The Agnano–Monte Spina (AMS) eruption, which occurred approximately 4,100 years ago, was the largest volcanic event of the most recent period of activity in the Campi Flegrei caldera—an area now densely populated. This eruption serves as a crucial reference for assessing future volcanic activity and developing risk mitigation strategies, especially given the increasing activity detected by current monitoring systems. In this study, we investigate the melt viscosity and short-range structure of the liquid phase in erupted magmas, to better understand the relationship between the physicochemical properties of magma and the structure of volcanic melts.

High-pressure and high-temperature experiments (using the piston-cylinder and TZM apparatuses) were conducted to synthesize AMS trachyte with varying water contents (0.5–4.5 wt.%). In some cases, the synthesized silicate glasses exhibited nano-crystallization, potentially caused by intrinsic melt structure properties (e.g., diffusivity, solubility), variations in oxygen fugacity and water content. The melt viscosity was derived using conventional and flash differential scanning calorimetry measurements (C- and F-DSC), enabling the development of comprehensive viscosity models combined with the literature data. Preliminary results from DSC analyses of AMS trachyte show that the glass transition temperature (where the melt viscosity is equal to 10^12 Pa s) decreases from 562 °C to 350 °C as water content increases from 0.5 to 4.5 wt.%. In addition, Raman spectroscopy will be used to examine the structural changes in hydrous melts and to assess possible changes induced by high-temperature C- and F-DSC measurements.

Using DSC-derived viscosity data combined with Raman spectroscopy, this study proposes to examine how both melt structure properties and crystallization influence changes in magma viscosity over a range of high temperatures typical of volcanic eruptions. These findings will provide vital insights into the factors that control the explosivity and eruptive behavior of trachytic magmas at Campi Flegrei.