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Erosion has a point -- and an edge, NYU researchers find

November 12, 2012

Erosion caused by flowing water does not only smooth out objects, but can also form distinct shapes with sharp points and edges, a team of New York University researchers has found. Their findings, which appear in the latest edition of the journal the Proceedings of the National Academy of Sciences (PNAS), reveal the unexpected ways that erosion can affect landscapes and artificial materials.

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.

"The main focus of this study was to understand how and why erosion makes these funny shapes," explained Leif Ristroph, a post-doctoral researcher at NYU's Courant Institute of Mathematical Sciences and one of the study's co-authors.

To explore these questions, the researchers designed an experiment, conducted in the Courant Institute's Applied Mathematics Laboratory, to replicate natural erosion. In it, the researchers submerged clay--shaped as balls or cylinders--into a 15-ft. long water tunnel. The apparatus was designed to continuously generate a uniform flow of water, which would allow 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," explained Ristroph. "In a sense, it works as a sculptor to naturally mold materials into new forms."
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The study's other co-authors were: Matthew Moore, a Courant post-doctoral fellow; Courant Professors Stephen Childress and Michael Shelley; and Jun Zhang, a professor at the Courant Institute and NYU's Department of Physics.

The research was supported by grants from the U.S. Department of Energy (DE-FG02-88ER25053) and the National Science Foundation (DMS-1103876, MRI-0821520).

New York University

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Related Erosion Reading:

Erosion: Changing Earth's Surface (Amazing Science)
by Robin Koontz (Author), Matthew Harrad (Illustrator)

Did you know that rain, waves, wind, snow, and ice can change the shape of Earth’s surface? They can create valleys, sea stacks, caves, and rock arches. Learn about the natural forces of erosion and how they shape the land. View Details


Cracking Up: A Story About Erosion (Science Works)
by Jacqui Bailey (Author), Matthew Lilly (Illustrator)

Describes the process of erosion and how water, ice, wind, and sun wear away at Earth's surface. View Details


Weathering and Erosion (Science Readers: Content and Literacy)
by Torrey Maloof (Author)

The Earth's surface is always changing. Learn how weathering and erosion constantly reshapes the earth through wind, water, and more! Even people can drastically change the earth's surface. With the help of easy-to-read text and bright, colorful images, this reader simplifies challenging scientific topics while keeping students engaged from cover to cover. This reader also includes instructions for an engaging science activity where students can see what happens when land erodes. A helpful glossary and index are also included for additional support. View Details


Erosion (Reading Essentials in Science)
by Virginia Castleman (Author)

Earth is changing every day as a result of erosion, and weather plays a major part. View Details


Erosion and Weathering (Rocks: The Hard Facts)
by Willa Dee (Author)

Discusses the different causes of erosion and weathering, how these phenomena create problems for people, and their role in the rock cycle. View Details


Soil Erosion and How to Prevent It (Everybody Digs Soil)
by Natalie Hyde (Author)

Looks at the processes of weathering, erosion, and deposition, and how they affect plant and animal life. View Details


Erosion: The Psychopathology of Self-Criticism
by Golan Shahar (Author)

Self-criticism is a personality trait that has been implicated in a wide range of psychopathologies and developmental arrests. Defined as the tendency to set unrealistically high standards for one's self and to adopt a punitive stance towards the self once these standards are not met, self-criticism is both active and cyclical. Self-critics actively create the social-interpersonal conditions that generate their distress, and their distress itself exacerbates self-criticism.

Erosion offers a comprehensive treatment of self-criticism based in philosophy, developmental science,... View Details


Dirt: The Erosion of Civilizations
by David R. Montgomery (Author)

Dirt, soil, call it what you want―it's everywhere we go. It is the root of our existence, supporting our feet, our farms, our cities. This fascinating yet disquieting book finds, however, that we are running out of dirt, and it's no laughing matter. An engaging natural and cultural history of soil that sweeps from ancient civilizations to modern times, Dirt: The Erosion of Civilizations explores the compelling idea that we are―and have long been―using up Earth's soil. Once bare of protective vegetation and exposed to wind and rain, cultivated soils erode bit by bit, slowly enough... View Details


After the Fact: The Erosion of Truth and the Inevitable Rise of Donald Trump
by Nathan Bomey (Author)

This trenchant analysis examines the many ways our society's increasingly tenuous commitment to facts laid the groundwork for Donald Trump's rise to power.

Award-winning journalist Nathan Bomey argues that Trump did not usher the post-truth era into being. He was its inevitable outcome. Bomey points to recent trends that have created the perfect seedbed for spin, distortion, deception, and bald-faced lies: shifting news habits, the rise of social media, the spread of entrenched ideologies, and the failure of schools to teach basic critical-thinking skills

The evidence... View Details


Erosion
by Alexander Olson (Author)

As life erodes away in a world devastated by an asteroid, Dustin struggles to survive. He fights against cannibals, crazed preachers, elderly people with guns and the constant need for water, all while trying to keep a tiny infant alive.
When the baby gets kidnapped, Dustin must decide whether to give chase or give up, and take the easier path to survival.

View Details

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