I read a story linked at Drudge to Ireland Online at http://breakingnews.iol.ie/news/story.asp?j=102381226&p=yxz38y788 about a surfer in the Maldives named Mike Riggs who supposedly surfed the tsunami. He said that it was only about three foot high where he was (he was engaged in surfing already). Is this possible? I know that the wave grows as it approaches the continental shelf, but I would think that the sheer water speeds of hundreds of miles per hour would make this virtually impossible.
While we are on the subject what would happen to a boat in the path of such a wave? Could it “ride out” the wave or would it go the way of the boat depicted in The Perfect Storm. Let’s say I’m on my dream fifty foot cabin cruiser and I get a report that I’m three hundred miles or about an hour in front of a tidal wave (and I’m many hours from shore). Which of the following would be a rational choice:
a. Turn my boat into the wave as depicted in the above referenced movie.
b. Head away from the wave towards shore.
c. Head at some angle into the wave or laterally.
d. Break out the rum have sex with anyone available and get ready to enjoy my last action adventure.
Finally, could we one day “cancel” out tsunami’s over a small area by creating counter waves? I know that the energies involved in creating these waves are equal to millions of atom bombs, but consider the following factors:
a. The energy transfer efficiency in creating a wave from an earthquake is probably relatively low. We could probably do much better with proper demolition engineering.
b. While the wave spreads out over many, many miles we would be concentrating on disrupting only those parts which were in front of populated areas a tiny fraction of the total wave area.
c. I’m thinking of very large non radioactive explosions involving tens of thousands of pounds of the highest grade C-4 type explosives positioned ten to twenty miles from shore in front of key, high risk cities (such as certain ones on the Eastern Seaboard of the United States which might be threatened by a Canary Islands type event). We might even consider a string of ten megaton H-bombs (I don’t think that we have them that big, but the Russians used to I think) positioned about one hundred and fifty miles off shore at key locations to counter such an event.
The mass water displacements created by a sea-quake mostly happen deep below the surface. The spectacular waves happen when the displaced water, moving at many hundreds of mph, reaches a shallow shore and is forced upwards, above the normal waterline. When you are at sea, far away from shore, you would barely notice anything unusual as the water passes below you.
So, (a) probably wouldn’t hurt, just to be sure, and (d) is always a good idea of course. Do not try (b) – shallow water and coastline is exactly what you want to get away from. In fact, you should move towards the deepest spot in the ocean you can reach before the waves hit you, no matter whether that means going towards the epicenter, away from it, or laterally to the wave’s movement.
Btw, I am not an oceanographer or a sailor, this is just what I picked up from reading about tsunamis over the pas couple of days. So if you plan to find yourself in this situation anytime soon, you might want to get a second opinion.
Yep, open water is the place to be. As an aside, Ellen MacArthur was out in the Indian Ocean on her round-the-world sailing attempt when the tsunami hit, and was unaffected…
My understanding is that it isn’t the water that is moving, but the wave. If you’re dog-paddling where a wave comes by, you bob up and down rather than move forward. Am I misinformed?
I’m curious about things in the path of the wave in deep ocean. Is it a wall of water moving at 500 mph, or a shock wave? What happens to fish, scuba divers, submarines, etc. under water?
Not sure about in the deep ocean, but the Independent yesterday had a bit about some scuba divers who were off the coast of Thailand here at the bottom of the page.
As I’m wont to do one day a year or so ago I was watching History/Discovery channel (not sure which) and it talked about a South American man who surfed an incoming tidal wave to save his own life, and apparently it worked.
Also, it is the surge that is travelling 500 mph, the “tidal wave” itself never reaches such a speed, as the entire thing is slowed down considerably as it gets closer to shore.
Also, in “The Perfect Storm” the fishing boat involved is deep in the North Atlantic and are caught by one of the nasty storms there that have claimed many lives over the centuries, they were not the victims of a Tsunami or seismologic event of any kind.
Since a really big tsunami has a height in deep water on the order of 20-30m above and below normal, it probably doesn’t represent much of a threat to a sub (though the change in pressure would certainly be noticeable).
Water is not moving at 500 mph across the ocean. It is an energy wave that is moving at 500 mph. As mentioned this is why objects bob up and down in waves and are (generally) not pushed forward with them. If the tsunami actually had to push water at 500 mph it would sputter out pretty quickly. As powerful as it is shoving the mass of sea water we are talking about here at those speeds would sap the wave of energy very quickly and it would not go far.
When the wave reaches shore the wave will start to hit the bottom and gets pushed up (and slowed down as well). This carries water up and we see the wave rise out of the ocean.
So, the scuba divers mentioned earlier were probably in shallow enough water for the wave to strike bottom and start kicking things (including them) up. If you were treading water in the open ocean you probably wouldn’t even know it passed. The size of the tsunami will determine how shallow the water needs to be before it appears on the surface. In another thread a megatsunami (one far bigger than just happened and actually possible albeit thankfully ultra-rare) you would need to get past the continental shelf to find water deep enough to avoid it effects.
Well, it’s not exactly a shock wave. Shock waves are characterized by sharp discontinuities in a flow, and are extremely thin, like a sheet of paper. The fluid on one side of the vae can have very different velocity, temperature, and density from the other side, only a fraction of an inch away. this is not usually how fluids behave, that’s why shock waves are so interesting.
Nor is it a moving wall of water. If you were to label and follow a particular chunk of water as the tsunami goes by, you would find that it satys more or less in place. It will move in a circle whose size is determined by the amplitude and wavelength of the wave. But in the end, none of the water really goes anywhere. When it breaks on land, things get more complicated. But the very nature of waves in a medium is that the energy moves along without transferring mass. Think of making waves by snapping a rope. the waves move along the rope, but the mass of the rope remains in the same place.
What the tsunami really is is analagous to that rope. It’s a localized displacement, a disturbance, that moves through the water. Notice I said the disturbance moves, but not the water itself.
Possible. Tsunamis don’t need to be 100 feet high. Unlikely though as they are quite turbulant and do not create neat “tubes” like Hawaii’s North Shore (where professional surfers actually do surf 40 foot ‘wind waves’).
Your best option is to head straight out to sea as fast as you can. A tsunami is indetectable on the open sea. At the very least, you want your boat to be far enough out that even if the tsunami breaks on you it won’t hurl your boat against anything.
No. Even though surface or ‘wind waves’ (as in created by the wind) can be much higher than a tsunami (ie the 100 foot Andrea Gaile swamping wave) they have much less energy because (I’m trying to recall from coastal engineering class a few years back) they essentially are only on the surface and consist of less mass. That’s why they tend to sputter out relatively quickly once their energy source (a storm) subsides. This is not to be confused with a ‘storm surge’ from a hurricane where atmospheric pressure creates a ‘bubble’ of water.
A tsunami really involves the whole depth of the ocean so it is packing a whole lot of energy when it hits. Think of it like getting hit by a truck vs getting hit by a slow relentlessly moving train.
One thing to notice in the videos is that it did not hit like a giant wall of water like Deep Impact or the Abyss Directors Cut. Most people did not seem to realize the danger until the wave broke…and then just kept on coming.
When in a boat, the general rule of thumb is to head into the wave, or have your stern to the wave. Do not get sideways - that’s the worst thing to do. If you remember in the movie the Perfect Storm, all the ships and boats (with the exception of the Coast Guard cutter during the rescue) were trying to steer into the weather and waves so they would not capsize.
I seem to recall (although it has admittedly been 20+ years since I was taught this in class) to drive a boat bow first up a wave and then sideslip (boat parallel to wave) down the backside of the wave. Rinse and repeat as necessary. I cannot recall being given a reason for that but I assumed it was so the boat did not nose into the trough of the waves and have the next wave come over the top of your bow and drive you under.
A coworker was relating to me yesterday how a week or two ago while he was vacationing on a large cruise ship in the Caribbean their vessel was apparently hit by something, causing a large shudder to be felt by everyone aboard. The captain shut down the engines for 3 1/2 hours and completely check the ship over but could find nothing. As it turns out the were right over the epicenter of an earthquake and apparently felt the seismic pulse as it moved upward.
That is the procedure a friend and I followed when we were caught out in the open water during a gale. We were in an 18 ft Boston Whaler. We gunned the boat up the face of the oncoming wave then, once on the backside, turned the boat parallel to the wave and shot along the backside to gain a few yards towards shore before turning back into the next wave. It is a long and exhausting experience, but keeps one safe, relatively speaking.
Ignoring all of the tsunami speculation (interesting though it may be) I would point out that rum/sex has never failed to be a good choice when I have made it.
Yeah, pretty much. I’ll tell you what they teach Coast Guard coxswains. Bear in mind that driving different boats in different seas has pretty much become more detailed science than art, so this is very basic.
For normal boat operations in heavy weather, you’re taught to drive bow into the oncoming wave, at an angle of 10-25 degrees. Provided the wave remains somewhat constant in your expectations, you would drive over it this way, then straighten out as necessary. This is to keep as much of the boat, its rudders and screws waterborne, maximizing control. Plus it helps in keeping the bow from knifing under on the backside.
If the wave begins to break, you have some options. If time and distance permit, back down square to the wave (keeping bow to), and allow the break to occur, so that by the time it reaches you, it’s mostly aerated foam and water. The big thing is, avoid letting it break on the boat. Obviously. If you find yourself too close to a break, you’d actually want to throttle up a bit - this will raise the bow a bit and help to keep it above water. If you lose your bow into the face of a breaking wave, that’s bad[sup]TM[/sup].