Genesis of glacial flutes inferred from observations at Múlajökull, Iceland

Research Article| March 06, 2019 Genesis of glacial flutes inferred from observations at Múlajökull, Iceland L.R.W. Ives; L.R.W. Ives 1Department of Geological and Atmospheric Sciences, Iowa State University, Ames, Iowa 50011-3212, USA Search for other works by this author on: GSW Google Scholar N.R. Iverson N.R. Iverson 1Department of Geological and Atmospheric Sciences, Iowa State University, Ames, Iowa 50011-3212, USA Search for other works by this author on: GSW Google Scholar Author and Article Information L.R.W. Ives 1Department of Geological and Atmospheric Sciences, Iowa State University, Ames, Iowa 50011-3212, USA N.R. Iverson 1Department of Geological and Atmospheric Sciences, Iowa State University, Ames, Iowa 50011-3212, USA Publisher: Geological Society of America Received: 16 Oct 2018 Revision Received: 10 Jan 2019 Accepted: 10 Feb 2019 First Online: 06 Mar 2019 Online Issn: 1943-2682 Print Issn: 0091-7613 © 2019 Geological Society of America Geology (2019) 47 (5): 387–390. https://doi.org/10.1130/G45714.1 Article history Received: 16 Oct 2018 Revision Received: 10 Jan 2019 Accepted: 10 Feb 2019 First Online: 06 Mar 2019 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation L.R.W. Ives, N.R. Iverson; Genesis of glacial flutes inferred from observations at Múlajökull, Iceland. Geology 2019;; 47 (5): 387–390. doi: https://doi.org/10.1130/G45714.1 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 Flutes are flow-parallel till ridges that form subglacially and are conspicuous geomorphic indicators of slip at glacier beds. Flutes commonly have a boulder at their head, lodged in the former till bed of the glacier. In the leading model of flute genesis, weak till of the bed flows into a water-filled cavity where ice separates from the lee surface of the boulder. This cavity is displaced downstream as it progressively fills with till and the flute lengthens. To test this hypothesis, we studied in detail a parallel-sided flute, 250 m long, and a tapered flute, 5 m long, at the surge-type glacier, Múlajökull, in Iceland. More than 900 measurements of till magnetic susceptibility anisotropy, calibrated experimentally, show that spatially averaged till flow converged toward flute long axes, consistent with the cavity-fill hypothesis, and that till shear strains were small (<7.6). Till density patterns indicate that decreasing water pressure in cavities, decreasing slip velocity, and associated increases in ice pressure on the distal ends of the flutes consolidated and strengthened till—an effect far more prominent in the long flute. This till strengthening resolves the fundamental mechanical problem that undermines the cavity-fill hypothesis: how a leeward cavity can be sustained well beyond the pressure shadow in ice created by a boulder. Also resolved is how convergent fabrics in flutes are preserved, despite significant slip of ice across them. These results provide the first evidence that flute elongation beneath wet-based glaciers may require fluctuating water pressure and slip velocity. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.