Since it's not specified, there's really no reason to assume that rather than ruling the opposite, which to me seems the more likely choice for a GM, since that makes the ability not so abusable.
Column often implies a cylindrical or rounded shape that taper as they rise; all of the descriptions in the wikipedia article on columns mention cylinders. It also implies a single rising object with space around it, not a bunch of solid blocks
As a 5-10' wall, the great wall of china this is not (which ranges from 5-8 meters high, 16.4 to 26.2 feet).