Abstract The formation of eddies by dense overflows in stratified water is examined by laboratory experiments. The dense fluid initially flows down the slope but turns (under the influence of rotation) to flow along the slope. The inviscid alongslope flow is continuously drained by a viscous Ekman layer that flows more directly downslope. In some cases this Ekman layer flow becomes unstable to growing waves. Under certain conditions, strong cyclonic vortices form in the ambient fluid above the alongslope flow due to vortex stretching, causing the dense fluid to break up into a series of domes. There are three main mechanisms for this: first, the initial downslope flow of the current (before it turns under the influence of rotation) may take “captured” upper-layer fluid with it out into deeper water; second, adjustment of the current to geostrophic balance stretches the fluid column above the current; and, finally, the continuous viscous draining from the current (and later from the domes) also causes stre...