Burrow

The target can breathe underground while burrowing. If you're 3rd tier, the burrow speed increases to 20 feet through sand, soil, or gravel, and to 10 feet through stone. At 6th tier, these speeds increase to 30 feet and 15 feet respectively. At 9th tier, these speeds increase to 40 feet and 20 feet.

Augmented (3rd): If you expend two uses of mythic power, the burrowing creature may leave behind an open tunnel with a diameter equal to half its space. When the spell's effect ends, this tunnel closes up immediately.