Lava Tubes of the Cave Basalt, Mount St. Helens, Washington

Abstract

Research Article| August 01, 1972 Lava Tubes of the Cave Basalt, Mount St. Helens, Washington RONALD GREELEY; RONALD GREELEY Space Science Division, Ames Research Center, National Aeronautics and Space Administration, Moffet Field, California 94035 Search for other works by this author on: GSW Google Scholar JACK H HYDE JACK H HYDE U.S. Geological Survey and Tacoma Community College, Tacoma, Washington 98465 Search for other works by this author on: GSW Google Scholar Author and Article Information RONALD GREELEY Space Science Division, Ames Research Center, National Aeronautics and Space Administration, Moffet Field, California 94035 JACK H HYDE U.S. Geological Survey and Tacoma Community College, Tacoma, Washington 98465 Publisher: Geological Society of America Received: 26 Aug 1971 Revision Received: 09 Mar 1972 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1972, 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 (1972) 83 (8): 2397–2418. https://doi.org/10.1130/0016-7606(1972)83[2397:LTOTCB]2.0.CO;2 Article history Received: 26 Aug 1971 Revision Received: 09 Mar 1972 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation RONALD GREELEY, JACK H HYDE; Lava Tubes of the Cave Basalt, Mount St. Helens, Washington. GSA Bulletin 1972;; 83 (8): 2397–2418. doi: https://doi.org/10.1130/0016-7606(1972)83[2397:LTOTCB]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 Cave Basalt, a high-alumina pahoehoe flow containing numerous lava tubes, originated at the southeast flank of Mount St. Helens, southwestern Washington, and flowed down a stream valley incised in older pyroclastic flow deposits. In situ charcoal samples from two localities within lava tubes yield C14 dates of 1,860 ± 250 years B.P. and 1,925 ± 95 years B.P. Detailed survey of 9,125 m of lava tubes, correlated with surface geologic mapping, yields several geomorphic relations of basalt flows. Most of the lava tubes apparently formed between shear planes in laminar lava flow, although some tube sections show evidence that the tube roof formed by accretion of spattered lava in turbulent flow. Partial collapse of tube interiors reveals: (1) The wall separating the tube interior from the preflow country rock may be thinner than 25 cm. (2) Lava flows can erode the surface over which they flow. (3) Collapse of the tube interior can occur immediately after the tube has been drained of molten lava and before the walls cool completely. (4) Lava tubes may represent the thickest part of the lava flow, occupying topographic lows (stream channels). (5) Tubes can be modified extensively through accretion and erosion by later lava flows.Many surface features of basalt flows are directly related to lava tubes. Pressure within the closed lava-tube system caused by out-gassing and hydrostatic pressure and overflow of lava from ruptured roof sections (or from channel overflow prior to roof formation) result in formation of a topographic high along many sections of the lava-tube axis. If roof rupture does not occur, tumuli may develop in weak areas of the roof, forming positive features (may be solid or hollow) 40 to 50 m in diameter and several meters high. Most of the hollow tumuli of the Cave Basalt collapsed, probably as a result of withdrawal of supporting lava during drainage of the lava tubes. Raised-rim craters found in many parts of the flow are associated with lava tubes and were probably formed by collapse of hollow tumuli. 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.