Characterising pyroclastic density current grainsize data

Grainsize data is used across volcanology to aid interpretation of deposit trends and inform transport and depositional process. Collected grainsize data and the way it is presented varies for different processes, for example tephra fall versus pyroclastic density currents: grainsize information is more easily measured for fall deposits and is thus more available in the published record. This is related to the preservation and size distribution of a deposit. Pyroclastic density current (PDC) deposits are often focused in valleys and are therefore prone to rapid erosion and reworking and tend to have a much larger range in grainsize at a given location than tephra fall deposits. This relative lack of data, and differences in ways of data presentation, mean that it can be difficult to compare information from different events, and inform our understanding of PDC process. Here, we present a review of PDC grainsize data as presented in the published record. We analysed information from 175 papers, extracting grainsize information from 71 papers, covering 83 PDC events. Information collected includes whether grainsize distributions or statistics were presented, and their characteristics, for example bin size. Within these papers, there is a wide range in the way grainsize information is presented, from distribution statistics to complete distributions, and often using different units (for example phi and mm). Given the large range of clasts in PDC deposits, distributions are often truncated at the course and/or fine extent. There is also a wide range in how the data is visualised, for example use of median versus sorting coefficient, ternary plots and plots of fine proportions. We use insight from this metadata analysis to understand how different treatments of PDC grainsize data affect their interpretation and comparison of data from different eruptions and can provide different insights into PDC processes.