by Maarten G. Kleinhans, William J. McMahon and Neil S. Davies
Meandering rivers are an iconic geomorphic form, recognized since antiquity (Gürbüz and Kazancı 2019) and familiar to most students of geoscience. It is thus both surprising and significant that a comprehensive and unequivocal definition of river meandering is hard to provide. Ambiguity in the definition of what constitutes a meandering river has resulted in sometimes mutually exclusive explanations for the phenomenon, often arising because competing explanations have flexible demarcations of the term ‘river meandering’. The uncertainty concealed within the name ‘meandering’ stems from several angles. Firstly, many features that are part and parcel of the phenomenon (Fig. 1) are also defined as different patterns within other kinds of landscapes surrounding them. Secondly, there is a continuum of channel forms that are transitional between other planforms (e.g. Leopold and Wolman 1957; Parker 1976; Ferguson 1987; Kleinhans 2010), and the bracket in this continuum that may be considered true meandering rivers can be only inexactly delineated. Thirdly, the distinction from other kinds of channels with bends is often unclear, and the pattern bears similarity with other phenomena such as capillary flows (Davies and Tinker 1984), channels on glaciers (Marston 1983), channels on intertidal mud flats (Fagherazzi et al. 2004; Kleinhans et al. 2009), sinuous ridges on Mars (Williams et al. 2013; Cardenas et al. 2022), lunar rilles (Hurwitz et al. 2013) and channels on Titan (Gilliam and Lerman 2016), lava tubes (Orr et al. 2015), channels embedded in mud (Kleinhans et al. 2009; Candel et al. 2021), and both submarine (Corney et al. 2006; Deptuck et al. 2007) and bedrock channels (Seminara 2006). Fourthly, if we seek to answer the question ‘what are the causes of meandering?’, we clearly require that ‘meandering’ is understood to be a set of properties. Yet such properties themselves require clear definition: do they need to have a single common cause, or can they emerge from fundamentally different underlying physical mechanisms?