Yeah the title probably doesn't make a whole lot of sense but I'll include an image which hopefully explains it a little better.

When you explode a nuke underwater this is the pattern that it leaves behind and I can't imagine that that's intended.

I have this setting set at this btw:

''#The scale of nuclear bomb destruction. multiply this by 16 to get the radius of a nuclear bomb explosion.
#Range: 0.0 ~ 1.7976931348623157E308
nuclear_explosion_size_modifier = 3.67''

Idk if it's of any relevance but maybe it has something to do with the weird terrain destruction.

I get a simlar result but instead outlines of water chunks are left behind instead of the bomb just destroying and leaving water chunks, this is with the default nuclear explosion setting, their also arent aligned to regular minecraft F3+G chunks

It's the same for me in lava (v1.0.4)

Here's another example of weird water/lava destruction from a nuke