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A subtle chemical tipping point governs the eruption style of rhyolitic magmas

A team of researchers from the Institut de Physique du Globe de Paris and the University of Munich have just revealed in Nature that nanoscale changes in magma can cause catastrophic changes in the dynamics of volcanic eruptions, which can alternate between effusive and explosive eruptions.

A subtle chemical tipping point governs the eruption style of rhyolitic magmas

Publication date: 08/01/2018

Press, Research

Related teams :
Geomaterials

Related themes : Natural Hazards

What if certain major climate catastrophes were the result of changes in the eruptive style of rhyolitic volcanoes, which can alternate between effusive and explosive eruptions? An international team of researchers from the Institut de Physique du Globe in Paris and the University of Munich has revealed that changes that can occur on a nanoscale can cause major changes in eruptive dynamics. Three key factors combine to modify the structure and viscosity of a magma, leading to changes in eruptive dynamics:

  • an increase in the ratio, RK=K/(Na+K) causes an increase in viscosity of several orders of magnitude (Le Losq et al, 2017 Scientific Report)
  • the agpaititic rheological index, RAI=(Na2O+K2O+MgO+CaO+FeO)/(Al2O3+Fe2O3) for which values below 1 are correlated with high viscosities
  • the presence of iron oxide nanolite will also increase viscosity
Transition from effusive to explosive eruption, as seen by RAI versus RK diagrams

By observing how RAI and RK ratios vary over dozens of volcanic eruptions, both effusive and explosive, the Franco-German team has just shown that the most explosive eruptions are observed for RAI ratios of less than 1 and RK ratios of more than 0.5. This work shows that minute changes in the chemical composition of a rhyolitic magma have a first-order effect on viscosity, unlike water content or the presence of crystals.

Ref : “A compositional tipping point governing mobilization and eruption style of rhyolitic magma” – D. Di Genova, S. Kolzenburg, S. Wiesmaier, E. Dallanave, D. R. Neuville, K. U. Hess & D. B. Dingwell. Nature. doi:10.1038/nature24488

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