How River Rocks Round: Resolving the Shape-Size Paradox

Gabor Domokos, Douglas J Jerolmack, Andras Á Sipos and Ákos Török

PLOS ONE, 2014, vol. 9, issue 2, 1-7

Abstract: River-bed sediments display two universal downstream trends: fining, in which particle size decreases; and rounding, where pebble shapes evolve toward ellipsoids. Rounding is known to result from transport-induced abrasion; however many researchers argue that the contribution of abrasion to downstream fining is negligible. This presents a paradox: downstream shape change indicates substantial abrasion, while size change apparently rules it out. Here we use laboratory experiments and numerical modeling to show quantitatively that pebble abrasion is a curvature-driven flow problem. As a consequence, abrasion occurs in two well-separated phases: first, pebble edges rapidly round without any change in axis dimensions until the shape becomes entirely convex; and second, axis dimensions are then slowly reduced while the particle remains convex. Explicit study of pebble shape evolution helps resolve the shape-size paradox by reconciling discrepancies between laboratory and field studies, and enhances our ability to decipher the transport history of a river rock.

Date: 2014
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Persistent link: https://EconPapers.repec.org/RePEc:plo:pone00:0088657

DOI: 10.1371/journal.pone.0088657

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