CaltechAUTHORS
  A Caltech Library Service

Dynamics of explosive degassing of magma: Observations of fragmenting two-phase flows

Mader, H. M. and Phillips, J. C. and Sparks, R. S. J. and Sturtevant, B. (1996) Dynamics of explosive degassing of magma: Observations of fragmenting two-phase flows. Journal of Geophysical Research. Solid Earth, 101 (B3). pp. 5547-5560. ISSN 2169-9313. http://resolver.caltech.edu/CaltechAUTHORS:20141028-160645725

[img]
Preview
PDF - Published Version
See Usage Policy.

1625Kb

Use this Persistent URL to link to this item: http://resolver.caltech.edu/CaltechAUTHORS:20141028-160645725

Abstract

Liquid explosions, generated by rapid degassing of strongly supersaturated liquids, have been investigated in the laboratory with a view to understanding the basic physical processes operating during bubble nucleation and growth and the subsequent behavior of the expanding two-phase flow. Experiments are carried out in a shock tube and are monitored by high-speed photography and pressure transducers. Theoretical CO_2 supersaturations up to 455 times the ambient saturation concentration are generated by a chemical reaction; K_2CO_3 solution is suddenly injected into an excess of HCl solution in such a way as to mix the two solutions rapidly. Immediately after the injection event, a bubble nucleation delay of a few milliseconds is followed by rapid nucleation and explosive expansion of CO_2 bubbles forming a highly heterogeneous foam. Enhanced diffusion due to advection in the flow coupled with continuous mixing of the reactants, and hence on-going bubble nucleation after injection, generates an increasingly accelerating flow until the reactants become depleted at peak accelerations of around 150 g and velocities of about 15 m s^(−1). Stretching of the accelerating two-phase mixture enhances the mixing. Liberation of CO_2 vapor is spatially inhomogeneous leading to ductile fragmentation occurring throughout the flow in regions of greatest gas release as the consequence of the collision and stretching of fluid streams. The violence of the eruptions is controlled by using different concentrations of the HCl and K_2CO_3 solutions, which alters the CO_2 supersaturation and yield and also the efficiency of the mixing process. Peak acceleration is proportional to theoretical supersaturation. Pressure measurements at the base of the shock tube show an initial nucleation delay and a pressure pulse related to the onset of explosive bubble formation. These chemically induced explosions differ from liquid explosions created in other experiments. In explosions caused by sudden depressurization of CO_2-saturated water, the bubbles nucleate uniformly throughout the liquid in a single nucleation event. Subsequent bubble growth causes the two-phase mixture to be accelerated upward at nearly constant accelerations. Explosively boiling liquids, in which heterogeneous nucleation is suppressed, experience an evaporation wave which propagates down into the liquid column at constant average velocity. Fragmentation occurs at the sharply defined leading edge of the wavefront. The chemical flows effectively simulate highly explosive volcanic eruptions as they are comparable in terms of flow densities, velocities, accelerations, and in the large range of scales present. The large accelerations cause strong extensional strain and longitudinal deformation. Comparable deformation rates in volcanic systems could be sufficient to approach conditions for brittle fragmentation. Tube pumice is a major component of plinian deposits and ignimbrites and preserves evidence of accelerating flow conditions.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1029/95JB02515DOIArticle
http://onlinelibrary.wiley.com/doi/10.1029/95JB02515/abstractPublisherArticle
Additional Information:Copyright 1996 by the American Geophysical Union. (Received September 23, 1994; revised July 31, 1995; accepted August 10, 1995.) Paper number 95JB02515. We would like to thank E. Stolper, Y. Zhang. K. V. Cashman and an anonymous reviewer for their helpful comments on the manuscript. This work and the salary of J. C. Phillips was funded by grant GR3/8620 from the Natural Environment Research Council, England, and by EC grant PL91049.
Funders:
Funding AgencyGrant Number
Natural Environment Research Council (NERC) GR3/8620
European Commission (EC)PL91049
Record Number:CaltechAUTHORS:20141028-160645725
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20141028-160645725
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:50965
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:28 Oct 2014 23:42
Last Modified:28 Oct 2014 23:42

Repository Staff Only: item control page