Subaqueous Pyroclastic Flows in the Ohanapecosh Formation, Washington

Abstract

Research Article| April 01, 1963 Subaqueous Pyroclastic Flows in the Ohanapecosh Formation, Washington RICHARD S FISKE RICHARD S FISKE Dept. Geology, The Johns Hopkins University, Baltimore, Md Search for other works by this author on: GSW Google Scholar Author and Article Information RICHARD S FISKE Dept. Geology, The Johns Hopkins University, Baltimore, Md Publisher: Geological Society of America Received: 18 Sep 1961 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1963, 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 (1963) 74 (4): 391–406. https://doi.org/10.1130/0016-7606(1963)74[391:SPFITO]2.0.CO;2 Article history Received: 18 Sep 1961 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation RICHARD S FISKE; Subaqueous Pyroclastic Flows in the Ohanapecosh Formation, Washington. GSA Bulletin 1963;; 74 (4): 391–406. doi: https://doi.org/10.1130/0016-7606(1963)74[391:SPFITO]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 Subaqueous pyroclastic flows form almost one-half of the 10,000-foot Ohanapecosh Formation (Eocene and Oligocene?) in the eastern part of Mount Rainier National Park, Washington. Most of these flows probably originated by the sloughing of debris from the flanks of active underwater volcanoes during and after pyroclastic eruptions. Some of the pyroclastic flows caused directly by underwater eruptions may not have been completely quenched and could have traveled as steam-inflated slurries of pyroclastic debris and water. Most of them, however, were probably cold or only slightly warm as they flowed into deeper water.The Ohanapecosh subaqueous pyroclastic flows are extensive, nonwelded deposits of lapilli-tuff or fine tuff-breccia ranging in thickness from 10 to more than 200 feet. They are interbedded with thinner and generally finer turbidity-current and ash-fall deposits formed by smaller and more water-rich slumps of pyroclastic debris from the underwater volcanoes and by ash falls that rained into the water.The three main types of flows are thought to be related to three different kinds of volcanic activity. The most common flows—those containing a variety of lithic fragments and variable amounts of pumice—were probably produced by underwater phreatic eruptions. The flows rich in pumice and glass shards were probably caused by underwater eruptions of rapidly vesiculating magma which, on land, would have produced hot ash flows or ash falls. The least common flows—those containing only one or two kinds of lithic fragments—were probably derived from fairly homogeneous bodies, such as domes, spines, and lava flows that were erupted into water and fragmented by steam-blast explosions.Remnants of the underwater Ohanapecosh volcanoes consist chiefly of coarse tuff-breccia piled around filled volcanic vents. Unbrecciated lava flows are subordinate and were probably deposited on land when the volcanoes succeeded in growing into islands. 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.