This is also in many ways what makes them so deadly in places that aren't used to tsunamis. It often just looks like a regular wave or a tide that will imminently break or recede, but they never do. Here [1] is a video of one of the later waves of Thailand's 2004 tsunami.

Even worse is tsunamis are also often preceded by a 'disappearing coast' effect where the water will recede back into the ocean for hundreds of meters. This often drives tourists or locals who don't know better to go check out the sea bed and the weird behavior of the ocean, then the tsunami comes in and they're right in the middle of it.

If you're ever at a beach where the water starts rapidly disappearing, yell tsunami and get away as fast as you can. Ignore the normalcy bias, because most people, even locals, will be just standing around taking videos or even walking out into it. And don't stop running even when you're well away from the beach. It's nature's warning sign.

[1] - https://www.youtube.com/watch?v=WO7TZFBAlaE

>Here [1] is a video of one of the later waves of Thailand's 2004 tsunami

If that is the one of December 2004, it affected not just Thailand, but also many other countries around the Indian Ocean:

https://en.m.wikipedia.org/wiki/2004_Indian_Ocean_earthquake...

Excerpts:

2004 Indian Ocean earthquake and tsunami

On 26 December 2004, at 07:58:53 local time (UTC+7), a major earthquake with a magnitude of 9.2–9.3 Mw struck with an epicentre off the west coast of Aceh in northern Sumatra, Indonesia. The undersea megathrust earthquake, known in the scientific community as the Sumatra–Andaman earthquake,[8][9] was caused by a rupture along the fault between the Burma plate and the Indian plate, and reached a Mercalli intensity of IX in some areas.

A massive tsunami with waves up to 30 m (100 ft) high, known as the Boxing Day Tsunami after the Boxing Day holiday, or as the Asian Tsunami,[10] devastated communities along the surrounding coasts of the Indian Ocean, killing an estimated 227,898 people in 14 countries, violently in Aceh (Indonesia), and severely in Sri Lanka, Tamil Nadu (India), and Khao Lak (Thailand). The direct result was major disruption to living conditions and commerce in coastal provinces of surrounding countries. It is the deadliest natural disaster of the 21st century,[11] one of the deadliest natural disasters in recorded history, and the worst tsunami disaster in history.[12] It is also the worst natural disaster in the history of Indonesia, Maldives, Sri Lanka and Thailand.[13]

It is the most powerful earthquake ever recorded in Asia, the most powerful earthquake in the 21st century, and the third or second most powerful earthquake ever recorded in the world since modern seismography began in 1900.[14][a] It had the longest fault rupture ever observed, between 1,200 km and 1,300 km (720 mi and 780 mi), and had the longest duration of faulting ever observed, at least ten minutes.[18] It caused the planet to vibrate as much as 10 mm (0.4 in),[19] and also remotely triggered earthquakes as far away as Alaska.[20] Its epicentre was between Simeulue and mainland Sumatra.[21] The plight of the affected people and countries prompted a worldwide humanitarian response, with donations totalling more than US$14 billion[22] (equivalent to US$23 billion in 2024 currency).

I was around (in India) at the time, but not near the coast, much further inland and to the north, so was not affected.

Again the only correct comment is downvoted. Watch Tsunamis on Youtube. The water just keeps coming and coming. They are like high tides.

I remember in 2015 watching this great tsunami video at a harbor. It was about 11 minutes long.

At the start, there's just a white line at the horizon. Then the fishing boats in the harbor start rocking and jangling. Then water starts pouring over some walkways and sea walls.

Eventually the cameraman backs away and starts climbing a concrete tower; water starts to flood over the area where they had been standing. I think they climb a couple stories and are safe up there.

I haven't been able to find the video in years, but I remember being fascinated by it and I'd love to watch it again.

Edit: I never expected to find that video again, but here it is. A little more terrifying than I remember.

https://youtu.be/PvJs2iWQuFs

It never got above the boats, cant be more than a few feet tall

The port's wall slow down the entry of the water and the boats can float. The "tide" caused by the tsunami was several meters.

I feel like you're making a bad joke. Did you drop your /s?

Ah, and here I was wondering if it would be possible to surf one of these for miles in if the timing were right. The grandparent answers that question.

> Again the only correct comment is downvoted.

I seriously wonder if people brains are being cooked these days. One of the blessing of HN used to be it was full of fairly well educated, and most importantly, curious people. Sometimes with a bit too much of a focus of the technical side of things, but at least on most technical topics the comments where a great place to get a richer understanding of a whatever was being discussed.

They are very literally long wavelength waves though.

Yes, they are waves, but they are often very long waves. A typical 1m wave might be 20m long. A tsunami wave might be a kilometer long or longer. That is why people say they are like a tide. The wave arrives, then does not recede for several minutes. So, while a 4m wind driven wave might break over a seawall and even wash a car off the road, a 4m tsunami washes ships over that same seawall and floods the city.

It’s a wave, but it is often not at all like a regular ocean wave. I’ve been at sea when a 3m tsunami passed, we barely felt it. If it had been a 3m wind wave in that otherwise calm sea, it would have knocked dinner off the table.

So are tides.

Perhaps we can just go back to calling them tidal waves. Which is also ambiguous. I guess if I had any point it's just that it's not colloquial to call tsunami waves, its technical. If anything distinguishing based on how they feel compared to regular wind waves is more colloquial.

Honestly tidal wave, a wave that comes in like the tide, might actually be a better term than tsunami (lit Harbor Wave) A wave that destroys your harbor? A wave found in your harbor(a place where there are usually no waves)? What if you are not in a harbor, do you still get a wave?

I am just having a bit of linguistic fun. Tsunami is a great clear distinct term for what can be a very destructive event.

These things are 100% waves. It's not a misnomer. It fits the scientific definition of waves and it fits our intuition of what waves are. These are NOT tides.

https://www.noaa.gov/explainers/science-behind-tsunamis

Yes, they are waves, but they are often very long waves. A typical 1m wave might be 20m long. A tsunami wave might be a kilometer long or longer. That is why people say they are like a tide. The wave arrives, then does not recede for several minutes. So, while a 4m wind driven wave might break over a seawall and even wash a car off the road, a 4m tsunami washes ships over that same seawall and floods the city.

It’s a wave, but it is often not at all like a regular ocean wave. I’ve been at sea when a 3m tsunami passed, we barely felt it. If it had been a 3m wind wave in that otherwise calm sea, it would have knocked dinner off the table.

A tsunami absolutely does not fit our intuition of what waves are. It looks like a wave. But it does not stop. It just continues. That little wave goes on an on, farther and farther inland. After an hour it may still go on. It's a nightmare wave, because it doesn't not fit one's intuition of what waves are.

>It looks like a wave.

and it IS a wave. I don't understand the resistance here. It BOTH is a wave and looks like a wave.

But because it does not stop, it is not a "wave". Let's just stop with the strange pedantism.

I'm reacting against the word "intuition" here. Nobody said it isn't a wave. But it's not like a wave as our intuition says.

(Though it does not _always_ look like a wave - check out the timelapse video from Kuji harbor: https://www.youtube.com/watch?v=M1B1J6sgFxk - that's why you'll sometimes see people talking about it looking like a (very) high tide. As an example of the nightmare "wave" which doesn't stop, and is thus un-intuitive.. https://www.youtube.com/watch?v=3618dZoiaPE which is incidentally also from Kuji, but from 2011)

I know what you’re talking about. But intuitively it’s still a wave.

It's a distinction without value I think. There are waves, and many of them. There is a rise in the sea level. For anywhere affected, both certainly matter. Like you mentioned, tsunami isn't a brief event. And here in Japan, they are talking about tsunami waves, not a singular tsunami. And talking about sea level rise and checking the local power poles for sea level indicators from previous tsunami events and floods.

I is absolutely a VERY valuable distinction because the behavior as it affects humans (up to and including killing them) is VERY different.

Regular waves that are a little higher than your seawall might cause some water damage to the buildings right next to it. A tsunami that is a little higher than your seawall will flood your entire town and drown people who are caught in basements.

Sure, but if you insist it's like a tide you downplay the risk of the initial hit of the wavefronts and the potential for it to slam up the coast or a seawall becoming a larger local wave. And if you insist it's like a wave, you downplay the persistent risk of both follow-up waves and ongoing flooding that won't subside quickly.

So saying it's not waves is dangerous, and saying it's not a sea level rise is dangerous. It's not useful to try and delineate between a tsunami being one of the two when it's in reality an event that consists of both.

(Ignoring that a sea level rise and a long-wavelength wave are the same thing)

They are waves, but they don't behave like the sort of waves we are used to. This is the source of all the confusion.

I have heard description of a tsunami being "a temporary rise in sea level", which describes its behavior much more intuitively. A tsunami that tops a sea wall will flood the entire lower-lying area behind it. A usual wave, even a tall one, will only deposit some splashes of water behind the wall and go away immediately.