The Importance of Sintering with Crystals in Volcanic Regimes

Sintering, or welding, in silicic volcanic conduits limits outgassing, and outgassing from these conduits has a first order effect on determining the explosivity of an eruption (Cassidy et al., 2018). Crystals in volcanic systems can act as rigid inclusions; particles that are not involved in the sintering process but can have a significant effect on porosity and permeability. However, the role of crystals in sintering in a volcanological context has rarely been investigated previously. Here, analogue glass and crystal mixtures were sintered in situ using 4D x-ray tomography data collected in real time at the Diamond Light Source JEEP (i12) beamline synchrotron. This non-destructive technique captures high resolution 3D images at multiple points allowing the visualisation and quantification of interior and exterior changes. The data were processed using a 3D visualisation software to quantify porosity and connectivity. When crystals are included in the starting mixture, the total porosity decreases, the disconnected porosity increases through the experiment, and the final porosity is higher with greater crystal content. The pore network preferentially disconnects through the z-axis first before pores are disconnected through other axes. A high connectivity is maintained to lower porosities (i.e. for a longer period of time) compared to crystal-free systems, suggesting that degassing is more efficient which may reduce the frequency of explosive events or quicken the transition to effusive behaviour. The results demonstrate that crystals do have an impact on sintering behaviour and further work is required to establish the effects of even greater crystal content and of different pressure conditions.