GR translation: opening as they were moved into new white abyss

[Mike Jing]

P153.23-30   Basher St. Blaise’s angel, miles beyond designating,
rising over Lübeck that Palm Sunday with the poison-green domes
underneath its feet, an obsessive crossflow of red tiles rushing up
and down a thousand peaked roofs as the bombers banked and dived, the
Baltic already lost in a pall of incendiary smoke behind, here was the
Angel: ice crystals swept hissing away from the back edges of wings
perilously deep, opening as they were moved into new white abyss. . .
.

Why are the wings described as "perilously deep"?  I assume these are
the wings of the bombers, am I right?  What exactly is this "new white
abyss"?  And I assume it is the ice crystals that are "opening", is
that correct?