Many factors can affect a waterfall’s formation – changes in bedrock structure, tectonic shifts, and glacial motion, to name a few. But a new study suggests that some waterfalls may be self-forming. Using a lab-scale experiment, researchers created a homogeneous “bedrock” out of polyurethane foam, which they eroded with a combination of constant water flow and particulates. Even without external perturbations, the flow carved out a series of steps. 

As a pool deepened, particles built up inside, armoring the bed against further erosion. But further downstream, the chute continued to erode, steepening the area between them until a waterfall formed. On the timescale of the experiment, the waterfalls lasted only 20 minutes or so, but that’s equivalent to up to 10,000 years in geological time. (Image credit: M. Huey; research credit: J. Scheingross et al.; via EOS News; submitted by Kam-Yung Soh)