Publication Date:
2020-12-14
Description:
Pyroclast ejection during explosive volcanic eruptions occurs under highly dynamic conditions
involving great variations in flux, particle sizes, and velocities. This variability must be a direct consequence
of complex interactions between physical and chemical parameters inside the volcanic plumbing system.
The boundary conditions of such phenomena cannot be fully characterized via field observation and
indirect measurements alone. In order to understand better eruptive processes, we conducted scaled and
controlled laboratory experiments. By performing shock-tube experiments at known conditions, we defined
the influence of physical boundary conditions on the dynamics of pyroclast ejection. If applied to nature, we
are focusing in the near-vent processes where, independently of fragmentation mechanism, impulsively
released gas-pyroclast mixtures can be observed. These conditions can be met during, e.g., Strombolian or
Vulcanian eruptions, parts of Plinian eruptions, or phreatomagmatic explosions. The following parameters
were varied: (1) tube length, (2) vent geometry, (3) particle load, (4) temperature, and (5) particle size
distribution. Gas and particles in the experiments are not coupled (St 〉〉 1). The initial overpressure, with
respect to atmosphere, was always at 15 MPa. We found a positive correlation of pyroclast ejection velocity
with (1) particle load, (2) diverging vent walls, and (3) temperature as well as a negative correlation with (1) tube
length and (2) particle size. Additionally, we found that particle load strongly affects the temporal evolution
of particle ejection velocity. These findings stress the importance of scaled and repeatable laboratory
experiments for a better understanding of volcanic phenomena and therefore volcanic hazard assessment.
Description:
Published
Description:
6031 – 6045
Description:
5V. Dinamica dei processi eruttivi e post-eruttivi
Description:
JCR Journal
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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