A process whereby some sort of order arises from an initially disordered system, a process arising from the interactions within the system. For example, distinctive zones of land use may arise within a city though they have not been formally designated as such. ‘Morphodynamic systems often display a sequence of positive feedback driving the system towards a new state, followed by negative feedback, which stabilizes the system, resulting in equilibrium. This is referred to as self-organization. The result of this process is a rather orderly arrangement of sediments and landforms’ (Masselink in J. Holden (2012) p. 447). Examples include the formation of evenly spaced, nearly uniform ripples on sand dunes or stream beds, or of patterned ground in periglacial landscapes. ‘Nonlinear, dissipative interactions among the small- and fast-scale constituents of a system give rise to order at larger spatial and longer temporal scales’ (Phillips (2003) PPG 27, 1). ‘Those not convinced by arguments of self-organisation and inherent behaviour as an explanation in itself commonly ask the mechanism of the changes. Even for those who support the theory, questions still arise of how the self-organisation takes place and how the changes are communicated from one part of the system to another such that order emerges’ (Hooke (2007) Geomorph. 91, 3–4).

Self-organized criticality describes a system in dynamic equilibrium near a threshold condition. The concept arises from Bak et al. (1987) Phys. Rev. Letts 59, 4, who develop a simple cellular automaton model in which sand is added, grain by grain, to a surface to form a pile. When local slopes become too steep a collapse occurs, moving sediment to neighbouring cells, which too can collapse if the adjusted slopes are too steep. See Coulthard and Van De Wiel (2007) Geomorph. 91, 3–4.