The shape and erosion of pebbles

We propose to characterize the shapes of flat pebbles in terms of the statistical distribution of curvatures measured along the pebble contour. This is demonstrated for the erosion of artificial pebbles in a controlled laboratory apparatus, as well as for rip-up clasts from the tidal flats of the Mt.-Saint Michel bay. Photographs at various stages of erosion are analyzed, and compared with models. We find that the curvature distribution complements the usual measurement of aspect ratio, and is more incisive for testing models. Furthermore, it connects naturally to erosion processes that are typically faster at protruding regions of high curvature.