Barrier of Boreal Frost

You form an intricate structure of ice, such as a wall of bricks made of packed snow or a screen of enormous icicles. This has the effect of a spell with a spell rank equal to half your level rounded up. It can only be a wall (not a hemisphere), and you choose whether the ice is transparent or opaque. The wall lasts until the end of your next turn, but you can Sustain it up to 1 minute.