Experimental modeling of volcano explosive activity.
The NEMOH’s fellow Damien Gaudin took part of an experiment that gains a page on the NATURE news of May.
Damien, what is the topic of this experiment?
The primarily goal of the experiment is to have a multidisciplinary approach of the dynamics of the volcanic explosions and its effects, by making a series of twelve explosions in a artificially layered material.
How was composed the group where you carried out the experiment and what role did you play?
It was an international group lead by the Geohazard group of the University at Buffalo (NY), including scientists from Europe, America and Oceania. Some of them were interested on geophysical signals generated by the explosions (imagery, acoustics, seismology, electricity, etc.) while others were more focused on the geological consequences of the explosions (crater topography and shape of the geological layers). I was part of a group that monitored the explosions with optical and thermal high-speed cameras. Ping-pong and tennis balls filled with different materials were set at the surface of the layered material to reproduce volcanic bombs that are ejected by strombolian and vulcanian explosions. We monitored their trajectories from the initial acceleration to their settling.
Why is it important to predict the trajectory of the ballistic products and, more in general, why is it so relevant carrying out that kind of experiments?
Ballistic hazard is of crucial interest on explosive volcanoes as Stromboli where dozens of tourists approach the crater each night. Besides the field observations and computer models, experimental modeling have a crucial interest for understanding these explosive phenomena since they can be very well defined and controlled. This experiment was also highly monitored, allowing a multidisciplinary approach of the phenomena.
What results have you obtained?
Preliminary analysis of the videos shows that the balls are accelerated jointly with the surface during the first hundredth of seconds of the ground expansion. Then, they escape from the top of the sand cloud, due to their higher inertia moment that reduces the effects of drag. The localization of the impact points of the balls shows they traveled much further than the finer particles. One of these balls landed close to a seismic station ~100 m from the blast, allowing to precisely estimate its time travel: 8 seconds, corresponding to a initial vertical velocity greater than 40 m/s.
What are now the next steps?
The videos will be further analyzed in order to better characterize the acceleration and the ballistic phases of these artificial volcanic bombs.
A video of the experiment can be see at the following link:
http://www.nature.com/news/experimental-volcanoes-make-a-blast-1.12970
