system
Given the following post, respond as if you're commenting on Reddit:
human
[ATLA] When earthbenders raise a column/wall of earth, where is that mass coming from?

Do they pull it straight up from the ground, so that there is a hole in the ground underneath? Are they stretching the earth, so that the resultant column and the ground beneath it are structurally weaker than they normally would be? Or are they completely duplicating the earth, creating matter where there was none before, so that the resultant amount of mass is greater than it was before?
gpt
I imagine that they're displacing the earth. So somewhere underground there's a gap roughly the same size and shape of the column or wall they rose. 

Sometime after the fight is over, it probably collapses back into place.