Ruptures of tailing deposits can exhibit flow-like behavior and cause major disasters. An extensive mass of tailings can be transported over large distances at high velocity and flood downstream villages, resulting in the loss of lives and huge property losses. We present a series of flume tests to observe the process of tailing slope failure when subjected to a water flow. Progressive flow slides were observed in a range of tailing deposits with varying relative densities, in which hydraulic conductivity reduced with increasing relative density. The generation of pore pressure caused rupture for very loose and loose deposits, and is evident in acoustic emission signals. The water inflow into dense slopes is slower due lower hydraulic conductivity, resulting in successive sliding starting at the toe and progressing within the soil mass. A relative density of 0.35 is a transitional density from a sudden overall failure to a progressive failure.Ruptures of tailing deposits can exhibit flow-like behavior and cause major disasters. An extensive mass of tailings can be transported over large distances at high velocity and flood downstream villages, resulting in the loss of lives and huge property losses. We present a series of flume tests to observe the process of tailing slope failure when subjected to a water flow. Progressive flow slides were observed in a range of tailing deposits with varying relative densities, in which hydraulic conductivity reduced with increasing relative density. The generation of pore pressure caused rupture for very loose and loose deposits, and is evident in acoustic emission signals. The water inflow into dense slopes is slower due lower hydraulic conductivity, resulting in successive sliding starting at the toe and progressing within the soil mass. A relative density of 0.35 is a transitional density from a sudden overall failure to a progressive failure.