When stock gap up, it usally has high volume, if you see low volume during the upcoming consolidation cycle, and stock showing the behavior we talk about here, it is very likely that retail buyers trying to sell at gap (for the reason described above), and instituion are accumulating
However, sometimes, you see increasing high volume during the consolidation phase, that could be a sign that institution are secretely running away
In IWM's case, this looks more like former than latter
