PETROLOGICAL INSIGHT INTO THE INITIATION OF VOLCANIC ERUPTIONS AT SUBDUCTION ZONE VOLCANOES
Petrological approaches are particularly amenable to studying initiation in both modern and prehistoric eruptions. Initiation typically involves some of the last high temperature processes that affect erupted magmas, and these often leave clear signals preserved in the petrographic record. Petrological techniques are also increasingly providing access to the timescales of eruption initiation, which are important for evaluating future volcanic hazards and the societal response to eruptive episodes.
We present a survey of eruption initiation mechanisms deduced from petrology and other observations for selected subduction zone volcanoes. A number of different mechanisms are evident, including endogenous processes related to magma recharge, magma mixing and vapor accumulation or second boiling and exogenous process related to far field events like earthquakes. Timescales associated with initiation, including the time between recognition of volcanic unrest via seismic, gas or other remote means, and the time at which magma breaches the surface, appear to range between weeks and months, similar to the run up times identified from seismic unrest.