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Precursory Pressure Signals of Pyroclastic Density Currents

Anna Perttu 1, Gert Lube1, Art Jolly2, Eric C. P. Breard3, Ermanno Bosch1, Jeff Robert1

  • Affiliations: 1 Volcanic Risk Solutions, Massey University, Palmerston North, Aotearoa/New Zealand   2 Hawaiian Volcano Observatory, U.S. Geological Survey, Hilo, HI, USA 3 School of Geosciences, University of Edinburgh, Edinburgh, UK

  • Presentation type: Talk [Invited]

  • Presentation time: Friday 14:15 - 14:30, Room R380

  • Programme No: 3.9.1

  • Theme 3 > Session 9

Abstract

Pyroclastic Density Currents (PDCs) are complex gravity currents that are significant hazards during volcanic eruptions and are highly destructive to the natural and built environment, making them uniquely challenging for obtaining direct measurements. Thus, acoustics and seismo-acoustics have been investigated as a tool for interrogating PDCs in situ. We show through the use of large-scale analog experimental PDCs that these flows generate atmospheric pressure waves. We record and analyze two fundamentally different types of precursory pressure signals that precede the arrival of the flow. The first is an acoustic wave that is generated by the initiation of the PDC and the initial intrusion into the atmosphere like a dome collapse or column collapse. Additional pulses are generated by the underflow potentially leading to the ability to distinguish types of PDCs. This is consistent with early observation of pressure waves generated by dome collapse events at Unzen volcano in Japan. The second pressure signal is produced by drag by the front of the PDC in the ambient air. This significant increase of dynamic pressure immediately preceding the flow arrival is comparable with the dynamic pressure within the flow proper. Precursory pressure waves generated by PDCs should therefore be taken into account in hazard models for PDCs as we show that they have the potential to produce dynamic pressures on par with PDCs themselves. Identification and classification of precursory pressure signals from PDCs can lead to improved early warning systems and hazard mitigation.