Determining the porosity of pyroclasts: Comparing approaches to reveal magma textures

Volcanic eruptions are driven by magma rising through Earth’s crust. The style of an eruption depends on intrinsic and extrinsic parameters and is commonly a dynamic process. Thorough investigation of the related products is fundamental to understanding eruptive phenomena.In this context, quantitatively constraining the dispersal area, grain size distribution and pyroclast textures is essential. Volume determination of pyroclasts is fundamental to constrain density and porosity. However, volume determination of irregularly shaped pyroclast cannot be done with geometrical laws but hat to be assessed with different methodologies. In this study, we have collected a set of clasts from Santorini, Greece, to test three methodologies: a manual methodology to measure three orthogonal axes with a calliper; an optical methodology to measure longest and shortest axis through multiple photographs; and the Archimedean methodology.All three methodologies found similar volume results with little impact on the subsequent assessment of porosity and density. The discrepancy between Archimedean and manual/optical methodologies is observed to be smaller than the revealed natural variability. For this reason, we advertise the manual methodology to be used for future field campaigns as a simple and fast yet reliable approach to gain insights into the textural state of magma at eruption.
The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)