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

ScienceDaily | 4/15/2019 | Staff
Click For Photo: https://www.sciencedaily.com/images/2019/04/190415154702_1_540x360.jpg

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.

"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."

Results - Practices - Bedrock - Incision - Meters

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."

Discovery - Riverbank - Action - Forces - Geologists

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.

The study began 20 years ago when co-author Brian Collins, a UW senior lecturer in river geology, was curious why there was so much exposed bedrock in the Teanaway.

Collins - River - Terraces - Structures - River

Collins also noticed unusual river terraces, the stepped structures along the river bank resulting from cycles of the river flooding and then running more quickly, cutting a new channel deeper into the sediment. He led a 2016 study that calculated short-term changes in the Teanaway's western fork and suggested logging may have caused the river to cut a new channel.

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