......but as Mr. Lang took me on the Téléphérique for the first time, it became clear this mountain was unlike any I’d ever seen. A foot of new snow had fallen the night before, and spindrift whipped off La Meije, a sea of icy blue glaciers pocked by crevasses and cliffs unfurling down its flanks.
I couldn't figure out what to understand from this statement: spindrift whipped off La Meije what does spindrift do to La Meije? Or is it the spindrift that's the subject?
And my other question is how should I understand ...unfurling down its flanks? What I understand is a sea of icy blue glaciers pocked by crevasses and cliffs are presenting their entity on La Meije's flank's downside. but I'm not sure.