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Comment by ggm | Hacker News Reader

Bear in mind that a mass of water moving with enough energy to form a cohesive whole won't always present as a breaking wave. It's when it collides with something it builds up into a breaker. That something can be another mass of water. Typically it's rising land to the beach or cliff. Or a contained body of water. Some of the truly huge tsunami waves were compressed by the landscape.

If you look at videos of the fukashima tsunami it's not "great wave off Kanagawa" as much as an unavoidable rising mass of water, inexorably pushing all and everything it confronts ahead of it, or subsuming it into the body.

(Not a hydrologist)

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Depends on the surrounding terrain and if you are on street level. This video here has moments that if you are on street level it crashes all around 4:30 https://youtu.be/EPjliKVtmUA?si=5ELV7bnxkQBa_xZt

For example last year's Greenland Tsunami that was in a fjord reached 200m height and a top speed of 150km per hour.

Wow, I was really sad to see the number of people still running/driving up that narrow street as the waves crashed in, absolutely tragic.

> For example last year's Greenland Tsunami that was in a fjord reached 200m height and a top speed of 150km per hour.

There is no video right?

No video since nobody was around, just one abandoned station. But - the waves revertebrated in the fjords for next 9 days as its seismic impact was recorded all over the world.

Yeah, I read that, that's why I wanted to see if there was a video :(

Landslip / glacierslip 'tsunamis' in confined waters are not really the same as those from subsea earthquakes. The landslips just slop the water along the fjord or bay. The volume of water is tiny compared to big 9.0 oceanic quakes, like those for the Indian Ocean (2004) or Japanese (2011) tsunamis. We really need a different word for the local landslip type.

Here is a famous landslip-tsunami event with one eyewitness account:

https://en.wikipedia.org/wiki/1958_Lituya_Bay_earthquake_and...

See the book Wildest Alaska: Journeys of Great Peril in Lituya Bay by Philip Fradkin.

P.S. Yes, an earthquake triggered the landslip, but the earthquake did not displace the water.

There wasn't a breaking wave in the Japan tsunami:

https://en.wikipedia.org/wiki/Breaking_wave

In the video you are seeing the incoming flow of water smash into structures and splash into the air.

Your video supports the comment you are replying to. What you are seeing is water splashing up as it rolls into the buildings.

Compare to this image from the Wikipedia article about the Lituya Bay megatsunami: https://upload.wikimedia.org/wikipedia/commons/thumb/0/0b/Li...

Yes, Fukushima looked a lot like a flash flood compared to the kind of wave portrayed in apocalypse themed movies.

> water moving

The complexity comes from the fact that water moves mostly up-down in a wave, not horizontally. It's _wave_ front that moves horizontally towards a beach.

Missing the point a little, tsunami's are not comparable to ocean waves. They ARE more like a huge, very fast, rising tide, modelling is not the same as a breaking ocean wave. This research impacts the modelling for ocean or coastal structures which have relied on the breaking wave dynamics for a particular depth and topology. The research shows that the maximum breaking wave height can be much greater than previously thought. So, the off-shore wind turbine which was believed safe because the expected max wave height will never manifest as a breaking wave in the depth of water it's sitting in may actually be in jeopardy.

Or, and that's the most important one you missed, "just air". If there's enough air movement to offer an opposing force, that wave gets broken.

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