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Published April 2014 | Published
Journal Article Open

Flow of supersonic jets across flat plates: Implications for ground-level flow from volcanic blasts


We report on laboratory experiments examining the interaction of a jet from an overpressurized reservoir with a canonical ground surface to simulate lateral blasts at volcanoes such as the 1980 blast at Mount St. Helens. These benchmark experiments test the application of supersonic jet models to simulate the flow of volcanic jets over a lateral topography. The internal shock structure of the free jet is modified such that the Mach disk shock is elevated above the surface. In elevation view, the width of the shock is reduced in comparison with a free jet, while in map view the dimensions are comparable. The distance of the Mach disk shock from the vent is in good agreement with free jet data and can be predicted with existing theory. The internal shock structures can interact with and penetrate the boundary layer. In the shock-boundary layer interaction, an oblique shock foot is present in the schlieren images and a distinctive ground signature is evident in surface measurements. The location of the oblique shock foot and the surface demarcation are closely correlated with the Mach disk shock location during reservoir depletion, and therefore, estimates of a ground signature in a zone devastated by a blast can be based on the calculated shock location from free jet theory. These experiments, combined with scaling arguments, suggest that the imprint of the Mach disk shock on the ground should be within the range of 4–9 km at Mount St. Helens depending on assumed reservoir pressure and vent dimensions.

Additional Information

© 2014 American Geophysical Union. Received 2 OCT 2013; Accepted 1 APR 2014; Accepted article online 3 APR 2014; Published online 24 APR 2014. This work was supported in part by NSF grant EAR06-09712, NSF grant SK2008-0035 8, and NASA grant NNX08AN10G. S.W.K. thanks the Charles R. Walgreen Jr. Foundation for support. The authors gratefully acknowledge Matthew Leibowitz and Miquela Trujillo at the University of Illinois for their contributions to the experimental data.

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