I was looking at some other US-Asia flights on flightaware.com yesterday, and did find some route ranges on certain flights. For example, CX883 and CX885 (LAX-HKG) both are making stops at ICN. Usually, they fly near ANC to get to flight route R218, but one flew further south and then go back North after ANC; the other basically fly along the shore on a more Northern routing.

And looking at today's flights, seem like a lot of West Coast - Asia flights are flying a more southerly route. Not sure if it's just wind or if the volcano plays any part.