Ross, Pierre-Simon; White, James D. L.; Zimanowski, Bernd; Büttner, Ralf
(2008).
Multiphase flow above explosion sites in debris-filled
volcanic vents: insights from analogue experiments
Journal of Volcanology and Geothermal Research
, vol. 178
, nº 1.
p. 104-112.
DOI: 10.1016/j.jvolgeores.2008.01.013.
Résumé
Discrete explosive bursts are known from many volcanic eruptions. In maar-diatreme eruptions, they have occurred in
debris-filled volcanic vents when magma interacted with groundwater, implying that material mobilized by such
explosions passed through the overlying and enclosing debris to reach the surface. Although other studies have
addressed the form and characteristics of craters formed by discrete explosions in unconsolidated material, no details
are available regarding the structure of the disturbed debris between the explosion site and the surface. Field studies of
diatreme deposits reveal cross-cutting, steep-sided zones of non-bedded volcaniclastic material that have been inferred
to result from sedimentation of material transported by "debris jets" driven by explosions. In order to determine the
general processes and deposit geometry resulting from discrete, explosive injections of entrained particles through a
particulate host, we ran a series of analogue experiments. Specific volumes of compressed (0.5-2.5 MPa) air were
released in bursts that drove gas-particle dispersions through a granular host. The air expanded into and entrained
coloured particles in a small crucible before moving upward into the host (white particles). Each burst drove into the
host an expanding cavity containing air and coloured particles. Total duration of each run, recorded with high-speed
video, was approximately 0.5-1 second. The coloured beads sedimented into the transient cavity. This same behaviour
was observed even in runs where there was no breaching of the surface, and no coloured beads ejected. A steep-sided
body of coloured beads was left that is similar to the cross-cutting pipes observed in deposits filling real volcanic vents,
in which cavity collapse can result not only from gas escape through a granular host as in the experiments, but also
through condensation of water vapour. A key conclusion from these experiments is that the geometry of cross-cutting
volcaniclastic deposits in volcanic vents is not directly informative of the geometry of the "intrusions" that formed
them. An additional conclusion is that complex structures can form quickly from discrete events.
Actions (Identification requise)
 |
Modifier la notice |
Statistiques de téléchargement
Statistiques de téléchargement