Volcanic eruption triggers: A hierarchical classification

Assessing the relative importance of various triggers of volcanic eruptions has been hampered because of the lack of a general model that allows a quantitative comparison in an unbiased form. In this paper the most important triggers of volcanic eruptions are examined using a general reference framework that visualizes volcanic eruptions as the final event on a chain of causality. Based on this general framework, a hierarchical classification of triggers is proposed. First and second order triggers are defined as processes capable to initiate the rupture of the walls of a magma reservoir, regardless of whether the tapped magma can reach the surface or not. Third order triggers are those taking place only after the rupture of the walls of a magma reservoir has occurred, but are important in determining whether the tapped magma actually reaches the surface. A fundamental trigger is defined as any first order trigger that also can provide enough energy to feed a volcanic eruption even in the absence of third order triggers. The assessment of the relative importance of triggers is done by considering the whole range of depths from which a volcanic eruption is likely to have been fed, including magma reservoirs located deeper than 150 km, even when these eruptions might be relatively uncommon in the geological record.