11 Using Volcanic Deposits to Help Us Understand Volcanic and Magmatic Processes

This session invites presentations that leverage volcanic deposits to reconstruct magmatic and eruptive processes. We welcome contributions from field and experimental volcanology, petrology, geochemistry, thermodynamics, and fluid mechanics, ranging from the landform to nanoscale.

Sunday, 19 October 2025
8:00 AM - 12:00 PM
HBGCC, 217A

Investigating the Effect of Nanolitization on Melt Viscosity using Raman Spectroscopy

Paper number: 11-11
Program: Technical Sessions
Time: 10:45 AM – 11:00 AM

Authors

Abstract

Crystallization of nanometer-sized crystal (nanolites) has been linked to increases in magma viscosity and bubble nucleation, which may enhance eruption explosivity. Here we utilize Raman microscopy to investigate the influence of oxide nanolite crystallization on the viscosity of obsidian lava from Eastern Australia. The base of rhyolite lava contains alternating bands of brown and colorless glass. Raman spectra were collected for over 130 brown glasses and 120 colorless glasses using a HORIBA XploRa Plus spectrometer and a 532-nm Nd laser at 50% intensity. The laser was focused through a 50x objective, using a 300-micrometer confocal pinhole and a 200-micrometer slit. All spectra were acquired using counting times of 3 x 30s and a grating of 1800 grooves per millimeter. Nanolite numbers and melt viscosities were derived following the models of Di Genova et al. (2018) Measuring the degree of “nanotilization” of volcanic glasses: Understanding syn-eruptive processes recorded in melt inclusions, Lithos, 318, 209-218, and Giordano et al. (2019) A calibrated database of Raman spectra for natural silicate glasses: implications for modelling melt physical properties, J. Raman Spectroscopy, 51, 1822-1838.

Our results show that melt viscosity increases with the degree of nanolitization, with colorless glasses generally characterized by lower nanolite numbers and viscosities compared to brown glasses. Moreover, the viscosity of colorless glass at the nanolite-poor end of the spectrum agrees with that estimated on (nanolite free) glass chemistry using the multicomponent viscosity model of Giordano et al. (2008) Viscosity of magmatic liquids: A model, Earth and Planetary Science Letters, 271, 123-134, and a magmatic temperature of 850°C. Although the observed increase in melt viscosity associated with nanolitization is consistent with chemical extraction of iron in oxide nanolites produced in experimental studies, our results demonstrate that even an order of magnitude increase in melt viscosity may not be sufficient to drive explosive fragmentation. Depending on ascent dynamics, nanolite formation may alternatively play a role in non-explosive shear fragmentation near conduit margins, enhancing magma degassing and promoting effusive activity.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-414892

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