Publications des scientifiques de l'IRD

Girolami L., Druitt T. H., Roche Olivier, Khrabrykh Z. (2008). Propagation and hindered settling of laboratory ash flows - art. no. B02202. Journal of Geophysical Research Solid Earth, 113 (B2), p. NIL_1-NIL_13. ISSN 0148-0227.

Titre du document
Propagation and hindered settling of laboratory ash flows - art. no. B02202
Année de publication
2008
Type de document
Article référencé dans le Web of Science WOS:000253533500001
Auteurs
Girolami L., Druitt T. H., Roche Olivier, Khrabrykh Z.
Source
Journal of Geophysical Research Solid Earth, 2008, 113 (B2), p. NIL_1-NIL_13 ISSN 0148-0227
The fluidal behavior of pyroclastic flows is commonly attributed to high gas pore pressures and associated fluidization effects. We carried out experiments on flows of fluidized volcanic ash at 170 degrees C, which is hot enough to reduce cohesive effects of moisture. The flows were generated in a 3- m- long, horizontal lock- exchange flume. The ash was fluidized and expanded uniformly in the flume reservoir by up to 43% above loose packing and was then released. Each flow defluidized progressively down the flume until motion ceased. Initial expansion E and initial height h(0) were varied independently of one another. The flows traveled in a laminar manner. Flow fronts exhibited three main phases of transport: ( 1) a brief initial phase of gravitational slumping, ( 2) a dominant, approximately constant velocity phase, and (3) a brief stopping phase. Phase 2 frontal velocities scaled with root gh(0), like other types of dam- break flow. Deposition from initially expanded flows took place by progressive sediment aggradation at a rate that was independent of distance and varied only with E. Despite rates of shear up to 80 s(-1), aggradation rates were identical to those determined independently, at the same value of E, in quasi-static collapse tests. Sedimentation caused the flows to thin progressively during transit until they ran out of volume. The dynamics were governed to a first order by two dimensionless parameters: (1) the initial aspect ratio h(0)/x(0) in the lock reservoir and (2) the ratio t(sett)/t(grav) of two timescales: a particle settling time t(sett) and a gravitational acceleration time t(grav).
Plan de classement
Géophysique interne [066]
Localisation
Fonds IRD [F B010046766]
Identifiant IRD
fdi:010046766
Contact