User blog comment:FairyRaven/Fairy Tail Chapter 391: Gray vs. Silver, Review and Commentary/@comment-4933386-20140705051946/@comment-7418318-20140705094533

We see the spell starting out as a small ice-crystal on the ground. If he cut off a pice of the ground (or just encased it in ice) he could have concealed the upward movement of the rubble with this growing effect.