Rates and mechanisms of bedrock incision and strath terrace formation in a forested catchment, Cascade Range, Washington

Research Article| May 01, 2016 Rates and mechanisms of bedrock incision and strath terrace formation in a forested catchment, Cascade Range, Washington Brian D. Collins; Brian D. Collins † 1Department of Earth and Space Sciences and Quaternary Research Center, University of Washington, Seattle, Washington 98195-1310, USA †bcollins@uw.edu Search for other works by this author on: GSW Google Scholar David R. Montgomery; David R. Montgomery 1Department of Earth and Space Sciences and Quaternary Research Center, University of Washington, Seattle, Washington 98195-1310, USA Search for other works by this author on: GSW Google Scholar Sarah A. Schanz; Sarah A. Schanz 1Department of Earth and Space Sciences and Quaternary Research Center, University of Washington, Seattle, Washington 98195-1310, USA Search for other works by this author on: GSW Google Scholar Isaac J. Larsen Isaac J. Larsen 2Department of Geosciences, University of Massachusetts, Amherst, Massachusetts 01003-9297, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2016) 128 (5-6): 926–943. https://doi.org/10.1130/B31340.1 Article history received: 17 Apr 2015 rev-recd: 15 Oct 2015 accepted: 03 Dec 2015 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Brian D. Collins, David R. Montgomery, Sarah A. Schanz, Isaac J. Larsen; Rates and mechanisms of bedrock incision and strath terrace formation in a forested catchment, Cascade Range, Washington. GSA Bulletin 2016;; 128 (5-6): 926–943. doi: https://doi.org/10.1130/B31340.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Measurements of channel bed and bank incision into bedrock coupled with mapping and radiocarbon dating of strath terraces in the West Fork Teanaway River, Washington, provide insight into rates and mechanisms of river incision and strath terrace formation in a forested landscape. The West Fork drains 102 km2 of the slowly exhuming southeastern North Cascade Range, and it is rapidly eroding its bed and creating strath terraces in its lower reach. Minimum vertical incision, measured annually relative to nails embedded in the streambed, was greater in the seasonally exposed, weathering-dominated, high-flow channel (mean = 10.9 mm yr–1) than in the perennially wet, abrasion-dominated, low-flow channel (3.8 mm yr–1), documenting unsteady lowering of the channel margin. Ages of radiocarbon-dated materials from alluvium on strath terraces, 0.1 m to 5.4 m above the water surface, suggest three episodes of strath abandonment at maximum ages of ca. A.D. 830, A.D. 1560, and A.D. 1890, and average incision rates of 1.3 mm yr–1, 1.4 mm yr–1, and 7.4 mm yr–1 for the oldest to youngest surfaces, respectively. Weathering-promoted vertical incision in the high-flow channel provides a mechanism for "top-down" rapid lateral strath planation in which scour of alluvium on incipient strath terraces incorporates the surface into the high-flow channel, allowing rapid removal of bedrock weathered during wetting and drying cycles. Relationships among channel width, channel confinement by bedrock terrace risers, modeled bankfull shear stress, and alluvial bed cover suggest that rapid channel widening could also internally limit vertical incision by slowing incision as shear stresses decline and more alluvium is retained on the bed. The timing of the most recent (ca. A.D. 1890) strath abandonment corresponds with historical anthropogenic removal of fluvial wood, suggesting that the relative abundance of fluvial wood may influence episodes of vertical bedrock incision by affecting the retention of alluvium on streambeds. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.