Acoustic backscatter images obtained at 107 and 200 kHz of surge-type turbidity currents resulting from mine tailing discharge are presented. Excess densities in the head of the order of 100 kg m-3 are estimated from differences in acoustic backscatter intensity and in the amplitude of the bottom-reflected signal. These excess densities are comparable to estimates based on surge height and speed, the speed being determined by assuming a universal head shape. Unlike gravity current surges from an impulsively started steady source, the surge-type turbidity flows consist of a high concentration slug of short duration followed by a longer-lived wake in which sediment concentrations are lower by 2--3 orders of magnitude. The profile of the high concentration slug resembles those for density slugs on small bottom slopes obtained in laboratory experiments. Discrete scatterers, probably fish, are observed to avoid the surges. ¿American Geophysical Union 1987