EGU2020-17732
https://doi.org/10.5194/egusphere-egu2020-17732
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

The effect of nanolites on degassing of silica-rich magma

Francisco Cáceres1, Fabian Wadsworth2, Bettina Scheu1, Mathieu Colombier1, Claudio Madonna3, Corrado Cimarelli1, Kai-Uwe Hess1, Melanie Kaliwoda4, Bernhard Ruthensteiner5, and Donald B. Dingwell1
Francisco Cáceres et al.
  • 1Earth and Environmental Sciences, Ludwig-Maximilians-Universität (LMU) München, Germany (f.caceres@lmu.de)
  • 2Department of Earth Sciences, Durham University, UK
  • 3Department of Earth Sciences, ETH Zürich, Switzerland
  • 4Mineral State Collection Munich, Germany
  • 5Zoologische Staatssammlung München, Germany

Magma degassing dynamics play an important role controlling the explosivity of volcanic eruptions. Some of the largest explosive eruptions in history have been fed by silica-rich magmas in volcanic systems with complex dynamics of volatiles degassing. Degassing of magmatic water drives bubble nucleation and growth, which in turn increases magma buoyancy and results in magma ascent and an eventual eruption. While micro- to milli-meter sized crystals are known to cause heterogeneous bubble nucleation and to facilitate bubble coalescence, the effects of nanolites remains mostly unexplored. Nanolites have been hypothesized to be a primary control on the eruptive style of silicic volcanoes, however the mechanisms behind this control remains unclear.

Here we use an experimental approach to show how nanolites dramatically increase the bubble number density in a degassing silicic magma compared to the same magma without nanolites. The experiments were conducted using both nanolite-free and nanolite-bearing rhyolitic glass with different low initial water content. Using an Optical Dilatometer at 1 bar ambient pressure, cylindrical samples were heated at variable rates (1-30 °C min-1) to final temperatures of 820-1000 °C. This method allowed us to continuously monitor the volume, and hence porosity evolution in time. X-ray computed microtomography (µCT) and Scanning Electron Microscope (SEM) analyses revealed low and high bubble number densities for the nanolite-free and nanolite-bearing samples respectively.

Comparing vesicle number densities of natural volcanic rocks from explosive eruptions and our experimental results, we speculate that some very high naturally occurring bubble number densities could be associated with nanolites. We use a magma ascent model with P-T-H2O starting conditions relevant for known silicic eruptions to further underpin that such an increase in bubble number density caused driven by the presence of nanolites can feasibly turn an effusive eruption to an eventually explosive behavior.

How to cite: Cáceres, F., Wadsworth, F., Scheu, B., Colombier, M., Madonna, C., Cimarelli, C., Hess, K.-U., Kaliwoda, M., Ruthensteiner, B., and Dingwell, D. B.: The effect of nanolites on degassing of silica-rich magma, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17732, https://doi.org/10.5194/egusphere-egu2020-17732, 2020