waves suddenly pop up hugely and crest, then either develop a curve or sometimes disappear without having "broken" as they hit a different bottom morphology.

A tsunami is all that surge, and whether or not you get a crest depends on a lot of factors of hydrology. Conditions have to be ideal, or all you get is the waveform, the wavefront surge. You'd be more likely to ride it with a boogie board than surf it. However, if it was high enough and hit obstacles like houses, autos, trains, it could create enough dispairity to give you a crest, but you'd be surfing down the curl into god-knows-what of debris below... And you wouldn't have it maintain curl for very long.

[jilara.livejournal.com]

The nation of Myanmar, formerly Burma, has been steadfastly claiming only 90 deaths for days, now. But they are notoriously secretive, and would probably have great interest in keeping away human rights folks who would offer aid, if there were great casualties. After all, everything is just fine in Myanmar, no matter what outsiders might believe. The government will be the first to say so. Meanwhile, everyone who looks at the tsunami models thinks they're covering up. It will be interesting to see what effect this has, long-term.

[tagryn]

You might want to check out this blog, it has the best compilation of links to videos of the tsunami I've found. The one titled "The most amazing tsunami video I've seen" is indeed that, point-blank from in front of the wave with roar included, the stuff of nightmares. Frankly, the fellow taking that is dead if the wave is a 100 foot monster, rather than the wave they got.

There's at least one report I've read of a survivor riding debris along another tsunami and surviving, but that's very much luck of the draw. I guess my reaction re: surfing tidal waves is prompted by those foolhardy souls who speak about their desire to "ride the wave" on a tsunami. They remind me of what Sitting Bull said about Custer: "They say I killed Custer. It is a lie. He was a fool and rode to his own death." Tsunamis are just a different creature from the kind of big swell waves they get off Hawaii.

[tagryn]

Something I've been noticing as I watch these videos is that in a lot of them, even if you knew what to look for in a tsunami, it'd be very hard to tell one from a "normal" big wave, at least from the ones caught on the movies. In one, the video taker was looking out at sea and could tell there was something strange going on because he was focusing on the disturbance as it approached land, but it just looked like a tide coming in rather than a wave per se - it wasn't until it hit land and kept coming in, and coming in, and coming in that it manifested itself. The "most amazing" video looked like a wave one might see at any surf break...except it occured in apparently still waters and swept inland much farther than one would expect a wave that size to do so (probably because it isn't a normal wave and has lots more kinetic energy behind it than tide waves or even storm swells).