The flow of liquefied clay. Debris of all sizes, including large blocks of rock, may be transported by mud flows. In a study of northern Italy, Luino (2005) Geomorph. 66, 1–4 finds that mud flows in small drainage basins are usually triggered when the rainfall has reached a value equal to 10–20% of the local mean annual rainfall (MAR). Mud flows in larger basins are triggered when rainfall is equivalent to 15–30% of the local MAR.