1. not passable; not allowing passage over, through, along, etc.: Heavy snow made the roads impassable.
2. unable to be surmounted: an impassable obstacle to further negotiations.
There has been a lot of hype this year citing data which is suggesting that we’ll be able to navigate the Northwest Passage and some even so bold as to suggest a completely ice free Arctic Sea. You could say: “A picture is always worth 1000 data points.”
I’d say “impassable” fits this picture pretty well: