Estimating the viscosity of volcanic melts from the vibrational properties of their parental glasses

Abstract

The numerical modelling of magma transport and volcanic eruptions requires accurate knowledge of the viscosity of magmatic liquids as a function of temperature and melt composition. However, there is growing evidence that volcanic melts can be prone to nanoscale modification and crystallization before and during viscosity measurements. This challenges the possibility of being able to quantify the crystal-free melt phase contribution to the measured viscosity. In an effort to establish an alternative route to derive the viscosity of volcanic melts based on the vibrational properties of their parental glasses, we have subjected volcanologically relevant anhydrous glasses to Brillouin and Raman spectroscopic analyses at ambient conditions. Here, we find that the ratio between bulk and shear moduli and the boson peak position embed the melt fragility. We show that these quantities allow an accurate estimation of volcanic melts at eruptive conditions, without the need for viscosity measurements. An extensive review of the literature data confirms that our result also holds for hydrous systems; this study thus provides fertile ground on which to develop new studies of the nanoscale dynamics of natural melts and its impact on the style of volcanic eruptions.

A chemical threshold controls nanocrystallization and degassing behaviour in basalt magmas

“…2). We therefore used T g and m derived elsewhere by calorimetry and Brillouin spectroscopy 36 . Literature data enabled the very accurate description of high-temperature concentric-cylinder data (Fig.…”

“…We attribute this difference to small but significant differences in total iron and titanium content, which can dramatically affect the tendency of the magmas to reach oversaturation in the vicinity of T g and (nano)crystallize. We thereby emphasize the need for a critical review and validation of the published viscosity data, providing a vademecum for correct experimental determination of viscosity based on our previous studies 32,36 .…”

“…Only in the last 4 years, 60 studies 21,23,[31][32][33][34][35][36] have been published reporting or inferring the presence of nanocrystals in natural and synthetic samples (Fig. 1).…”

New insights about the role of Na–K ratio on the vibrational dynamics of synthetic‐basalt glasses

“…[33] Recently, it has been demonstrated that the BP position and the ratio of the bulk and shear moduli of volcanic and technical glasses correlate firstly with their parental melt fragility and secondly with the system chemistry, thus allowing an accurate estimation of the melt viscosity. [35] Here, we present a thorough characterization of four synthetic anhydrous basaltic glasses, showing the effect of Na-K mixing on their glass transition temperatures (T g ), resulting structures and the dynamical properties such as the BP. The composition of our samples mimics the overall percentage distribution of the chemical constituents of basalts on Earth [36] and explores a M a range (4.1 ≤ M a ≤ 4.8), which has identified optimal for CBFs manufacturing.…”

“…[ 33 ] Recently, it has been demonstrated that the BP position and the ratio of the bulk and shear moduli of volcanic and technical glasses correlate firstly with their parental melt fragility and secondly with the system chemistry, thus allowing an accurate estimation of the melt viscosity. [ 35 ]…”