The Collaborative International Dictionary of English v.0.48:

Zastrugi \Zas*tru"gi\, n. pl.; sing. -ga. [Russ. zastruga
   furrow made on the shore by water.]
   Grooves or furrows formed in snow by the action of the wind,
   and running parallel with the direction of the wind. This
   formation results from the erosion of transverse waves
   previously formed.
   [Webster 1913 Suppl.]