TY - JOUR
T1 - Does Bubble Nucleation Occur Heterogeneously in Magmas Feeding Explosive Rhyolite Eruptions? Insights From the Rock Magnetic Properties of Pumice
AU - McCartney, Kelly N.
AU - Hammer, Julia E.
AU - Shea, Thomas
AU - Brachfeld, Stefanie
AU - Giachetti, Thomas
AU - Houghton, Bruce F.
N1 - Publisher Copyright:
© 2025. The Author(s).
PY - 2025/8/28
Y1 - 2025/8/28
N2 - Nanometer-scale titanomagnetite crystals have been detected in nominally aphyric rhyolite pumice, but whether they are numerous enough to impact bubble nucleation in explosive silicic volcanism was unresolved. This study examines sub-micron crystals using rock magnetic techniques, Rhyolite-MELTS modeling, and physical characterization. We analyzed pumice from four eruptions spanning wide ranges in intensity, storage depth, and bubble number density (1016 to 1013 m−3 liquid): 1060 CE Glass Mountain, 1912 CE Novarupta, 232 CE Taupo, and 0.45 Ma Pudahuel. Calculations assuming monospecific assemblages of 10 and 1,000 nm cubic particles yield titanomagnetite number densities of 1021 to 1013 m−3 dense rock equivalent, respectively. In all cases, titanomagnetite is thermodynamically stable at pre-eruptive storage conditions and magnetic susceptibility (χLF) is independent of vesicularity and permeability, indicating that crystals likely formed prior to vesiculation. The existence of nm-scale Fe-Ti oxides in four diverse cases suggests that heterogeneous bubble nucleation is a general feature of explosive rhyolite volcanism.
AB - Nanometer-scale titanomagnetite crystals have been detected in nominally aphyric rhyolite pumice, but whether they are numerous enough to impact bubble nucleation in explosive silicic volcanism was unresolved. This study examines sub-micron crystals using rock magnetic techniques, Rhyolite-MELTS modeling, and physical characterization. We analyzed pumice from four eruptions spanning wide ranges in intensity, storage depth, and bubble number density (1016 to 1013 m−3 liquid): 1060 CE Glass Mountain, 1912 CE Novarupta, 232 CE Taupo, and 0.45 Ma Pudahuel. Calculations assuming monospecific assemblages of 10 and 1,000 nm cubic particles yield titanomagnetite number densities of 1021 to 1013 m−3 dense rock equivalent, respectively. In all cases, titanomagnetite is thermodynamically stable at pre-eruptive storage conditions and magnetic susceptibility (χLF) is independent of vesicularity and permeability, indicating that crystals likely formed prior to vesiculation. The existence of nm-scale Fe-Ti oxides in four diverse cases suggests that heterogeneous bubble nucleation is a general feature of explosive rhyolite volcanism.
KW - crystal and bubble number densities
KW - explosive rhyolite eruptions
KW - heterogeneous bubble nucleation
KW - magnetic characterization of pumice
KW - nanoscale magnetite particles
UR - https://www.scopus.com/pages/publications/105013775990
U2 - 10.1029/2025GL115789
DO - 10.1029/2025GL115789
M3 - Article
AN - SCOPUS:105013775990
SN - 0094-8276
VL - 52
JO - Geophysical Research Letters
JF - Geophysical Research Letters
IS - 16
M1 - e2025GL115789
ER -