Standardized analysis of juvenile pyroclasts in comparative studies of primary magma fragmentation; 1. Overview and workflow

Abstract

Juvenile pyroclasts, especially in the ash size range, provide important information on primary fragmentation processes, i.e. initial explosive magma fragmentation, and on the state of the magma both prior to and at the point of fragmentation and quenching. There exists an extensive body of literature focusing on the quantification of juvenile particle morphology (shape), internal textures and surface features spanning several decades, however a standardized method has yet to emerge for comparative studies. No community-wide consensus currently exists (i) regarding the most representative size fraction(s) to be examined, (ii) on sample preparation procedures (such as whether to use whole particle silhouettes or 2D cross-sections), (iii) on imaging techniques and image acquisition parameters, or (iv) on the optimal morphometric parameters to measure. Lack of a standardized method precludes robust comparison between different studies and laboratories. We propose here a preliminary "best practices" and workflow for characterization of juvenile pyroclasts, for comparative studies of primary fragmentation. If the community follows such a standardized method, it will become possible to accumulate a large volume of consistent data on juvenile pyroclasts from a range of eruption styles, fragmentation mechanisms, and magma compositions. This will ultimately allow deeper insights into the full panoply of magma-to-pyroclast processes that drive particle-producing volcanic eruptions. One or more "fragmentation diagrams" may eventually be developed to allow different types of magmatic and phreatomagmatic explosive eruptions to be distinguished based on their products.

Physical and morphological characterization of the 19 May 2021 ash cloud deposit at Stromboli (Italy)

“…Bulk samples were mounted in epoxy resin and polished for componentry, textural and geochemical analyses, following the procedures described by Ross et al 74 . These analyses were performed at the Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa (INGV-Pisa) by using a scanning electron microscope (SEM) Zeiss EVO MA.…”

VolcashDB: Volcanic ash particle image and classification database

“…Using the observational features noted above -not to confuse with the 33 extracted features-, each particle was classified into the four main types that are typically used in the literature (e.g., Gaunt et al, 2016;Suzuki et al, 2013;Ross et al 2022): free crystals, altered material, lithic, and juvenile; we also classified the particles into a few sub-types (Table 4).…”

“…We thus also observed these particles using the SEM. We looked for homogeneous grayscale, smooth surface, sharp or stepped edges (Pardo et al, 2020;Ross et al, 2022), and the lack of signs of weathering (e.g., etch pitting). Juvenile particles were further classified based on crystallinity and color, and based on the shape and presence of hydrothermal material on surfaces.…”

Magmatic and phreatomagmatic contributions on the ash-dominated basaltic eruptions: Insights from the April and November–December 2005 paroxysmal events at Karthala volcano, Comoros

“…All the samples were systematically dried in the oven at 70°C for 48 hours. This low temperature drying step preserved any potential phases present on the samples, eased the manual sieving and allowed to perform accurate density measurements (Ross et al, 2022).…”