Rates and processes of bedrock incision by the Upper Ukak River since the 1912 Novarupta ash flow in the Valley of Ten Thousand Smokes, Alaska

Research Article| September 01, 2000 Rates and processes of bedrock incision by the Upper Ukak River since the 1912 Novarupta ash flow in the Valley of Ten Thousand Smokes, Alaska Kelin X. Whipple; Kelin X. Whipple 1Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Search for other works by this author on: GSW Google Scholar Noah P. Snyder; Noah P. Snyder 1Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Search for other works by this author on: GSW Google Scholar Kate Dollenmayer Kate Dollenmayer 1Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Kelin X. Whipple 1Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Noah P. Snyder 1Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Kate Dollenmayer 1Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Publisher: Geological Society of America Received: 14 Jan 2000 Revision Received: 19 Jun 2000 Accepted: 30 Jun 2000 First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2000) 28 (9): 835–838. https://doi.org/10.1130/0091-7613(2000)282.0.CO;2 Article history Received: 14 Jan 2000 Revision Received: 19 Jun 2000 Accepted: 30 Jun 2000 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Kelin X. Whipple, Noah P. Snyder, Kate Dollenmayer; Rates and processes of bedrock incision by the Upper Ukak River since the 1912 Novarupta ash flow in the Valley of Ten Thousand Smokes, Alaska. Geology 2000;; 28 (9): 835–838. doi: https://doi.org/10.1130/0091-7613(2000)282.0.CO;2 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 The rates and patterns of bedrock channel incision significantly influence landscape evolution and long-term interactions among climate, tectonics, and erosion. Unfortunately, only sparse field data are available to quantify the controls on river incision rates. We exploit the diversion of the upper Ukak River by an ash flow in 1912 to measure rates of incision along a newly formed bedrock channel. Minimum estimates of the rate of incision into intact rock vary from 0.01 to 0.10 m ṁ yr−1. This variation reflects differences in channel slope, channel width, lithologic facies, and intensity of jointing as well as the effects of upstream knickpoint migration. A stream-power–type incision model adequately explains the incision-rate data, provided (1) variations in channel width are prescribed on the basis of field measurements, (2) the slope exponent is significantly less than unity (n = 0.4 ± 0.2), and (3) observed downstream changes in lithologic facies and the intensity of jointing account for the apparent twofold downstream decrease in the coefficient of erosion. Despite the very rapid rate of incision, calibrated stream-power erosion coefficients for the Ukak River (K = 2.4 × 10−4 m0.2 ṁ yr−1 to 9.0 × 10−4 m0.2 ṁ yr−1) are within the range of previously published estimates. Two plausible explanations for the low values of the slope exponent n are that incision rate is limited by either (1) a combination of physical weathering and hydrodynamic joint-block extraction or (2) block fracture due to bedload impacts modulated on steeper channel segments by suspension of a significant fraction of the sediment load. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.