Quick clays are sensitive late-glacial and postglacial marine- and brackish-water sediments. Salt removal has decreased their remolded strength, such that, if disturbed, they behave as a liquid. Cementation by nano-sized particles of iron oxides at particle contacts may increase the sensitivity of quick clays in parts of the St. Lawrence Basin. Quick clay landslides are of two main types – stepwise and uninterrupted. In stepwise landslides, sufficient failed material liquefies that the debris from each step flows away from the slide scarp, leaving an unsupported unstable slope that, in turn, fails and flows away. Uninterrupted landslides require advance of the failure plane away from the riverbank at a rate sufficient to produce a continuous series of failing slices and continuous flow of the debris away from the scarp and along the river valley. As debris clogs the valley or loses momentum for any reason, the advance of the failure front slows down and soon stalls. For the end member of the uninterrupted category, the flakeslide, the failure plane advances so rapidly that a large area commences flow as a unit, breaking into subunits as it moves. Because quick clay development involves chemical change, appropriate chemical treatments should be effective and efficient in diminishing landslide risk.