A model is proposed for the behaviour of flow slides in loose, cohesionless materials in which the debris spreads out as a uniform sheet. Excess pore-fluid pressures are assumed to be generated, for example by undrained loading arising from the collapse of metastable structure, in the source area of the flow slide. Under the influence of these, the leading element of the debris moves downslope by basal sliding, consolidating as it does so by single, upward drainage. As a result, the pore pressure at the base of the element eventually decays to a value that brings the element to rest, hence defining the run-out of the flow slide. The model is applicable, in principle, to subaqueous and subaerial flow slides and to pore fluids consisting of water, gas, or both of these. The predictions of the model are tested against the observed behaviour and measured properties of the 1966 flow slide at Aberfan, South Wales. The results show that a sliding–consolidation model provides a possible mechanism for that event. Key words: Cohesionless material, loose metastable structure, partial liquefaction, excess pore-fluid pressure, basal sliding, consolidation, flow slide, acceleration, velocity, run-out.