To completely disregard anything both the prequels and the sequels have to say on the subject, how would you classify Darth Vader's scars as per what can be observed in The Empire Strikes Back? They look like blade slash wounds, or shrapnel scars, or perhaps weird keloids, but I'm not sure about anything.

I know George Lucas always wanted a volcano involved, but makeup artists can't exactly find guys who fell in volcanoes, for a very obvious reason, so they have to reference something else entirely. What do you think was referenced here?