The dynamics and thermodynamics of large ash flows

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doi: 10.1007/s004450050134
Authors:Bursik, M. I.; Woods, A. W.
Author Affiliations:Primary:
State Univ. New York, Dept. Geol., Buffalo, NY, United States
Volume Title:Bulletin of Volcanology
Source:for the [Bulletin of Volcanology, 58(2-3), p.175-193. Publisher: Springer International] International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI), Heidelberg, International. ISSN: 0258-8900
Publication Date:1996
Note:In English. 81 refs.; 1 table, sects.
Summary:Ash flow deposits of up to 1000 km3 of material have been produced by some of the largest volcanic eruptions known. Ash flows propagate several 10 km from their source vents, produce extensive blankets of ash and are able to surmount topographic barriers some 102 m high. A new model of the motion of such flows predicts that for a given eruption rate, either a slow and deep subcritical flow or a fast and shallow supercritical flow may develop. The former propagate with a nearly constant volume flux, while the latter entrain air and become progressively more voluminous. The run-out distance of such flows is controlled largely by the mass of air mixed into the collapsing fountain, the degree of fragmentation and the associated rate of loss of material into an underlying concentrated depositional system, and the mass eruption rate. However, in supercritical flows, the continued entrainment of air exerts a further important control on the flow evolution. The model is consistent with observations of pyroclastic flow deposits, including the 1912 eruption of Katmai and the 1991 eruption of Pinatubo. It suggests that many extensive flow sheets were emplaced from eruptions with mass fluxes of 109-1010 kg/s over periods of 103-105 s, and that some indicators of flow 'mobility' may need to be reinterpreted. Furthermore, in accordance with observations, the model predicts that the coignimbrite eruption columns produced from such ash flows should rise 20-40 km. [R.E.S.]
Subjects:Ash flows; Dynamics; Gases; Grain size; Mathematical models; Morphology; Spatial distribution; Temperature; Thermodynamic properties; Velocity; Volcanic ash
Abstract Numbers:97M/3200
Record ID:1998027638
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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