Causes and Effects of Noise in Landscape Dynamics

Jerolmack D.J. Causes and Effects of Noise in Landscape Dynamics. Eos, Vol. 92, No. 44, 1 November 2011.

Geomorphology, the study of landscape form and change, is at a crossroad. Quantification of patterns on Earth’s surface has revealed surprising and robust order. Transport equations rooted in physics that relate material flux of sediment to environmental drivers have been derived and are capable of simulating realistic-looking topography [Dietrich et al., 2003]. Yet despite this rapid progress and an explosion of interest in the field, scientists are unable to predict sediment transport rates in rivers to better than an order of magnitude—they can only qualitatively anticipate the response of landscapes to land use or climatic changes. In addition, some argue that the sedimentary archive of landscape evolution is dominated by randomness [Sadler and Strauss, 1990], calling into question researchers’ ability to reconstruct environmental change from the rock record. A major obstacle to progress is the lack of understanding of the nature and origins of “noise” in sediment transport. “Noise” here refers to the seemingly random or inexplicable fluctuations in transport rate that can occur without any external perturbation. Transport noise can obscure the relations between cause and effect in landscape evolution. Two key questions help to focus research efforts: (1) How do noisy dynamics arise in a steady environment? (2) How can robust, ubiquitous patterns persist in a noisy environment? Addressing these questions will require the adoption of theoretical and experimental approaches that are outside the realm of traditional geomorphology.