We present a unified framework for understanding the compaction of colloidal gels under their own
weight. The dynamics of the collapse are determined by the value of the gravitational stress
g, as
compared to the yield stress
Y of the network. For
g <
Y, gels collapse poroelastically, and their rate of compression decays exponentially in time. For
g >
Y, the network eventually yields, leading to rapid
settling. In both cases, the rate of collapse is backflow limited, while its overall magnitude is determined
by a balance between gravitational stress and network elastic stress.