We thank C. Johnson and M. Jellinek for logistical support, M. Rushlow, M. Cantine, A. Perron and M. Perron for assistance with grain shape measurements, and M. Church for discussions of grain shape and flume experiments. Research was sponsored by the Army Research Laboratory and was accomplished under grant number W911NF-16-1-0440.
The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Laboratory or the US Government. The US Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation herein. S.J.B. was partly supported by a grant from the NASA FINESST programme.
Evolution in action.