[dgfitz]

> I'm surprised so many people don't understand what tsunamis are.

“I’m Surprised so many people don’t know what ‘X’ is/are isn’t a very nice thing to say. Your comment could have done without that, the rest of it would have been fine.

[hsbauauvhabzb]

I don’t take offence. I’m not the most educated, and I don’t live in or near a tsunami prone area, I know about other natural disasters that are relevant to where I live though, maybe more than the parent poster.

[ninetyninenine]

I don't think he's even right. Like what he is saying is in actuality wrong. He's surprised because he's ignorant. I'm all for people saying stuff the way he says it. He believes it's true, then he should stand behind. But then the consequence is that he needs to be accepting of when people call him out for being utterly wrong.

[K0balt]

The difference is that people know what 2m (wind driven) waves look like at their cities seawall. A 2m tsunami is a -completely- different phenomenon, because of its length. Depending upon the underwater geography, a 2m tsunami might flood right over their 3m seawall, and wipe out entire parts of the city, sweeping hundreds of people out to sea. A 2m wind wave will get saltwater spray on cars driving by. They are both waves, but they share very little in characteristics other than their fundamental physics. It’s like saying that a slingshot fires a 12mm projectile, and so does a 50 caliber anti material rifle. The fact that they are both projectiles, of the same size, is much, much less informative than other facts about their nature.

Saying that tsunamis are waves is easy to equivocate into tsunamis are waves, like other waves. This is an equivocation that is very misleading and can get people killed.

Insofar as the goal of communication is to communicate meaningful information, it is less accurate to say “tsunamis are waves” than it is to say “tsunamis are nothing like normal waves”, or to say “tsunamis are like a wall of water, not like a wave” or “tsunamis are more like tides than waves”.

So yes, tsunamis are waves, but insisting that tsunamis are waves without qualification that their effective characteristics are fundamentally much different and more dangerous than a regular wave is misleading through omission in a way that could directly put people’s lives in jeopardy.

Being pedantic about definitions and being accurate in conveying meaning are not the same thing, and communicating in good faith normally is about conveying meaning in an accurate manner, not just using words in an accurate manner.

FWIW I also believe that meanings are important, but there is a point where pedantry falls into bad-faith territory.

[fc417fc802]

I appreciate your effort to provide an understandable explanation.

That said, in context the original statement was so extremely misrepresentative of the reality that I felt it left the realm of "inaccurate but effective for communication". I certainly didn't see the objections as pedantic.

[K0balt]

A clarification was appropriate because it really did miss the physics, but doubling down on the definition of wave without talking about speed, length, and volume (which is what had confused OP in the first place) was not only suboptimal in teaching useful knowledge to OP, it was also misleading in a way that could (and did, in at least one case of a commenter in this thread) lead to a dangerous misconception about characterising tsunamis.

Perhaps it wasn’t intentionally pedantic, but the way that it was doubled down on later makes me suspect an argument in bad faith, or at least an epic case of missing the opportunity to usefully inform.

I value this site for the general character of people trying to educate more than just troll, and I think it’s important to try to educate trolls as well to understand a more constructive and respectful way to interact here. Ostensibly, we take off our clown shoes and leave them at the door.

OTOH I may have read multiple comments in similar tone that were not all attributed to one poster , giving me a mistaken impression of the intent. In that case, I owe an apology for perhaps overreacting.

[throwup238]

Nitpick: while what you say is generally true, there are several scenarios that can create true dramatic “wall of water” tsunami waves that have leading slopes of 45-90 degrees and heights in the tens of meters.

The most obvious (but relatively rare) are tsunamis amplified by submarine canyons and other coastal bathymetry like the Nazare submarine canyon famous for the biggest waves on the planet (50+ footers are common in season). If an earthquake directs a tsunami at that canyon, the resulting waves will be spectacular and probably drown everything north of the cliffs. Unfortunately we don’t have any historical records about what happened at Nazare after the 1755 Lisbon earthquake so we don’t know just how big those waves can get.

Then there’s landslides like the one that caused the 1958 tsunami in Lituya Bay, Alaska which creates a much more sudden displacement than an earthquake. Based on the surrounding mountainsides the wave created from that landslide might have peaked at ~500 meters without the 100+ mile wavelength you’d see in a normal tsunami wave.

The most common however are tidal bores, which can send a 30+ foot vertical wave down rivers and narrow channels. This phenomenon shows up relatively frequently in earthquake youtube videos near rivers, though the wall is usually only 5-10 ft tall.

[K0balt]

Oh yes! It’s absolutely true that underwater geography can steepen the wave front and amplify the height, sometimes by orders of magnitude. The deep water height of a tsunami wave is often a lot different from what you will see at the coastline.

An entertaining anecdote from the pre- smartphone era:

I sailed to the site near Chenega bay where the earthquake wiped out the village in 1958. We got permission from the elders at the Chenega bay village to land at the island, and it was extremely humbling to see the high water mark from the coastline, and to see the wreckage of boats far, far up on mountainsides.

I’m not a big believer in supernatural stuff, and there are plenty of alternative explanations, but it still freaks me out a bit that the photos we took (aside from the digital ones) did not develop any images of the village site. It was white as if it had been overexposed, even in the case of 1/2 frames. On both disposable cameras. Other photos from the same day, taken in other directions, turned out fine. The digital camera fell overboard in 500 fathoms, so we lost those photos the next day.

As for how exactly this could happen in any reasonable version of events, I’ve got nothing. I guess sometimes chance events line up just right to make for a good story.

Interestingly, there are big tidal bores frequently in Turnagain arm, with 1-3m being common. I’ve seen people surfing it with wetsuits in the ice cold water, getting a run of several miles lol.

[throwup238]

> Interestingly, there are big tidal bores frequently in Turnagain arm, with 1-3m being common. I’ve seen people surfing it with wetsuits in the ice cold water, getting a run of several miles lol.

That’s going on the bucket list! How dangerous is it? If you biff it and get caught by the wave can you just dive under the wavefront and come up behind it like on a beach?

[K0balt]

I don’t know much about the dangers involved, but it isn’t (or wasn’t, AFAIK) a big attraction… so maybe it’s crazy or dangerous? I’m not sure. Or it might be because the water is so cold that hypothermia and death is inevitable in less than an hour? Or because there probably is no realistic chance of rescue if something goes wrong?

At any rate, there was enough people willing to try that I saw it a couple of times, and TBF I think windsurfing isn’t too unusual in the arm now. But there is also trees and stuff in the tidal bores sometimes, so maybe debris is a big problem or the area is too shallow to be safe.

But, if it’s doable, I’m sure it would be memorable!

[ninetyninenine]

I think you’re out of touch. A tsunami is a wave both from a pedantic perspective and an intuitive one and most people aren’t deceived into thinking that tsunamis aren’t dangerous at all because it’s a wave. That’s just made up garbage.

You’re like coming up to me and saying hurricane is not wind because it’s dangerous to think of a hurricane as only wind.

Dude. Nobody is thinking hurricanes are just chill just because hurricanes are wind. This is a fucking non-issue.

I think what you’re trying to say is that the wave length of a tsunami is much longer than the amplitude even though the amplitude is still epically high. But don’t try to conflate this with a safety issue of people dying because somebody called it a “wave” that’s just garbage.

[K0balt]

So, I’m sorry that I evidently didn’t manage to convey my point effectively. The problem is that wave is accompanied by a measurement that deceptively buries the lede.

Everyone knows hurricanes are wind. So they look for the wind speed to understand the threat. And it’s effective at characterizing the threat. A 100mph wind is going to be similarly destructive as any other 100mph wind. It works and is semantically and linguistically accurate.

Everyone knows a tsunami is a wave, and it is a strong intuition to believe that a wave is defined by its height. , and the height of the tsunami is actually one of the most widely reported metrics. But intuition about the effects of a tsunami by wave height is dangerously wrong. A tsunami is not at all similar to the vast, vast majority of waves in character and effect. Its speed and length at way, way out of band, and are seldom reported.

[lief79]

My understanding is the most deadly/destructive parts of hurricanes are usually:

1. the storm surge, the potential wall of water brought by the continuous winds and waves near the shore, followed by 2. the flooding from heavy rains, then 3. followed by the wind.

So your example might also be hitting the same issue you're trying to avoid.

Note, the worst storm surge is from the eye towards the side where the winds are blowing in the direction of the shore. That's only part of the area with the peak winds.

[K0balt]

Good points. Where I am at it’s mostly the wind because I am a well drained higher elevation, so I’m sure that coloured my perception. But you are right, the storm surge and flooding also do a great deal of damage.

[RugnirViking]

Idk. I don't live anywhere where tsunamis are an issue but seeing measurements like a 1m wave does make me wonder about waves I see at the beach that are that high regularly. I find myself going "oh not so bad then" only to read about thousands of people being evacuated and major damage

[nathos]

Obligatory https://xkcd.com/1053/