Chedeville C., Roche Olivier. (2014). Autofluidization of pyroclastic flows propagating on rough substrates as shown by laboratory experiments. Journal of Geophysical Research.Solid Earth, 119 (3), p. 1764-1776. ISSN 2169-9313.
Titre du document
Autofluidization of pyroclastic flows propagating on rough substrates as shown by laboratory experiments
Journal of Geophysical Research.Solid Earth, 2014,
119 (3), p. 1764-1776 ISSN 2169-9313
This study investigates the influence of the substrate surface roughness on the emplacement mechanisms of pyroclastic flows. We carried out laboratory experiments on gravitational flows generated from the release of initially fluidized or nonfluidized columns of fine particles (diameter d = 0.08 mm) in a horizontal channel. The roughness of the channel base was uniform in each experiment, created by gluing particles of diameter d(0) = 0.08 to 6mm to the base. Other things being equal, the flow runout distance increased with the channel base roughness (d(0)) to a maximum of about twice that of flows on a smooth substrate when d(0) = 1.5-3 mm, before decreasing moderately at higher roughness values of d(0) = 6 mm. Long runout originated mainly during the late stages of emplacement as flow deceleration was strongly reduced at high substrate roughness. This was caused by (partial) autofluidization due to an upward air flux escaping from the substrate interstices in which flow particles settled. Autofluidization was evidenced by high pore fluid pressure measurements at the base of initially nonfluidized flows and also by reduced flow runout when the interstices were initially partially filled so that less air was available. Furthermore, the runout distance of flows of large particles (d = 0.35 mm), which could not be fluidized by the ascending air flux, was independent of the substrate roughness. This study suggests that autofluidization caused by air escape from the interstices of a rough substrate is one important mechanism to explain the common long runout distance of pyroclastic flows even on subhorizontal topographies.
