[s_m_t]

It can be a very long wave. If you have a coastal area that is mostly at or very close to sea level then that entire area could now be 3m underwater which is very bad.

Also, even under normal conditions the type of wave you would see at the beach with a height of 3m is insanely powerful. I think the highest I have body surfed in was maybe 2-2.5m and if you get caught in the break of the wave you are literally powerless and get dragged under water and spun around for quite some distance. It is a bizarre experience and doesn't really match the basic intuition of how powerful it should be.

[lloeki]

My crude understanding and associated mental imagery is that tsunami waves are more like tide than "usual" waves: your typical 3m wave is mostly "surface-ish" in comparison, while 3m tsunami has both greater wavelength and "depth", which is what makes the "usual" wave break quickly when it reaches shore, whereas tsunami waves continue pushing real hard for real long because of all the length * undersurface water you don't see.

Gently shaking a glass of water sideways or blowing upon it won't make much water spill out, but jolt it vertically and most of it goes out real quick.

This is all probably very incorrect physics but it helps drive my intuitive understanding that 3m wave and 3m tsunami are quite different, the former being scary but the latter being muuuuch scarier.

[yosito]

Yep, where I live (rent) a 3m wave would fill my house with 1m of water. Even if it was one quick wave, that washed over without staying long enough to completely flood the inside of my house, I'd probably at least have to deal with a bunch of water damage.

[Someone]

I would be more worried about the force of the water hitting things and about objects it drags with it than about water damage.

One meter of water weighs 1000kg/m². If a wave a few meters long slams into a wall of your house, that can easily be more force than that of a decent sized car doing the same.

[defrost]

Our local offshore break that we grew up with as kids was, and still is, a total monster in storm (a long way back and out to sea) conditions:

https://www.youtube.com/watch?v=xjHaFOGBPzk&t=138s

https://www.surfertoday.com/surfing/the-right-the-monster-we...

It's a little bigger than 3m at the face and is a "slab" .. not a thin wave but one backed by a mass of water.

Somewhere in that video you might see a triple lip .. three curling breaks, one within another and another again.

[lukan]

I know 3 m waves are powerful, I was within them.

But they are normal on most coast and that they are bad on a flat beach I can imagine. But Taiwan is quite steep, so aside from some damaged boathouses, I cannot see the big danger (compared to the consequences of the earth quake). But apparently no Tsunami came.