I read about how tsunamis cause massively high, towering waves, but the YouTube footage of tsunamis - such as the March 2011 Tohoku quake - shows merely a lot of seawater relatively gently flooding over the Japanese coast as it arrives at shore.
Did the 100-foot high waves dissipate at sea before hitting land?
There is a misconception that tsunamis are giant waves that can be spotted far out at sea. They aren’t. In fact, ocean going ships and submarines won’t even notice them as they pass. Instead, they are a giant wall of energy that only becomes apparent when they reach land. The English term “tidal wave” is more descriptive because they are like a huge tidal surge rather than a rogue wave. However, there is nothing gentle about a large one. The entire ocean recedes and then rises much higher than normal to swallow up everything close to sea level.
- YouTube (skip to about the 6 minute mark for the devastation).
Tsunamis make really big waves, but they aren’t big breaking waves like some people picture. They are very long period waves, so they look more like a really big tide that keeps coming in. That’s why they are sometimes called tidal waves, though scientists don’t like that term since there’s nothing tidal about their formation. Instead of being over in a few seconds like a typical breaking wave, the period of a tsunami can be several minutes to more than an hour.
They can also easily be a lot more than 100 feet. The record height for a tsunami is 1720 feet. See here for details:
Right. Out at sea, tsunamis are typically only a few feet high, but can be 100 miles in length, very different from a normal surface wave. At sea they travel at high speeds; 500 miles per hour is not atypical, but even at that speed, it can take a long time, 15-30 minutes, for the water to rise and fall as the wave passes by, even though it only rises a few feet. The wave is therefore barely noticeable at sea. When it approaches shore, the shallower waters near land force the wave to slow down, the leading edge slowing first since it reaches the shallower water first. This causes the water to start “piling up”, since the trailing part of the wave is traveling faster than the leading part. This reduces the wavelength and greatly increases the height. Thus the Japanese name “tsunami”, which means “harbor wave”, since the wave is only noticeable when it approaches land.
I suspect people sometimes confuse tsunamis with rogue waves, which have been recorded pretty close to 100 ft.
Most people I think have at least seen the famous Japanese print, The Great Wave off Kanagawa by the artist Katsushika Hokusai, often mistakenly thought to be of a tsunami, but really a rogue wave.
Have a look at this
OK, thanks for the replies…so the “height” is not what we usually think of as “height?” It’s like amplitude, added up? So a tsunami can appear to be only 2-3 feet tall, but if it’s a very long wave, it adds up at all of its segments and becomes officially recorded as a 100 foot high wave?
Do you have a cite for a tsunami being recorded as 100 feet high? I don’t think I have even seen this.
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Yeah, it’s difficult for us to judge how “something you’ve read” is wrong or possibly correct. Just like with tides geography will make a big difference to how high a tsunami will be when it inundates the shore, and unlike the tide the energy of a tsunami varies a whole lot. Send a high volume tsunami in a narrowing inlet and it definitely could reach a 100 feet.
According to this article, the largest known tsunami occurred in 1958 in Lituya Bay, Alaska - a narrow inlet.
“The force of the wave removed all trees and vegetation from elevations as high as 1720 feet (524 meters) above sea level.”
There are some videos, photos and personal accounts on the page.
I believe the total height is how deep the water gets on shore. But it takes a while to get that deep-it doesn’t crash down.
If megatsunamis count - the variety created by things like major impacts and landmass collapses - then they can get as high as three milestall.
No. I highly doubt that. But we’ll be able to clear that up once you give some examples of 100-foot tsunamis you’ve read about.
No. Re-read markn+'s post above. The tsunami out at sea may be fairly small, but as it gets close to shore the height increases dramatically.
For example, the 2009 Samoa earthquake’s tsunami measured 3 inches at the epicenter, in the ocean. At its highest point on the Samoan coast, it reached 46 feet.
The 2004 Indian Ocean earthquake’s tsunami measured approximately 33 meters (108 feet). Wikipedia doesn’t say exactly where that was measured.
2011 Tōhoku earthquake and tsunami (the one that led to all of the problems with the Fukushima Nuclear Power Plant) measured 133 feet at Miyako, in the Japanese prefecture of Iwate.
Video of the event: https://www.youtube.com/watch?v=VqIQFZZoVR4
This article says otherwise, it says the Alaska Tsunami was 100 feet high and that it caused damage at 1700 feet upslope. Thats not the same thing as saying a tsunami is 1700 feet high.
What Are the Biggest Waves in Recorded History? | Science| Smithsonian Magazine and Scientist Confirm the Largest Wave Ever Recorded