Simulating the behavior of volcanic ash during explosive eruptions in the laboratory to improve the accuracy of particle dispersion predictions is the aim of the study by INGV and the University of Munich, recently published in Scientific Reports
Is it possible to predict how and where the ashes emitted during an explosive volcanic eruption of Etna or Vesuvius will fall? A recent study, conducted by a team of researchers from the National Institute of Geophysics and Volcanology (INGV) of Rome, Pisa and Catania, in collaboration with the University of Munich, simulated the behavior of volcanic ash in the laboratory, improve the accuracy of predictions of particle dispersion during explosive eruptions. The study, Effect of particle volume fraction on the setting velocity of volcanic ash particles: insights from joint experimental and numerical simulations (http://www.nature.com/articles/srep39620), was published in Scientific Reports.
“Volcanic ash is made up of small fragments of glass and crystals” explains Jacopo Taddeucci, INGV researcher. “These particles are generated in large quantities during explosive volcanic eruptions. Released into the atmosphere, the particles form a volcanic cloud which is transported and dispersed by the winds, and then deposited on the ground even thousands of kilometers away and months after the eruption”.
Volcanic ash has deleterious effects on human health, the environment, and infrastructures (just remember the disruption to air traffic in 2010 due to the eruption of the Icelandic volcano Eyjafjallajökull).
"To know in advance where the ash will fall and in what quantities and, therefore, effectively deal with its effects", adds Elisabetta Del Bello, INGV researcher, "it is essential to know better the behavior of the ash in volcanic clouds and in the atmosphere . In this study, the behavior of the ash particles during the fallout was simulated in the laboratory, by filming the falling particles with special high-speed, high-definition cameras, and then reproducing the same experiments through mathematical models."
Thanks to this combined approach, the work has highlighted how the amount of ash falling from the volcanic cloud is able to modify the falling speed of the particles.
“The main implication of this discovery is that in the regions closest to an erupting volcano (less than 20-50 km, depending on the eruption), where the volcanic cloud is most heavily loaded with ash, the rate of particle fallout it can increase significantly, with the consequence of having a greater accumulation of ash on the ground, adds Del Bello.
The study also proposes a method to predict the rate of ash fall under such conditions. "This method", concludes Taddeucci, "will contribute to improve the accuracy of the predictions of ash dispersion during explosive eruptions".
Extended
Most of the current ash transport and dispersion models neglect particle-fluid (two-way) and particle-fluid plus particle-particle (four-way) reciprocal interactions during particle fallout from volcanic plumes. These interactions, a function of particle concentration in the plume, could play an important role, explaining, for example, discrepancies between observed and modeled ash deposits. Aiming at a more accurate prediction of volcanic ash dispersal and sedimentation, the settling of ash particles at particle volume fractions (ϕp) ranging 10−7-10−3 was performed in laboratory experiments and reproduced by numerical simulations that take into account first the two -way and then the four-way coupling. Results show that the velocity of particles settling together can exceed the velocity of particles settling individually by up to 4 times for ϕp ~ 10−3. Comparisons between experimental and simulation results reveal that, during the sedimentation process, the settling velocity is largely enhanced by particle-fluid interactions but partly hindered by particle-particle interactions with increasing ϕp. Combining the experimental and numerical results, we provide an empirical model allowing correction of the settling velocity of particles of any size, density, and shape, as a function of ϕp. These corrections will impact volcanic plume modeling results as well as remote sensing retrieval techniques for plume parameters.
Del Bello, E. et al. Effect of particle volume fraction on the setting velocity of volcanic ash particles: insights from joint experimental and numerical simulations. Sci. Rep. 7, 39620; doi:10.1038/srep39620 (2017).
The High Pressure - High Temperature Laboratory of Experimental Geophysics and Volcanology is located in the Rome headquarters of INGV. The person in charge is Piergiorgio Scarlato. Some of the leading INGV researches in the volcanological, seismic and environmental fields are carried out in the laboratory, some of which are financed as part of European projects. Many of the analytical and experimental activities of INGV are concentrated here in support of research and monitoring, but also the development of technologies and new survey methodologies. The most recent experimental activities, also carried out in collaboration with laboratories in other countries, concern simulations and measurements related to the physics of rocks and earthquakes, the chemical-physical properties of magmas, and the analog modeling of volcanic processes . The laboratory is also a pole of attraction for Italian and foreign researchers
Photo 1 - Iceland, Eyjafjallajökull eruption, May 2010: high-speed shots of the explosive activity on top of the glacier
Photo 2 - November 2002 Etna eruption: after strong explosions like this one, the ash plume often reaches the city of Catania
Photo 3 - Iceland, Eyjafjallajökull eruption, May 2010: sampling of the ash at the foot of the volcano. The researchers are enveloped in fine ash suspended in the air