Tailings are the fine-grained residue of mineral processing. Their volume usually exceeds the volume of the recovered minerals by several orders of magnitude. Because they contain large amounts of water, they must be stored behind embankments called tailings dams. The embankments are constructed with the steepest possible slopes to reduce cost, and are often constructed using the coarse fraction of the tailings. Thus tailings dams have some similarity to hydraulic fill dams, and a number of spectacular failures of tailings dams have occurred.
This photo shows a failure of a tailings dam retaining gypsum tailings in Florida. It can be seen that the wet gypsum tailings flowed like a viscous liquid when the dam failed.
This tailings dam in South Africa retained tailings from a platinum mine. Note the very flat slope formed by the tailings as they came to rest, indicating their very low shear strength.
This photo was taken after failure of a carbide lime tailings pond near Louisville, Kentucky. The tailings were so wet and weak that the surface after the failure was almost horizontal.