Using a synthetic magma similar to the Phlegrean one, the viscosity and its ascent rate from the deepest layers of the Earth were calculated
The speed with which magma forms and rises from the depths of the Earth to the surface also depends on its viscosity and it is therefore of fundamental importance to know this physical property of magma also in order to define scenarios and estimates of hazard and connected volcanic risk.
With an experimental study, an international team of researchers led by Barbara Bonechi and Vincenzo Stagno of the Department of Earth Sciences of the Sapienza University of Rome, and conducted with the National Institute of Geophysics and Volcanology (INGV), Ehime University in Japan, Argonne National Laboratory in the USA (ANL) and the University of Trieste (UniTS), has developed estimates of the ascent speed of the magma of the Campi Flegrei system from the mantle source, which the authors place at a depth of about 60 km for their experiment. towards a hypothesized crustal feeding system of the caldera located 25 km. In the study "Experimental measurements of the viscosity and melt structure of alkali basalts at high pressure and temperature" just published in 'Scientific Reports', the scientists calculated that the average rising speed of magma in the aforementioned deepest region of the volcanic system is approximately 2.5-3 meters per year, considering a time interval of about 20 years between the major historical eruptions that took place in the Campi Flegrei region ("Ignimbrite Campana" from 39000 years ago and "Yellow Neapolitan Tufo" from 15000 years ago). They therefore hypothesized that the mantle spring could be found at a depth of about 60 km.
"We used a synthetic magma made by melting lava from the Solchiaro volcanic deposit, from the volcano of the same name formed in Procida about 17-19000 years ago”, explain Barbara Bonechi and Vincenzo Stagno. "The experiments, which we carried out at the prestigious Argonne National Lab synchrotron in Chicago, were aimed at determining the viscosity of magma at high pressures and temperatures".
Volcanic eruptions are superficial phenomena that represent the final stage of the life of a magma from its formation in the interior of the Earth to its migration towards the surface.
The volcanic hazard of an area is, among other things, connected to the explosivity of an eruption which depends on various factors including the chemical composition of the rising magma, the amount of gas released from it and any interaction with surface waters. An important role on the eruptive style of a volcano is therefore also given by the density and viscosity of a magma, the knowledge of which helps to improve the evaluations of the processes related to magmatic dynamics and to reduce the uncertainties on the modeling of these processes.
The researchers state “It is important that geochemical and seismological models consider the depth of formation of magmas and their potential rate of ascent. Using the technique of the falling sphere whose fall can be observed in real time through X-ray radiography produced by an accelerated beam of particles at the Argonne National Lab, we have been able to detect that the viscosity of the rising basaltic magma which feeds the system of Campi Flegrei varies between 0.5 and 3 Pascal according to".
Luca Ziberna, professor of petrology and petrography at the University of Trieste, dealt in particular with the redox conditions of lava, a fundamental chemical parameter for understanding magmatic processes. At the Department of Mathematics and Geosciences of the Julian University, some theoretical and experimental models have been studied which are useful for understanding the effect of the chemical composition, with particular reference to the oxidation state of iron, on the rising processes of magmas.
In the words of Bonechi and Stagno, concluding "The experimental data presented in this article are of absolute importance in the study of Campi Flegrei and constitute further information to integrate the geochemical data and geophysical models available today".
A contribution that could be useful in the future to refine the forecasting and prevention tools of civil protection but which at the moment has no direct implication on measures concerning the safety of the population.
Research link:
“Experimental measurements of the viscosity and melt structure of alkali basalts at high pressure and temperature. Sci Rep 12, 2599 (2022).
https://www.nature.com/articles/s41598-022-06551-7 - Bonechi, B., Stagno, V., Kono, Y. et al.
Figure 1. Landsat satellite image (https://volcano.si.edu/gallery/ShowImage.cfm?photo=GVP-01511) showing the Campi Flegrei caldera north of the Gulf of Naples. The caldera is 13 km wide, and is the result of continuous explosive eruptions between 34.000 and 12.000 years ago. The most recent eruption is that of 1538.
Figure 2. Model of magma ascent from the source to the Campi Flegrei feeding system.