hard to say. maybe the outskirts near gresham but I think a blast to the south would not damage portland significantly. our water supply from bull run might be vulnerable. if all the ice on hood melted immediately, where would it go? I would guess hood, salmon and sandy river watersheds. rainier ice melt seems like much more of a threat to major metro areas, where they've found all those twisted stumps buried in the backyards of seattle's suburbia