A quasi-two-dimensional method is presented for predicting liquefaction flow slides in a slope with saturated loose sand. The initial stresses at the start of the actual flow slide process are predicted assuming completely drained conditions during the gradual change in slope geometry caused by erosion or sedimentation. The condition for a flow slide is considered to be the presence of at least one sand element in a metastable stress state, i.e., a state in which the undrained response to any quick change in load, however small it may be, consists of a sudden large increase in pore pressure. The metastability of any sand element is predicted as a function of its constitutive properties, its location in the slope, and the slope geometry. The constitutive properties are derived from dry triaxial tests and basically describe the liquefiability (brittleness) of the sand. The metastability criterion for a soil element in a slope is different from that under triaxial loading. Flow slides observed in large-scale tests occurred at the conditions predicted with the model.Key words: loose sand, flow slides, liquefaction, collapse, slope instability.