Despite the common vernacular calling them "waves" they're really more like really really high tides. You're talking about something that happens over, say, 10-90 minutes, not seconds.
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.
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.
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.
I am just having a bit of linguistic fun. Tsunami is a great clear distinct term for what can be a very destructive event.
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.
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.
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)
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.
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.
(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)
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.
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.