TL;DR
When you set off a nuke (or explosive rocket?) there should be a crater left over after the explosion.What ?
With the introduction of cliffs there can be craters in the landscape: My suggestion is to create such craters when setting off any large explosive, In vanilla this would probably be just nukes. But mods like the orbital canon would qualify too. Explosive rockets might qualify but probably don't have a large enough explosive radius for a crater.A crater that overlaps water should probably filled with water instead but one could also argue that the explosion creates a wall around the crater preventing water to flow in. Either way works.