Making River Rock Round

Downstream Upstream River RockFebruary 14, 2014 – Here is some interesting research. For centuries, geologists have recognized that the rocks that line riverbeds tend to be smaller and rounder further downstream. But these experts have not agreed on the reason these patterns exist. Abrasion causes rocks to grind down and become rounder as they are transported down the river. Does this grinding reduce the size of rocks significantly, or is it that smaller rocks are simply more easily transported downstream? A new study by the University of Pennsylvania’s Douglas Jerolmack, working with mathematicians at Budapest University of Technology and Economics, has arrived at a resolution to this puzzle. Contrary to what many geologists have believed, the team’s model suggests that abrasion plays a key role in upholding these patterns, but it does so in a distinctive, two-phase process. First, abrasion makes a rock round. Then, only when the rock is smooth, does abrasion act to make it smaller in diameter. “It was a rather remarkable and simple result that helps to solve an outstanding problem in geology,” Jerolmack said. Read more here.