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Volume 6, issue 3 | Copyright
Earth Surf. Dynam., 6, 595-610, 2018
https://doi.org/10.5194/esurf-6-595-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 26 Jul 2018

Research article | 26 Jul 2018

Tectonic controls of Holocene erosion in a glaciated orogen

Byron A. Adams1,a and Todd A. Ehlers1 Byron A. Adams and Todd A. Ehlers
  • 1Department of Geosciences, Universität Tübingen, 72074, Germany
  • anow at: the School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, UK

Abstract. Recent work has highlighted a strong, worldwide, alpine glacial impact on orogen erosion rates over the last 2Ma. While it may be assumed that glaciers increased erosion rates when active, the degree to which past glaciations influence Holocene erosion rates through the adjustment of topography is not known. In this study, we investigate the influence of long-term tectonic and post-glacial topographic controls on erosion in a glaciated orogen: the Olympic Mountains, USA. We present 14 new 10Be and 26Al analyses which constrain Holocene erosion rates across the Olympic Mountains. Basin-averaged erosion rates scale with basin-averaged values of 5km local relief, channel steepness, and hillslope angle throughout the range, similar to observations from non-glaciated orogens. These erosion rates are not related to mean annual precipitation or the marked change in Pleistocene alpine glacier size across the range, implying that glacier modification of topography and modern precipitation parameters do not exert strong controls on these rates. Rather, we find that despite spatial variations in glacial modification of topography, patterns of recent erosion are similar to those from estimates of long-term tectonic rock uplift. This is consistent with a tectonic model where erosion and rock uplift patterns are controlled by the deformation of the Cascadia subduction zone.

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Where alpine glaciers were active in the past, they have created scenic landscapes that are likely in the process of morphing back into a form that it more stable with today's climate regime and tectonic forces. By looking at older erosion rates from before the time of large alpine glaciers and erosion rates since deglaciation in the Olympic Mountains (USA), we find that the topography and erosion rates have not drastically changed despite the impressive glacial valleys that have been carved.
Where alpine glaciers were active in the past, they have created scenic landscapes that are...
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