Valley asymmetry and glacial versus nonglacial erosion in the Bitterroot Range, Montana, USA

Research Article| April 01, 2007 Valley asymmetry and glacial versus nonglacial erosion in the Bitterroot Range, Montana, USA Shawn Naylor; Shawn Naylor 1Department of Geosciences, University of Montana, Missoula, Montana 59812, USA Search for other works by this author on: GSW Google Scholar Emmanuel J. Gabet Emmanuel J. Gabet 2Department of Environmental Sciences, University of California–Riverside, Riverside, California 92521, USA Search for other works by this author on: GSW Google Scholar Geology (2007) 35 (4): 375–378. https://doi.org/10.1130/G23283A.1 Article history received: 20 Sep 2006 rev-recd: 06 Dec 2006 accepted: 11 Dec 2006 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 Shawn Naylor, Emmanuel J. Gabet; Valley asymmetry and glacial versus nonglacial erosion in the Bitterroot Range, Montana, USA. Geology 2007;; 35 (4): 375–378. doi: https://doi.org/10.1130/G23283A.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 Theories that propose feedbacks among climate, tectonics, and surface processes commonly assume that erosion is enhanced by glacial activity. Indeed, studies have shown that glaciers appear to limit the elevation of mountain ranges; however, comparisons between rates of glacial and nonglacial erosion are difficult to make. Ideally, such comparisons must hold precipitation and lithology constant, while only varying the erosional regime. Located in a climatic transition zone during the Pleistocene, the east-west–trending valleys of the Bitterroot Range present an opportunity for a quantitative analysis of glacial and nonglacial erosion because the north-facing sides of the valleys were glaciated, whereas the south-facing slopes were not. The different erosional regimes operating on either side of the valleys created strongly asymmetric ridges. Ridgelines separating the east-west–trending valleys have been pushed southward by glacial headwall retreat such that ridge-to-valley distances are ∼50% greater on the north-facing slopes than on the south-facing slopes. In addition, mean hillslope angles are 6° lower on the glaciated slopes than on the unglaciated slopes, and calculations of geophysical relief suggest that, on average, glaciers have removed nearly twice as much rock as nonglacial processes. Finally, we conclude that, although rates of vertical incision by glacial processes in the Bitterroot Range were more rapid than nonglacial processes, the dominant geomorphological impact of glaciers was lateral erosion by headwall retreat. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.