As two actions, you teleport entire chunks of the earth or stone 10 meters into the air, where they fall onto the targets below at a point within 20 meters. Each creature in a sphere centered on that point must make a Reflex saving throw.
On a failure, it takes 6d6 bludgeoning damage.
On a critical failure, it takes twice as much damage.
On a success, it takes half as much damage.
On a critical success, it takes no damage.
In addition, the ground in the affected area becomes difficult terrain until cleared. Each 1-meter square portion of the area requires at least 1 minute to clear by hand.
You can increase the damage by 2d6 for each additional mana expended.