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Published June 2010 | Supplemental Material + Published
Journal Article Open

Unsteady high-pressure flow experiments with applications to explosive volcanic eruptions


Motivated by the hypothesis that volcanic blasts can have supersonic regions, we investigate the role of unsteady flow in jets from a high-pressure finite reservoir. We examine the processes for formation of far-field features, such as Mach disk shocks, by using a shock tube facility and numerical experiments to investigate phenomena to previously unobtained pressure ratios of 250:1. The Mach disk shock initially forms at the edges of the vent and moves toward the centerline. The shock is established within a few vent diameters and propagates downstream toward the equilibrium location as the jet develops. The start-up process is characterized by two different timescales: the duration of supersonic flow at the nozzle exit and the formation time of the Mach disk shock. The termination process also is characterized by two different timescales: the travel time required for the Mach disk shock to reach its equilibrium position and the time at which the Mach disk shock begins significantly to collapse away from its equilibrium position. The critical comparisons for the formation of steady state supersonic regions are between the two start-up timescales and the termination timescales. We conclude that for typical vulcanian eruptions and the Mount St. Helens directed blast, the Mach disk shock could have formed near the vent, and that there was time for it to propagate a distance comparable to its equilibrium location. These experiments provide a framework for analysis of short-lived volcanic eruptions and data for benchmarking simulations of jet structures in explosive volcanic blasts.

Additional Information

© 2010 by the American Geophysical Union. Received 17 September 2009; revised 23 December 2009; accepted 14 January 2010; published 23 June 2010. NSF grant EAR06‐09712, NSF grant SK2008‐0035 8 ANTC and Charles R. Walgreen Jr. endowed funds to Susan W. Kieffer. We are grateful to James Quirk for the use of his code Amrita. We thank David Buchta at UIUC for performing modeling runs with a different code to cross‐check our results.

Attached Files

Published - jgrb16403.pdf

Supplemental Material - jgrb16403-sup-0001-t01.txt

Supplemental Material - jgrb16403-sup-0002-t02.txt

Supplemental Material - jgrb16403-sup-0003-t03.txt


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August 22, 2023
October 17, 2023