Energy waves - Tsunami

askold · Dec 29, 2004

My understanding is that a Tsunami is just another energy wave - just like the kind that occur in astronomy when a comet strikes Jupiter. What would happen to a submerged submarine when the Tsunami energy wave passes through it. It would seem to cause quite a jolt to the sub. I wonder if the US fleet takes any action to avoid the Tsunami?

newtonian · Dec 29, 2004

My understanding is that in the open ocean the tsunami is not very destructive, albeit travelling some 500 mph! The rise is sea level is gradual and surface ships should be fine. In shallow water, however, the wave slows down, to as slow as 30 mph, and the energy goes into height of water and the destruction is - well, its on the news! However, I wonder if any subs were near the earthquake underwater zone? Anyone know? Near the fault the entire ocean of whatever depth (?) would clearly be disturbed.

newtonian · Dec 29, 2004

Askold- Here is an article excerpt you may find interesting on tsunamis: "Killer Waves-Myths and Realities THE sun had set just a few minutes earlier. On this tranquil Friday, July 17, 1998, the men, women, and children of several small villages on the northern coast of Papua New Guinea were suddenly shaken by a magnitude-7.1 earthquake. "The main shock," says Scientific American, "rocked 30 kilometers (nearly 19 miles) of coastline . . . and suddenly deformed the offshore ocean bottom. The normally flat sea surface lurched upward in response, giving birth to a fearsome tsunami." An observer says that he heard what sounded like distant thunder, which gradually faded as the sea slowly receded below the normal low-water mark. A few minutes later, he spotted the first wave, which was about ten feet [3 m] high. It overtook him as he was trying to run away from it. A second, larger wave flattened his village and swept him along for nearly a mile [1 km], into a nearby mangrove forest. "Debris hanging from the tops of palm trees indicated that the waves reached heights of 14 meters [46 feet]," reports Science News. That evening giant waves took the lives of at least 2,500 people. As a twist of irony, a lumber company later donated timber for new schools, but there were virtually no children left to go to school. Almost all-more than 230-had been killed by the tsunami. What Are Tsunamis? Tsunami is a Japanese word that means "harbor wave." This is "a fitting term," says the book Tsunami!, "as these giant waves have frequently brought death and destruction to Japanese harbors and coastal villages." What gives these freak waves their awesome power and size? Tsunamis are sometimes called tidal waves. Strictly speaking, however, tidal waves are simply the surging and waning swells that we call tides and are caused by the gravitational pull of the sun and the moon. Even the massive waves-sometimes over 90 feet [25 m]

Saiph · Dec 29, 2004

Submarines and boats in the open ocean don't really notice them at all. They are still immensly powerful waves, however since they go so deep (i.e. are so large) all their energy is spread out. As such the impact of the wave passing you is minimal in the open ocean. On the coast however, the rising sea floor pushes the wave base (i.e. the bottom) up to towards the surface, helping to concentrate the energy. The wave also slows down, so the following wavecrests pile onto the first, slower sections, causing the entire wave to compact and become concentrated (just like a multi-car crash). Add into that various coastal features that can focus the wave (just like lenses do with light), like harbors, or underwater valleys, and it can be magnified even further. So you take a strong, but spread out wave in the ocean, and compress it into one big punch. Then throw it against an unsuspecting coastal populace....and you get disaster. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

newtonian · Dec 29, 2004

Saiph- Hi! Well said, more concisely than I. However, this particular event involved, according to TV reports, movement of a fault on a 600 mile section of some 100 feet rather suddenly. I would think that would be somewhat violent near the actual underwater earthquake zone. So I am curious if there were any subs near the actual earthquake fault area.

askold · Dec 29, 2004

I understand that when the tsunami gets into shallow water its character changes to that of a normal wave - just real big. In the open ocean, I thought that the tsunami was more like a compresion wave - almost like a sound wave travelling through the water only with a very large displacement (amplitude). The displacement being the amount that the ocean floor inititially moved. It would seem that a sub would notice a 700mph, 100ft amplitude waving going past.

newtonian · Dec 29, 2004

askold - No, it is not normal at the coast - as per my previous posts. The wave in mid ocean has a gradual rise of about 10 feet, again I quote the same article: "Yet, despite their speed, they are not dangerous in deep water. Why? First, because on the open sea, a single wave is usually less than ten feet [3 m] high; and second, because the wave can be hundreds of miles from crest to crest, giving it a gentle slope. Hence, tsunamis can pass under ships without even being noticed. The master of a ship lying off the coast of one of the Hawaiian Islands was not even aware that a tsunami had passed by until he saw huge waves pounding the distant shore. " - Ibid., pp. 25,26 I'll bow to someone else on the amplitude thing.

Saiph · Dec 29, 2004

nope, that sounds good to me. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

askold · Dec 30, 2004

OK, I'll buy that - thanks for the info. I'm a little out of my depth with this subject (pun intended).

claywoman · Dec 30, 2004

I am fascinated by all I learn on this site!!! Thanks everyone!!!

siarad · Jan 2, 2005

Interesting question. I'm assuming the underwater waves would act as surface waves & simply move the sub. in a circle leaving it as it started. At 500mph this would seemingly be very violent but incredibly short lived. I've no idea how large the circle would be & may be so small as to be unnoticeable. I guess the most likely place to find out is where tsunami detectors are described. Strictly speaking the coastal damage is caused by breakers not waves similarly with ships.

Saiph · Jan 2, 2005

it's travelling by at 500 mph, but the waves are so long it takes ~10 minutes for a crest to go by. A boat, and a sub, wouldn't really notice it at all. Would you notice a 10ft change in elevation over ten minutes? <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

claywoman · Jan 4, 2005

I don't know about submarines, but I do recall one story that stuck with me about a newlywed couple scuba diving off Sumatra. they apparently were far enough away from the earthquake and were diving near some corral. The were underwater during the tsunami and felt something that swirled them enough they lost their bearings and couldn't tell up from down. When one of them got their bearings finally and discovered up, they both surfaced after coming up slowly to prevent the bends. Their boat was floating just about where they left it. Eventually they headed for land and the closer to land they came, the more dead bodies they saw floating on the water. When they got back to where their hotel had been they saw the damage from the tsunami. So I don't know about ships, but if divers didn't really get much tumbling around, some but they continued to dive in another spot before heading back, it mustn't have been that bad...

Saiph · Jan 5, 2005

sounds about right, they were also pretty close to shore (compared to subs anyway), which amplifies the effects. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

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