Sources of nonlinearity and complexity in geomorphic systems

Abstract

Nonlinearity is common in geomorphology, though not present or relevant in every geomorphic problem. It is often ignored, sometimes to the detriment of understanding surface processes and landforms. Nonlinearity opens up possibilities for complex behavior that are not possible in linear systems, though not all nonlinear systems are complex. Complex nonlinear dynamics have been documented in a number of geomorphic systems, thus nonlinear complexity is a characteristic of real-world landscapes, not just models. In at least some cases complex nonlinear dynamics can be directly linked to specific geomorphic processes and controls. Nonlinear complexities pose obstacles for some aspects of prediction in geomorphology, but provide opportunities and tools to enhance predictability in other respects. Methods and theories based on or grounded in complex nonlinear dynamics are useful to geomorphologists. These nonlinear frameworks can explain some phenomena not otherwise explained, provide better or more appropriate analytical tools, improve the interpretation of historical evidence and usefully inform modeling, experimental design, landscape management and environmental policy. It is also clear that no nonlinear formalism (and, as of yet, no other formalism) provides a universal meta-explanation for geomorphology. The sources of nonlinearity in geomorphic systems largely represent well-known geomorphic processes, controls and relationships that can be readily observed. A typology is presented, including thresholds, storage effects, saturation and depletion, self-reinforcing feedback, self-limiting processes, competitive feedbacks, multiple modes of adjustment, self-organization and hysteresis.

Criteria to Distinguish Between Periglacial, Proglacial and Paraglacial Environments

“…Holling suggests that all systems consist of adaptive cycles which exist at a range of spatial scales. The term adaptive is self-evident in ecological systems; in geomorphic systems we often speak of self-regulating systems (Phillips 2003). Adaptive cycles are defined as consisting of four phases, namely exploitation, conservation, release and reorganization.…”

Suspended sediment transport dynamics in rivers: Multi-scale drivers of temporal variation

“…Fine organic and inorganic material erode from land surfaces, flow downhill to a river and are then transported downstream as suspended sediment. However, research has increasingly highlighted the stochastic and variable nature of each stage of this basic process (Phillips, 2003). In fact, it is this complexity in the field-catchment-river sediment transfer system that makes estimation of the provenance, transport and deposition of sediment in rivers so challenging (Gao, 2008;Poulenard et al, 2009;Rickson, 2014;Sun et al, 2015;Zhang et al, 2013;Zheng et al, 2012).…”

Naturalness and Place in River Rehabilitation

“…Historical imprints, off-site (lagged) disturbance responses, and complex response (among other factors) ensure that rivers seldom behave as linear cause-effect, equilibrium systems (Phillips 2003). System specific attributes shape the range of potential future pathway(s) of adjustment.…”