The Shape and Erosion of Pebbles

Adam Roth

It is an interesting question as to why pebbles are generally rounded. Why is this shape favored above others? In order to understand this, it is necessary to understand the erosion process. The first tool in this study is an objective method of describing the shape of a pebble. The problem is that it is difficult to get an accurate measurement of the boundary of a pebble.  Generally the data are too noisy or pixelated to get any accuracy. Towards this end we will take many pictures of the same pebble at various orientations in order to eliminate pixel noise. This noise is an artifact of the orientation of the sensor with respect to the object, so with enough pictures it should be possible to average out this noise. Once the shape of a pebble can be accurately determined, it is possible to see how the shape changes as pebbles erode. We will measure the initial shape of a pebble, then place it in a tumbler for a period of time, then measure the shape again. This will hopefully provide information about how the erosion process changes the shape of a pebble, and perhaps give a method for reconstructing an earlier shape from the present shape of a pebble. This would have applications in geology, and the method for reducing pixel noise could have applications in many fields.