"How deep do caustics go?"

Errm.. this is more a complex physics light problem than anything else.
It involves various variables, including (assuming in water):

• The surface of the water (how turbulent it is, which alters the angle of incidence as the light hits the surface).

• The density of the water (which alters both the amount of light absorbed as it travels through the water and the light's refraction) - salt water has a different density compared with fresh water (which is why it's easy to float in the Dead Sea - high density there).

• The clarity of the water (more silt, less light).

And probably a lot more stuff that I don't know about.

As for what a depth-charge looks like when exploding, I have no idea. But I'd hazard a (total) guess...

There'd be bubbles (expanding radially outwards from the source of the explosion), caused by heat of the explosion turning the surrounding water to steam (a gas, hence bubbles - just look into a boiling kettle to see what I mean). There'd also be radical changes to the local water densities (so radical changes to the caustics). And, of course, there'd be the usual effects of an explosion (very similar to an explosion in the air), of bits of the depth-charge flying (swimming??) away from the source.... (but more slowly, 'cos of the drag of the water, as compared to air)...

Oh, and of course, at the time of the explosion (and briefly thereafter), some bright areas (not flames, but centres of intense heat)...

Probably not much help, but the best I could do on this very clammy night in the UK...

Cheers,
Diolma