Mount St. Helens 1980 and Mount Pelee 1902—Flow or surge?

Research Article| October 01, 1983 Mount St. Helens 1980 and Mount Pelee 1902—Flow or surge? George P. L. Walker; George P. L. Walker 1Hawaii Institute of Geophysics, 2525 Correa Road, Honolulu, Hawaii 96822 Search for other works by this author on: GSW Google Scholar Lisa A. McBroome Lisa A. McBroome 1Hawaii Institute of Geophysics, 2525 Correa Road, Honolulu, Hawaii 96822 Search for other works by this author on: GSW Google Scholar Geology (1983) 11 (10): 571–574. https://doi.org/10.1130/0091-7613(1983)11<571:MSHAMP>2.0.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 George P. L. Walker, Lisa A. McBroome; Mount St. Helens 1980 and Mount Pelee 1902—Flow or surge?. Geology 1983;; 11 (10): 571–574. doi: https://doi.org/10.1130/0091-7613(1983)11<571:MSHAMP>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 SocietyGeology Search Advanced Search Abstract The far-reaching directed "blast" of Mount St. Helens and the devastating nuees ardentes of Mount Pelée produced deposits that in many places consist of three main layers: a basal gravelly or sandy layer 1, a massive or bedded ash layer 2, and a capping ash-cloud layer 3. These thin and in part landscape-mantling deposits are generally ascribed to pyroclastic surges, and the dune bedding seen in parts of layer 2 has reinforced this interpretation. There are several reasons, however, for preferring a pyroclastic-flow origin: (1) much of layer 2 is unequivocal pyroclastic flow; (2) the tripartite subdivision and landscape mantling habit is similar to that displayed by ignimbrites of the low-aspect-ratio type; (3) the deflation of a pyroclastic surge and the subsequent deposition of particulate material will tend not to conserve the fine ash and dust that are abundant in valley-ponded parts of layer 2 and cannot explain the observed tendency for layer 2 to show stronger fines depletion on ridges than in valley bottoms; and (4) the coarseness and the variance of grain size found within dune-bedded bed sets in Mount St. Helens layer 2 are like those of very weak pyroclastic surges, and the dune bedding most likely resulted from local minor turbulence (as could have been caused by surface roughness in a mountainous terrain littered with tree stumps and fallen trees) in a thin depositing pyroclastic flow. The directed blast and nuees ardentes at Mount St. Helens and Mount Pelée are interpreted to have been violently emplaced pyroclastic flows producing deposits of low-aspect-ratio type, the characteristics of which stem from an exceptionally high flow velocity. 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.