A mud flow, detrital flow or mud, is the fastest (over 80 km/h) and most fluid type of landslide. It consists of a flow "Cave (geology)") with a high concentration of detrital materials, which move towards the valleys with speeds that can reach and, in some cases, exceed 10 m/s. The transported material has a very variable granulometry, and a singular phenomenon frequently manifests itself with successive waves ("pulsations") due to the temporary obstruction of the transport channel. These detrital flows are phenomena widespread in almost all climatic regions, and are of notable importance both for their influence on the morphological evolution of the hydrographic basins in which they occur, and for the potential risk that they represent, especially in mountainous areas, due to their high destructive capacity. In these areas, water availability increases suddenly, commonly due to intense precipitation (mainly rain, sleet, and snow), which can cause increased water runoff down slopes, which in turn drags and transports large amounts of debris that will then be incorporated into the mudflow.

Detrital flows consist of mixtures of fine materials (sand, silt and clay) and coarser materials (gravel), containing a variable amount of water, which is added from plant debris. Thus, a muddy mass is formed in aqueous suspension "Suspension (chemistry)") that spreads as a single body, without separation between the solid phase and the liquid phase. It is a non-Newtonian fluid characterized by a variation in resistance to deformation that is non-linearly proportional to the rate of angular deformation. This determines a very high erosive capacity typical of these phenomena.