Eruption of Lassen Peak, Cascade Range, California, in 1915: Example of Mixed Magmas

Abstract

Research Article| May 01, 1965 Eruption of Lassen Peak, Cascade Range, California, in 1915: Example of Mixed Magmas GORDON A MACDONALD; GORDON A MACDONALD Institute of Geophysics, University of Hawaii, Honolulu, Hawaii Search for other works by this author on: GSW Google Scholar TAKASHI KATSURA TAKASHI KATSURA Tokyo Institute of Technology, Tokyo, Japan Search for other works by this author on: GSW Google Scholar Author and Article Information GORDON A MACDONALD Institute of Geophysics, University of Hawaii, Honolulu, Hawaii TAKASHI KATSURA Tokyo Institute of Technology, Tokyo, Japan Publisher: Geological Society of America Received: 19 Jun 1964 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1965, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1965) 76 (5): 475–482. https://doi.org/10.1130/0016-7606(1965)76[475:EOLPCR]2.0.CO;2 Article history Received: 19 Jun 1964 First Online: 02 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 GORDON A MACDONALD, TAKASHI KATSURA; Eruption of Lassen Peak, Cascade Range, California, in 1915: Example of Mixed Magmas. GSA Bulletin 1965;; 76 (5): 475–482. doi: https://doi.org/10.1130/0016-7606(1965)76[475:EOLPCR]2.0.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 SocietyGSA Bulletin Search Advanced Search Abstract The pumice of the 1915 eruption of Lassen Peak is conspicuously banded. Light bands are dacite; dark bands are andesite. They represent two distinct magmas which were imperfectly mixed at the time of eruption; the portions of different composition were drawn out into bands by flowage. Similar, but less obvious and possibly less extreme, inhomogeneity exists in the lava flow of the same eruption. In both lava flow and pumice, the phenocrysts were out of equilibrium with the enclosing magma and were reacting with it. Numerous feldspar phenocrysts that originated in the dacite portion show clouding, which resulted from fritting of their outer parts, and a more calcic outer zone; however this appears to be related only in small part to the addition of the basic magma, represented by the dark streaks in the pumice. These feldspars probably are remnants of remelted granitic rocks of the underlying sialic basement admixed with basaltic magma rising from still greater depth. Phreatic explosions in 1914 probably resulted from distension of the Lassen dome by the rise of new magma. 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.