User blog comment:Mckrongs/Monster Hunter 4 for the Nintendo 3DS/@comment-6050823-20130503220940/@comment-4517572-20130504074335

I think it looks like the ground is rising because of the camera angle. I've seen the same thing happen in another video; monsters can destroy the face of that mountain and part of the wall falls down.

It's just a cooler form of destructable terrain like TigrexJeff mentioned.