Someone threw a brick into the ocean off a cliff somewhere?
Undersea volcanic explosion near Tonga
More like a large block of tuff....
https://www.youtube.com/watch?v=B54HbfqDbK4
My impression is that there was a landslide and lateral blast under water from this volcano. See Mt St Helens for what that looks like above sea level.
Will be interesting to see what the final verdict is about what happened at Hunga Tonga-Hunga Ha’apai. Might be weeks to months for that though, I suspect that there are few to no local volcanologists and access to that area is considered very hazardous to your health.