Such is the force of your attack that the ground opens beneath your enemy and holds it down.

Encounter   ✦     Primal, Weapon
Standard Action      Melee weapon

Target: One creature

Attack: Strength vs. AC

Hit: 3[W] + Strength modifier damage, and the target is knocked prone and can't stand up until the end of your next turn.

  Earthstrength: You also slide the target a number of squares equal to your Constitution modifier.

Published in Player's Handbook 2, page(s) 164.