How do you get rid of the rocks blocking Virizion in Pokemon Black?

You don't need to get rid of the rocks blocking Virizion in Pokemon Black!

Virizion is not found in Pokemon Black. It is a legendary Pokemon exclusive to Pokemon White.

If you're playing Pokemon White, you'll need to find the "Legendary Obelisk" located on Route 13. This Obelisk allows you to summon Virizion, but you'll need to have already defeated the Elite Four and become the Pokemon League Champion.