NYU (US) — Erosion caused by flowing water not only smoothes out objects, but can also form distinct shapes with sharp points and edges.

The impact of erosion is widely recognized by environmentalists and geologists, but less clear is how nature’s elements, notably water and air, work to shape land, rocks, and artificial structures, often resulting in unusual formations.

“Water acts tangentially to the surface of objects and skims off material to create these unique shapes,” explains Leif Ristroph. “In a sense, it works as a sculptor to naturally mold materials into new forms.” (Credit: Phil’s 1stPix/Flickr ^[1])

A new study published in Proceedings of the National Academy of Sciences ^[2] reveals the unexpected ways that erosion can affect landscapes and artificial materials.

“The main focus of this study was to understand how and why erosion makes these funny shapes,” explains Leif Ristroph, a post-doctoral researcher at New York University’s Courant Institute of Mathematical Sciences and one of the study’s co-authors.

For an experiment designed to replicate natural erosion, Ristroph and colleagues submerged clay—shaped as balls or cylinders—into a 15-foot-long water tunnel. The apparatus was designed to continuously generate a uniform flow of water, which allowed the researchers to observe how erosion shapes an entire object.

What they found was water flow acts as a shearing force—not unlike a nail file—against objects, working them into specific shapes. Starting from a clay ball, the flowing water sheared the sides away, producing a cone with a pointed face.Likewise, the clay cylinder was sculpted into a triangular shape.

The researchers then sought to confirm these findings by replicating the experiment using a computer model. These results were consistent with the experimental findings, revealing in a computer simulation how the shape was maintained as the body eroded away.

“Water acts tangentially to the surface of objects and skims off material to create these unique shapes,” explains Ristroph. “In a sense, it works as a sculptor to naturally mold materials into new forms.”

The US Department of Energy and the National Science Foundation supported the research.

Source: New York University ^[3]