Bulletin of Volcanology

, 76:855 | Cite as

Experimental study of dense pyroclastic density currents using sustained, gas-fluidized granular flows

  • Pete J. RowleyEmail author
  • Olivier Roche
  • Timothy H. Druitt
  • Ray Cas
Research Article


We present the results of laboratory experiments on the behaviour of sustained, dense granular flows in a horizontal flume, in which high-gas pore pressure was maintained throughout the flow duration by continuous injection of gas through the flume base. The flows were fed by a sustained (0.5–30 s) supply of fine (75 ± 15 μm) particles from a hopper; the falling particles impacted an impingement surface at concentrations of ~3 to 45 %, where they densified rapidly to generate horizontally moving, dense granular flows. When the gas supplied through the flume base was below the minimum fluidization velocity of the particles (i.e. aerated flow conditions), three flow phases were identified: (i) an initial dilute spray of particles travelling at 1–2 m s−1, followed by (ii) a dense granular flow travelling at 0.5–1 m s−1, then by (iii) sustained aggradation of the deposit by a prolonged succession of thin flow pulses. The maximum runout of the phase 2 flow was linearly dependent on the initial mass flux, and the frontal velocity had a square-root dependence on mass flux. The frontal propagation speed during phase 3 had a linear relationship with mass flux. The total mass of particles released had no significant control on either flow velocity or runout in any of the phases. High-frequency flow unsteadiness during phase 3 generated deposit architectures with progradational and retrogradational packages and multiple internal erosive contacts. When the gas supplied through the flume base was equal to the minimum fluidization velocity of the particles (i.e. fluidized flow conditions), the flows remained within phase 2 for their entire runout, no deposit formed and the particles ran off the end of the flume. Sustained granular flows differ significantly from instantaneous flows generated by lock-exchange mechanisms, in that the sustained flows generate (by prolonged progressive aggradation) deposits that are much thicker than the flowing layer of particles at any given moment. The experiments offer a first attempt to investigate the physics of the sustained pyroclastic flows that generate thick, voluminous ignimbrites.


Fluidization Pyroclastic flow Density current Pore pressure Sustained supply Experiments 



PR was supported by a Université Blaise Pascal postdoctoral fellowship, with experimental work funded by a grant from the volcanology group of the Laboratoire Magmas et Volcans. This is Laboratory of Excellence ClerVolc (ANR-10-LABX-0006) contribution number 106. We thank the reviewers B. Andrews and C. Wilson, whose comments and suggestions significantly improved this manuscript.

Supplementary material

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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Pete J. Rowley
    • 1
    • 2
    • 3
    Email author
  • Olivier Roche
    • 1
    • 2
    • 3
  • Timothy H. Druitt
    • 1
    • 2
    • 3
  • Ray Cas
    • 4
  1. 1.Clermont Université, Université Blaise Pascal, Laboratoire Magmas et VolcansClermont-FerrandFrance
  2. 2.CNRSClermont-FerrandFrance
  3. 3.IRDClermont-FerrandFrance
  4. 4.School of Geosciences, Monash UniversityClaytonAustralia

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