Knickpoint evolution in a vertically bedded substrate, upstream-dipping terraces, and Atlantic slope bedrock channels

Abstract

Research Article| March 01, 2007 Knickpoint evolution in a vertically bedded substrate, upstream-dipping terraces, and Atlantic slope bedrock channels Kurt L. Frankel; Kurt L. Frankel 1Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, Pennsylvania 18015, USA Search for other works by this author on: GSW Google Scholar Frank J. Pazzaglia; Frank J. Pazzaglia 1Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, Pennsylvania 18015, USA Search for other works by this author on: GSW Google Scholar Jordan D. Vaughn Jordan D. Vaughn 1Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, Pennsylvania 18015, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Kurt L. Frankel 1Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, Pennsylvania 18015, USA Frank J. Pazzaglia 1Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, Pennsylvania 18015, USA Jordan D. Vaughn 1Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, Pennsylvania 18015, USA Publisher: Geological Society of America Received: 10 Jan 2006 Revision Received: 11 Oct 2006 Accepted: 19 Oct 2006 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 GEOLOGICAL SOCIETY OF AMERICA GSA Bulletin (2007) 119 (3-4): 476–486. https://doi.org/10.1130/B25965.1 Article history Received: 10 Jan 2006 Revision Received: 11 Oct 2006 Accepted: 19 Oct 2006 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Kurt L. Frankel, Frank J. Pazzaglia, Jordan D. Vaughn; Knickpoint evolution in a vertically bedded substrate, upstream-dipping terraces, and Atlantic slope bedrock channels. GSA Bulletin 2007;; 119 (3-4): 476–486. doi: https://doi.org/10.1130/B25965.1 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 We conducted flume experiments to investigate the nature of knickpoint and bedrock channel longitudinal profile evolution for a channel reach underlain by a vertically bedded substrate of alternating resistance. This research was motivated by the presence, behavior, and apparent persistence of impressive knickpoints formed in steeply dipping or steeply foliated bedrock in Atlantic slope drainages of the Appalachian Mountains. The experiments were carried out in a 10-m-long wooden-box flume filled with a very fine– to medium-grained sand alluvial substrate and a single, 30-cm-wide ridge of vertically oriented, lacustrine silt-clay varves designed to simulate a bedrock channel reach. Numerous control experiments established a stable meandering channel form and transport gradient, from which knickpoints were produced by a single, instantaneous base-level fall at the channel mouth. Knickpoint evolution in the alluvial material downstream of the bedrock reach was dominated by inclination of the knick-point face; this resulted in a rapid transition from a waterfall at the point of base-level fall to a broad, convex zone spanning the entire lower alluvial channel reach. A waterfall and plunge pool reformed at the contact between the lower alluvial reach and the simulated bedrock ridge where the knickpoint shortened and steepened. The knickpoint then migrated upstream through the bedrock reach by a combination of parallel retreat and vertical channel incision. The knickpoint evolution process resulted in the formation of upstream-dipping strath terraces, an uncommon landform possibly present in the Holtwood Gorge of the Susquehanna River. As base-level fall effects were transmitted to the alluvial channel above the bedrock reach, a complex channel response, accompanied by pulses of sediment, alternately buried and excavated the bedrock reach. These results illustrate the complex behavior associated with knickpoint evolution, the unsteadiness of the bedrock channel erosion process, and the significant lag times that may exist in natural fluvial systems that are in the process of adjusting to base-level fall. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.