ial within the bars, islands and floodplains that define their morphology. The world's largest rivers are characterized by remarkable variety in form and behavior (e.g., width, depth, number of channels, bar and island stability), which remain poorly understood. This study by Andrew Nicholas applies a new numerical model of water flow and sediment transport to show how the morphology of large sand-bed rivers is influenced by bed sediment mobility, bank erodibility, and rate of floodplain development. Simulations demonstrate that a wide range of river styles, including meandering, anabranching, and braiding, can occur over a relatively narrow range of environmental conditions. Results highlight the suspension of bed material as a key control on river morphology, which promotes an inverse relationship between bed sediment mobility and the degree of channel branching. Moreover, high mobility of bed and bank sediments is hypothesized to favor contrasting river styles, although both may be promoted by increasing river gradient. These results explain the inability of existing theory to predict the morphology of the world's largest rivers, and highlight the potential for investigating river-floodplain co-evolution using physics-based simulation models.
The fossil record of insect color illuminated by maturation experiments
Maria E. McNamara et al., School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK. Posted online 20 Feb. 2013; http://dx.doi.org/10.1130/G33836.1.
Structural coloration underpins communication strategies in many insects alive today, but its evolution is poorly understood. This stems, in part, from limited data on how color alters during fossilization. Maria E. McNamara and colleagues resolve this by using elevated pressures and temperatures to simulate the effects of burial on structurally colored cuticles of modern beetles. These expePage: 1 2 3 4 5 6 7 8 9 10 11 Related biology news :1
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