Tree-ring dating of pre-1980 volcanic flowage deposits at Mount St. Helens, Washington

Abstract

Research Article| September 01, 1995 Tree-ring dating of pre-1980 volcanic flowage deposits at Mount St. Helens, Washington David K. Yamaguchi; David K. Yamaguchi 1Institute of Arctic and Alpine Research (INSTAAR), University of Colorado, Boulder, Colorado 80309 Search for other works by this author on: GSW Google Scholar Richard P. Hoblitt Richard P. Hoblitt 2U.S. Geological Survey, Cascades Volcano Observatory, 5400 MacArthur Boulevard, Vancouver, Washington 98661 Search for other works by this author on: GSW Google Scholar Author and Article Information David K. Yamaguchi 1Institute of Arctic and Alpine Research (INSTAAR), University of Colorado, Boulder, Colorado 80309 Richard P. Hoblitt 2U.S. Geological Survey, Cascades Volcano Observatory, 5400 MacArthur Boulevard, Vancouver, Washington 98661 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1995) 107 (9): 1077–1093. https://doi.org/10.1130/0016-7606(1995)107<1077:TRDOPV>2.3.CO;2 Article history First Online: 01 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 David K. Yamaguchi, Richard P. Hoblitt; Tree-ring dating of pre-1980 volcanic flowage deposits at Mount St. Helens, Washington. GSA Bulletin 1995;; 107 (9): 1077–1093. doi: https://doi.org/10.1130/0016-7606(1995)107<1077:TRDOPV>2.3.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 SocietyGSA Bulletin Search Advanced Search Abstract Tree-ring dating (ring-width pattern matching) was used to determine emplacement dates for eight subfossil-tree–bearing, pre-1980 pyroclastic-flow and lahar deposits in stream valleys draining Mount St. Helens, Washington. Limiting dates were also established for nine other pre-1980 flowage deposits from the ages of trees rooted on or near them, or from exhumed trees. The 17 new dates improve understanding of the chronology of events during and after Mount St. Helens's Kalama eruptive period, which extended from a.d. 1479 to the mid-1700s. We assign bracketing dates to the three phases of the Kalama eruptive period: 1479–1510 to the early Kalama, during which Mount St. Helens erupted explosive dacitic tephras, pyroclastic flows, and one or more domes; 1489–1566 to the middle Kalama, during which Mount St. Helens produced andesitic tephras, pyroclastic flows, and lava flows; and 1489–1750 to the late Kalama, during which Mount St. Helens again erupted dacite. Overlap of the brackets reflects the limits of our dating resolution. The revised chronology confirms that little time (perhaps 50 yr) elapsed between the end of Mount St. Helens's Kalama eruptive period and the start of the succeeding Goat Rocks eruptive period (a.d. 1800–1857). Eruptions apparently occurred sporadically during the entire 1479–1857 interval. The record also indicates that a large pyroclastic flow occurred 7–10 yr after the explosive eruptions that began the Kalama eruptive period. The dates further imply that extrusion of the pre-1980 summit dome continued intermittently for ≈ 100 yr and limit the ages of two tephras. These findings demonstrate the usefulness of relict tree-bearing deposits to volcanic history studies. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.