incise

"One way you can think about how rivers incise long term -- you need to be able to move sediment, and once you cross over some threshold, you can incise the river," Carr said.

"Over the course of a mountain belt developing, we're seeing differences in how rivers incise, or cut down into the bedrock, in the younger and older sections," said Julia Carr, lead author of the study who earned her doctorate in geosciences from Penn State in 2022.

During high flows after storms, these boulders may be fully mobile, and as they move, they help incise the river.

“These linear features mean the river is going to form in the same place every year, allowing the water to incise deeper,” Boghosian says.

The local artist uses a compass to incise tightly arrayed complementary lines into large sheets of black-painted plaster topped with glistening layers of graphite and varnish; the resulting pieces appear metallic and machine-tooled.