Interrelations among pyroclastic surge, pyroclastic flow, and lahars in Smith Creek valley during first minutes of 18 May 1980 eruption of Mount St. Helens, USA

Saved in:
Authors:Brantley, S. R.; Waitt, R. B.
Author Affiliations:Primary:
U. S. Geol. Surv., Cascades Volcano Obs., Vancouver, WA 98661, United States
Volume Title:Bulletin of Volcanology
Source:for the [Bulletin of Volcanology, 50(5), p.304-326. Publisher: Springer International] International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI), Heidelberg, International. ISSN: 0258-8900
Publication Date:1988
Note:In English. 51 refs.; illus. incl. geol. sketch map, sects.
Summary:A devastating pyroclastic surge and resultant lahars at Mt St Helens produced several catastrophic flowages into tributaries on the NE flank of the volcano. The lahars must have originated as snowmelt, not as ejected water-saturated debris that segregated from the pyroclastic surge as has been inferred for other flanks of the volcano. In stratigraphic order the Smith Creek valley-floor materials comprise: 1) a complex valley-bottom facies of the pyroclastic surge and a related pyroclastic flow; 2) an unusual hummocky diamict caused by complex mixing of lahars with the dry pyroclastic debris; and 3) deposits of secondary pyroclastic flows. These units are capped by silt containing accretionary lapilli, which began falling from a rapidly expanding cloud 20 min. after the eruption's onset. The unusual hummocky diamict (< or equal to 15 m thick) contains large lithic clasts supported by a brown muddy sand matrix and is the result of a high-viscosity debris flow which formed when lahars mingled with the pyroclastic material on Smith Creek valley floor. [R.A.H.]
Subjects:Cenozoic; Distribution; Eruptions; Holocene; Igneous rocks; Mass movements; Mudflows; Pyroclastics; Quaternary; Stratigraphic units; Volcanic rocks; Volcanoes; Volcanology; Cascade Range; Mount Saint Helens; Skamania County Washington; United States; Washington; Smith Creek Valley
Abstract Numbers:89M/2464
Record ID:1989059071
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom, Reference includes data from Geoline, Bundesanstalt fur Geowissenschaften und Rohstoffe
Tags: Add Tag
No Tags, Be the first to tag this record!
Be the first to leave a comment!
You must be logged in first