Publications des scientifiques de l'IRD

Rowley P. J., Roche Olivier, Druitt T. H., Cas R. (2014). Experimental study of dense pyroclastic density currents using sustained, gas-fluidized granular flows. Bulletin of Volcanology, 76 (9), art. 855 [13 p.]. ISSN 0258-8900.

Titre du document
Experimental study of dense pyroclastic density currents using sustained, gas-fluidized granular flows
Année de publication
2014
Type de document
Article référencé dans le Web of Science WOS:000341366100006
Auteurs
Rowley P. J., Roche Olivier, Druitt T. H., Cas R.
Source
Bulletin of Volcanology, 2014, 76 (9), art. 855 [13 p.] ISSN 0258-8900
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 mu m) particles from a hopper; the falling particles impacted an impingement surface at concentrations of similar to 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 ms-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.
Plan de classement
Géophysique interne [066]
Localisation
Fonds IRD [F B010062516]
Identifiant IRD
fdi:010062516
Contact