Fracture density and grain size controls on the relief structure of bedrock landscapes

Research Article| February 23, 2018 Fracture density and grain size controls on the relief structure of bedrock landscapes Roman A. DiBiase; Roman A. DiBiase * 1Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA2Earth and Environmental Systems Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA *E-mail: rad22@psu.edu Search for other works by this author on: GSW Google Scholar Matthew W. Rossi; Matthew W. Rossi 3Earth Lab, University of Colorado, Boulder, Colorado 80309, USA Search for other works by this author on: GSW Google Scholar Alexander B. Neely Alexander B. Neely 1Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Roman A. DiBiase * 1Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA2Earth and Environmental Systems Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA Matthew W. Rossi 3Earth Lab, University of Colorado, Boulder, Colorado 80309, USA Alexander B. Neely 1Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA *E-mail: rad22@psu.edu Publisher: Geological Society of America Received: 08 Sep 2017 Revision Received: 19 Dec 2017 Accepted: 05 Feb 2018 First Online: 23 Feb 2018 Online Issn: 1943-2682 Print Issn: 0091-7613 © 2018 Geological Society of America Geology (2018) 46 (5): 399–402. https://doi.org/10.1130/G40006.1 Article history Received: 08 Sep 2017 Revision Received: 19 Dec 2017 Accepted: 05 Feb 2018 First Online: 23 Feb 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Roman A. DiBiase, Matthew W. Rossi, Alexander B. Neely; Fracture density and grain size controls on the relief structure of bedrock landscapes. Geology 2018;; 46 (5): 399–402. doi: https://doi.org/10.1130/G40006.1 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 SocietyGeology Search Advanced Search Abstract Quantifying how rock properties influence landscape evolution is an outstanding challenge that confounds attempts to generalize relationships between topography and erosion rate. Defining proxies for rock strength at the landscape scale is difficult because hillslope and channel erosion processes differ in their sensitivity to rock material properties. Here we show how the fracture density of bedrock hillslopes and the related grain size distribution of sediment delivered to channels exert a first-order control on topography and erosion rate in steep, rocky landscapes. We analyzed two sites in southern California, USA, that share similar lithology and hydroclimate, but that differ in tectonic setting, bedrock fracture density, sediment grain size, and relief structure. Multi-scale analysis of lidar point clouds reveals a systematic contrast in mean slope and relief of bedrock cliffs, consistent with higher fracture density leading to a reduction in rock mass strength, but colluvial slopes are invariant across both landscapes. The relation between fluvial relief and erosion rate indirectly records differences in fracture density via the grain-size distribution observed in channels. By increasing the fluvial incision threshold, coarser sediment decreases the frequency of erosive floods. Erosion thresholds also appear to control the extent of headwater colluvial channel networks likely carved by debris flows. Taken together, these results show how increased bedrock fracturing alters drainage density and systematically reduces landscape-scale topographic relief. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.