Equivalence of abrupt grain-size transitions in alluvial rivers and eolian sand seas: A hypothesis

Abstract

Research Article| August 01, 2010 Equivalence of abrupt grain-size transitions in alluvial rivers and eolian sand seas: A hypothesis Douglas J. Jerolmack; Douglas J. Jerolmack * 1Department of Earth and Environmental Science, University of Pennsylvania, 240 S. 33rd Street, Philadelphia, Pennsylvania 19104-6316, USA *E-mail: [e-mail]. Search for other works by this author on: GSW Google Scholar Theodore A. Brzinski, III Theodore A. Brzinski, III 2Department of Physics and Astronomy, University of Pennsylvania, 209 S. 33rd Street, Philadelphia, Pennsylvania 19104-6396, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Douglas J. Jerolmack * 1Department of Earth and Environmental Science, University of Pennsylvania, 240 S. 33rd Street, Philadelphia, Pennsylvania 19104-6316, USA Theodore A. Brzinski, III 2Department of Physics and Astronomy, University of Pennsylvania, 209 S. 33rd Street, Philadelphia, Pennsylvania 19104-6396, USA *E-mail: [e-mail]. Publisher: Geological Society of America Received: 01 Dec 2009 Revision Received: 04 Mar 2010 Accepted: 08 Mar 2010 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2010 Geological Society of America Geology (2010) 38 (8): 719–722. https://doi.org/10.1130/G30922.1 Article history Received: 01 Dec 2009 Revision Received: 04 Mar 2010 Accepted: 08 Mar 2010 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Douglas J. Jerolmack, Theodore A. Brzinski; Equivalence of abrupt grain-size transitions in alluvial rivers and eolian sand seas: A hypothesis. Geology 2010;; 38 (8): 719–722. doi: https://doi.org/10.1130/G30922.1 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 Gravel-bed rivers organize to a threshold state in which the fluid stress during dominant flow conditions slightly exceeds the critical value. These channels change fairly abruptly to sand-dominated beds, facilitated by a paucity of sediment in the range of 1–10 mm. Eolian sediments are also bimodal; sand seas often transition rapidly downwind to silty loess deposits. In this paper we hypothesize that both transitions result from the same processes: (1) production of fine sediment by spallation from saltation abrasion of coarse grains, and (2) segregation of fine and coarse modes by suspension and saltation transport, respectively. We demonstrate that gravel rivers and eolian dune fields are dynamically equivalent in terms of threshold transport (Shields stress) and collision dynamics (Stokes number). While abrasion may not be the dominant cause of downstream fining of fluvial gravels, the reduction of collision efficiency with grain diameter sets a lower limit on gravel size, leading to a grain-size gap. The collision efficiency hypothesis potentially reconciles conflicting studies on the importance of sorting and lithology in downstream fining. Shields and Stokes similitude in rivers and deserts may be used to design appropriately scaled experiments to test and refine our hypothesis. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.