A proxy for magmatic foams: FOAMGLAS®, a closed-cell glass insulation

FOAMGLAS® is a closed-cell glass insulation that has a high porosity, is impermeable, and can be heated above its glass transition temperature (Tg) without fracturing. Here, we characterize, using standard laboratory techniques, the thermal and transport properties of FOAMGLAS®, and report viscometry and calorimetry results. Based on this characterization, we propose that FOAMGLAS® be used as a proxy material in studies of the deformational behaviour of natural crystal-free melts populated with isolated bubbles. We demonstrate its utility with a case study: cores of FOAMGLAS® are deformed at high temperature (>Tg) in uniaxial compression. Deformed FOAMGLAS® samples record a different pattern of strain accumulation (volume loss vs. bulging) compared to deformed natural materials where bubble connectivity is high (e.g., sintered ash, vesicular lavas). The divergent behaviour can be ascribed to pressurization of the isolated gas-filled bubbles as a result of compression. The pressurized bubbles resist deformation, and expand when unloaded. In contrast, the high connectivity of open-cell foams allows gas escape and collapse of pore space during compression. The different behaviours of open- and closed-cell melt foams highlight the influence of isolated bubbles on magma rheology. These results demonstrate the utility of FOAMGLAS® as an experimental analogue for closed-cell bubble-rich magmas.