Likelihood of basaltic eruptions as a function of volatile content and volcanic edifice size

Abstract

A simple physical model is used to link eruption likelihood in continental regions to the size and shape of the volcanic edifice, as well as to magma density and volatile content. A volcanic edifice acts as a surface load and modifies the stress field in upper crustal levels including the magma chamber. It affects the critical magma overpressure for reservoir failure as well as the conditions of dyke ascent from reservoir to surface. Calculations are made for dyke ascent in the stress field due to an overpressured reservoir beneath an edifice. Different edifice shapes are investigated, from shield volcanoes with gentle slopes to stratovolcanoes with steeper flanks. Beneath a mature volcanic edifice, magmatic overpressures required for reservoir failure are large, but not large enough for a dyke to reach the central vent area at the summit. Thus, basaltic summit eruptions can only occur if the amount of dissolved volatiles exceeds some threshold value which increases with edifice size, and hence must be in explosive regimes unless magma is able to degas at shallow depths. For mature volcanic systems, edifice collapse or destruction may lead to renewed basaltic activity through the central vent area.