You can strike the ground with your tail so hard it knocks other creatures down.
Prerequisites: Str 13, dragon, size Large or larger, Power Attack.
Benefit: You may, as a full-round action, strike a solid surface with your tail and create a shock wave that radiates out from your space and continues for a number of feet equal to 5 × your racial Hit Dice. Make a bull rush attack by rolling once regardless of how many creatures are in the radius. Every creature in the radius makes a Strength check and compares it to your roll. Those who fail their opposed checks are knocked down.
Special: Structures and unattended objects at least partially within the shock wave take damage equal to 1d6 + your Strength bonus.
Source: Draconomicon, page 73.