Is there a recipe for Plinian eruptions? Evidence from past events and analogous volcanoes.
Abstract:Eruption forecasting as pertains to temporal evolution of an eruption has been vastly improved by the advancement of monitoring techniques. It is still, however, difficult to anticipate how large or explosive is an eruption is likely to be. Moreover, we have very limited instrumental evidence for the precursory signs of Plinian eruptions. At a volcano that is known to have a history of moderate size events (VEI 3 - 4) interspersed with several VEI≥6 events, how do we prepare when the volcano enters into a period of unrest? Is it possible to isolate key activity that may indicate that this event is more or less likely to be a large, explosive event? Is there a recipe for Plinian eruptions? In this study we have compiled evidence of instrumental and non-instrumental data from 14 Plinian historical eruptions (including 23 different criteria) to isolate any common features of large explosive eruptions. We looked at: eruption prerequisites (e.g., repose time, presence of an exsolved gas phase, viscosity, and volatile gradients), additional conditions that must develop (fresh intrusions, magma mixing, ascent rates), Plinian potential (evidence of past Plinian eruptions, shear within the conduit, high magmatic volatiles) and finally any observed precursors that in combination may indicate a imminent Plinian eruption (seismicity: deep Long Period, Distal Volcano Tectonic earthquakes, high energy / long duration earthquake swarms, deformation: pronounced or prolonged inflation). Given the limted number of historical plinian eruptions, we supplemented our data set and conclusions with data from more than 30 other analogous volcanoes with subplinian events. We combine these datasets to look for commonalities to provide better – constrained probabilities for large (VEI≥6) eruptions.
Initial findings show that for 50% of the Plinian eruptions studied there is evidence of an exsolved gas phase. We also find that at least 58% of Plinian eruptions are preceded by phreatomagmatic eruptions that contain juvenile material and that in 78% of cases there is significant seismicity that increased in intensity prior to the eruption.