perhaps it would be easier to reword the log itself? something to the effect of "Being able to see the size of the explosion, it seems I will be safe as long as I'm not past the dam" This takes it from "I survived it here" to "I witnessed it". you could even add a flag for if astrape was reached to instead add a "past the dam or at astrape" at the end
edit: flag not being for if you were at astrape when it happened, just a flag purely for if the character would even know where astrape is to begin with