I don’t think those are side vents. If you are referring to the first picture, what you are seeing is the pyroclastic flow. The ash cloud collapses after the heat dissipates.
I was wondering about whether that could be what was happening, but the convergence looks much like the smoke is rushing towards the low pressure caused by the column of rising air, then it does like smoking falling away from the center. On the other hand, so many simultaneous side vents seems unlikely.
On second thought, they do all seem to be flowing towards the lowest points... I think you’re right.