Dynamics of co-ignimbrite plumes generated from pyroclastic flows of Mount St. Helens (7 August 1980)

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doi: 10.1007/s004450050151
Authors:Calder, E. S.; Sparks, R. S. J.; Woods, A. W.
Author Affiliations:Primary:
Univ. Bristol, Dept. Geol., Bristol, United Kingdom
Volume Title:Bulletin of Volcanology
Source:for the [Bulletin of Volcanology, 58(6), p.432-440. Publisher: Springer International] International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI), Heidelberg, International. ISSN: 0258-8900
Publication Date:1997
Note:In English. 15 refs.; illus.
Summary:Plume generation may be triggered by enhanced mixing due to a hydrualic jump associated with abrupt change of slope. Generation in discrete pulses of three of the day's four co-ignimbrite plumes was linked to changes in channel slope; that of the fourth was at the channel mouth where the flow decelerated on meeting the pumice plain. Measurements show that from initial velocities of 1-2 m/s two plumes reached maxima of 4.6 and 8.8 m/s respectively at heights of 270 and 315 m above the flow before decelerating. The others reached velocities of 6.2 and 13 m/s. All four plumes became less energetic downstream as a consequence of decreasing interaction between the pyroclastic flow front and the atmosphere. Theoretical models agree well with observations and suggest initial ascent in terms of a discrete thermal cloud expanding as it entrains air, whereas subsequent motion of the head is influenced by material from the following plume. Models and observations agree on an initial T of 500-600 K for the air and ash mixture - consistent with the measured initial ash T of 920 K. Ash masses of 3.4 × 105 to 1.8 × 106 kg are estimated. [E.H.F.]
Subjects:Cenozoic; Dynamics; Holocene; Igneous rocks; Ignimbrite; Mantle; Mantle plumes; Models; Pyroclastic flows; Pyroclastics; Quaternary; Slopes; Topography; Upper Holocene; Volcanic rocks; Volcanoes; Cascade Range; Mount Saint Helens; Skamania County Washington; United States; Washington
Coordinates:N461200 N461200 W1221100 W1221100
Abstract Numbers:97M/4406
Record ID:2000050208
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
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