Can only be cast in the Underdark

You touch the ground beneath you and cause it to vibrate. Each creature that is burrowing below the ground's surface in a 40-foot cube centered on the point you touch must make a Dexterity saving throw. On a failure, a creature takes [roll]4d6[/roll] bludgeoning damage and has its movement speed halved until the end of its next turn. On a successful save, a creature takes half as much damage and its movement speed is unaffected. You briefly learn the location of a creature that takes damage from this spell, but not its identity.