Please use this identifier to cite or link to this item: http://hdl.handle.net/2122/11585
Authors: Stock, Michael J.* 
Humphreys, Madeleine C. S* 
Smith, Victoria C.* 
Isaia, Roberto* 
Pyle, David M.* 
Title: Late-stage volatile saturation as a potential trigger for explosive volcanic eruptions
Issue Date: 2016
Series/Report no.: /9 (2016)
DOI: 10.1038/ngeo2639
URI: http://hdl.handle.net/2122/11585
Keywords: explosive volcanic eruptions
magma evolution
volatile saturation
Abstract: Magma reservoirs are thought to grow relatively slowly, assembling incrementally under volatile-saturated conditions. Eruptions may be triggered by injections of volatile-rich melt, or generation of over-pressure due to protracted crystallization. Here, we analyse fluorine, chlorine and water in apatite crystals trapped at di erent stages of magma evolution, and in melt inclusions from clinopyroxene and biotite crystals expelled during an explosive eruption of the Campi Flegrei caldera, Italy, about 4,000 years ago. We combine our geochemical analyses with thermodynamic modelling to reconstruct the evolution of magmatic volatile contents leading up to the explosive eruption. We find that the magma reservoir remained persistently water-undersaturated throughout most of its lifetime. Even crystals in contact with the melt shortly before eruption show that the magma was volatile-undersaturated. Our models suggest that the melt reached volatile saturation at low temperatures, just before eruption.We suggest that late-stage volatile saturation probably triggered the eruption, and conclude that ‘priming’ of the magma system for eruption may occur on timescales much shorter than the decadal to centennial timescales thought typical for magma reservoir assembly. Thus, surface deformation pulses that record magma assembly at depth beneath Campi Flegrei and other similar magmatic systems may not be immediately followed by an eruption; and explosive eruptions may begin with little warning.
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