Historic logging site shows first human-caused bedrock erosion along an entire river

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April 15, 2019

Geologic time is supposed to be slow, and the most solid object should be bedrock. But new University of Washington research upends both concepts: Effects of logging show that human activity can significantly erode bedrock, causing geology to fast forward.
The study, published April 15 in the Proceedings of the National Academy of Sciences, focuses on the Teanaway River, a picturesque river in central Washington state.

The Teanaway River in fall 2018.Scott Christy/Flickr

“In the last century, we have more river incision in this area than expected. Something caused these rivers to start eroding a lot more,” said lead author Sarah Schanz, a former UW doctoral student who is now a postdoctoral researcher at Indiana University. “We know the Teanaway River has eroded into bedrock before, naturally — it has some terraces that are 1,800 years old. But this current cycle is anthropogenic, or human-driven.”

Exposed bedrock in the Teanaway River forms flutes and grooves — depressions where gravel gets trapped in a pothole and erodes it further. The oblong depressions are popular summer bathing spots.Sarah Schanz/Indiana University

Results show that practices related to logging caused bedrock incision of up to 2 meters (6 feet) along the riverbed. As much as a half of what had been a floodplain was transformed into a new terrace abutting the river.
“This is the first time that we’ve been able to pinpoint erosion into bedrock due to human action,” Schanz said. “Most rivers are eroding at about a tenth of a millimeter per year. This is about 100 times that amount.”
The discovery means this beautiful riverbank resulted from human action, not natural forces. It could change how geologists think about landscapes in other parts of the world, such as Taiwan, with its long history of intense human activity.

David Montgomery and doctoral student Vivian Leung study the bank of …

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