TY - JOUR
T1 - Ice thickness and topographic relief in glaciated landscapes of the western USA
AU - Brocklehurst, Simon H.
AU - Whipple, Kelin
AU - Foster, David
N1 - Funding Information:
This work was supported by a NASA GSFC Graduate Student Research Grant, NSF grant EAR-9980465 (to KXW), a GSA Fahnestock Award, a NASA Graduate Fellowship, a CIRES Visiting Fellowship, and Nuffield Foundation Award NAL/00941/G (all to SHB). We would like to thank Ryan Ewing and Noah Snyder for assistance in the field, Ben Crosby and Darryl Granger for detailed comments on early drafts of this manuscript, and Peter van der Beek and Ola Fredin, for thorough and constructive reviews.
PY - 2008/5/1
Y1 - 2008/5/1
N2 - The development of relief in glaciated landscapes plays a crucial role in hypotheses relating climate change and tectonic processes. In particular, glaciers can only be responsible for peak uplift if they are capable of generating significant relief in formerly nonglaciated landscapes. Previous work has suggested that relief in glaciated landscapes should scale with the thickness of the ice. Here we summarise a field-based test of this hypothesis in two mountain ranges in the western United States, the Sierra Nevada, California, and the Sangre de Cristo Range, Colorado. These areas exhibit a range of degrees of glacial occupation during the Quaternary, including some drainage basins essentially unoccupied by ice, allowing a detailed exploration of how relief in different parts of a drainage basin evolves in response to glacial modification. We mapped last glacial maximum (LGM) trimlines to estimate the ice thickness at the equilibrium line altitude during the LGM, and determined several metrics of relief for drainage basins across the full spectrum of LGM ice extents. Comparison between measures of relief and ice thickness estimates indicates that relief production in glaciated mountain belts scales with ice thickness and consequently also drainage area. We extended our study to the Bitterroot Range in Idaho/Montana, and the Teton Range in Wyoming, for a more comprehensive understanding of sub-ridgeline relief, or 'missing mass'. This measure of mean relief is surprisingly little affected by either the degree of glacial modification or the total material removed by glaciers, but appears to be influenced by the more active tectonics of the Teton Range. While the effects of glacial modification on the landscape are clear (valley widening, hanging valley formation), the overall change in the relief structure of the mountain ranges studied here is surprisingly modest.
AB - The development of relief in glaciated landscapes plays a crucial role in hypotheses relating climate change and tectonic processes. In particular, glaciers can only be responsible for peak uplift if they are capable of generating significant relief in formerly nonglaciated landscapes. Previous work has suggested that relief in glaciated landscapes should scale with the thickness of the ice. Here we summarise a field-based test of this hypothesis in two mountain ranges in the western United States, the Sierra Nevada, California, and the Sangre de Cristo Range, Colorado. These areas exhibit a range of degrees of glacial occupation during the Quaternary, including some drainage basins essentially unoccupied by ice, allowing a detailed exploration of how relief in different parts of a drainage basin evolves in response to glacial modification. We mapped last glacial maximum (LGM) trimlines to estimate the ice thickness at the equilibrium line altitude during the LGM, and determined several metrics of relief for drainage basins across the full spectrum of LGM ice extents. Comparison between measures of relief and ice thickness estimates indicates that relief production in glaciated mountain belts scales with ice thickness and consequently also drainage area. We extended our study to the Bitterroot Range in Idaho/Montana, and the Teton Range in Wyoming, for a more comprehensive understanding of sub-ridgeline relief, or 'missing mass'. This measure of mean relief is surprisingly little affected by either the degree of glacial modification or the total material removed by glaciers, but appears to be influenced by the more active tectonics of the Teton Range. While the effects of glacial modification on the landscape are clear (valley widening, hanging valley formation), the overall change in the relief structure of the mountain ranges studied here is surprisingly modest.
KW - Glacial geomorphology
KW - Landscape evolution
KW - Relief
UR - http://www.scopus.com/inward/record.url?scp=41649109226&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=41649109226&partnerID=8YFLogxK
U2 - 10.1016/j.geomorph.2007.02.037
DO - 10.1016/j.geomorph.2007.02.037
M3 - Article
AN - SCOPUS:41649109226
SN - 0169-555X
VL - 97
SP - 35
EP - 51
JO - Geomorphology
JF - Geomorphology
IS - 1-2
ER -