Multi-stage volcanic events: a statistical investigation

Volcanic events comprising multiple eruptive stages are common in the historical and geological record and display activity of variable intensity ranging, in some cases, through to several centuries. To better understand the characteristics of such events globally, this study explores a database of historical events having Volcanic Explosivity Indices 4 or greater. The database was compiled for the most part from published and unpublished material provided by the Smithsonian Institution. The database was examined to find common statistical relationships, within and between the variables characterising multi-stage explosive events. In concert with common usage, an event is defined here as clearly related activity over days to years whereas a stage represents a shorter duration (hours to weeks) characterised by one distinct style of activity. Over half of all volcanic events investigated exhibited more than one explosive stage and 77% of these stages occurred within the first 10% of the total defined duration of the event. This investigation confirmed a general eruptive pattern of declining explosivity with time and reaffirmed a positive correlation between stage column height and volume. Distributions presented in this paper are a first step towards describing the general patterns displayed by multi-stage events; however, it must be cautioned that they may be applicable neither for any particular volcanic centre nor across all eruptive scales and styles.