The team's findings, published in the journal Physical Review Fluids, shed light on one of the most fundamental questions in geomorphology: How do river rocks get their characteristically smooth, round shape?
The answer, it turns out, lies in the interplay of three forces: the force of the water flowing over the rocks, the force of the rocks colliding with each other, and the force of the rocks grinding against the riverbed.
"This is a problem that has been studied for centuries, but no one has ever been able to come up with a complete mathematical description of how it works," said Ian Walker, a professor of geophysics at the University of Texas at Austin's Jackson School of Geosciences and co-author of the study. "We're excited to be the first to do so."
The team's mathematical model is based on the observation that river rocks are constantly being broken down into smaller pieces by the force of the water flowing over them. These smaller pieces then collide with each other and with the riverbed, further breaking them down into even smaller pieces. Over time, this process of abrasion and attrition rounds off the sharp edges of the rocks and gives them their smooth, round shape.
The team's model also takes into account the fact that the rate at which rocks break down depends on their size and shape. Larger rocks are more resistant to abrasion than smaller rocks, and rocks with sharp edges are more likely to break than rocks with smooth edges.
"Our model is able to accurately predict the rate at which river rocks become round," Walker said. "This is a significant advance in our understanding of the geomorphic processes that shape our planet's landscapes."
The team's findings could have applications in a variety of fields, including engineering, geology, and environmental science. For example, the model could be used to design more efficient rock-crushing machines or to predict the rate of erosion in riverbeds.
"We're excited about the potential applications of our research," Walker said. "We believe that it could have a significant impact on a number of different fields."
