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A geochemical clock to measure timescales of volcanic eruptions

Final Report Summary - CHRONOS (A geochemical clock to measure timescales of volcanic eruptions)

The extent to which volcanic eruptions can be adequately assessed depends on how the underlying physical conditions and processes are understood. In the last years, our planet has been affected drastically by volcanic eruptions in a unique way in history. Eyjafjall (2010) and Grímsvötn (2011) volcanoes in Iceland and Calbuco (2015) volcano in Chile paralysed air traffic in Europe and South America demonstrating the enormous impact of even relatively low energy volcanic eruptions on a globalized society. In order to be prepared for all eventualities of future eruptions, we must understand not only how volcanoes work, but also quantify the eruptive timescales.
The ERC Consolidator Grant CHRONOS “A geochemical clock to measure timescales of volcanic eruptions” was an interdisciplinary project designed to address one of the most fundamental, yet poorly constrained, variable of volcanic eruptions: time. The project was hosted at the University of Perugia (Italy) and was composed by a group of scientists with different background (geologists, petrologists, geochemists, mineralogists, experimentalists, geophysicists) working together towards the common objective of determining timescales of explosive volcanic eruptions.
The most energetic eruptions occurred on planet Earth in the last two centuries have been triggered by refilling of a felsic volcanic magma chamber by a hot and more mafic magma, causing mixing between magmas. CHRONOS used the compositional heterogeneity produced by magma mixing, and frozen in time in the rocks, the same way a broken clock at a crime scene can be used to determine the time of the incident. In order to read this clock, the physico-chemical processes governing the mixing process must be well understood.
During the five years of CHRONOS project activities we have: a) carried out field campaigns and sample collection on a representative number of active volcanoes (Mt. Vesuvius, Phlegrean Fields, Aeolian Islands, Soufriere Hills, Mt. Calbuco) to study the compositional variability triggered by mixing before/during eruptions; b) designed and building a unique experimental device (the ChaOtic Magma Mixing Apparatus, COMMA) that can replicate with precision the magma mixing process at conditions relevant for volcanic systems; c) installed a state-of-the-art laboratory for the high-resolution geochemical analyses of the composition of both natural and experimental samples; d) defined empirical relationships, obtained from magma mixing experiments and based on the relative mobility of chemical elements, to determine the time elapsed between the onset of magma mixing and beginning of eruptions.
These lines of integrated research have been creating an unprecedented knowledge into the physical and chemical conditions characterizing magma mixing. This allowed us to build the first chronometer for volcanic eruptions based on the use of many chemical elements converging to the same timescale. The application of this chronometer to estimate eruption timescales allowed us to estimate eruption timescales for different active volcanoes, including the Phlegrean Fields, the island of Vulcano and Mt. Vesuvius volcano (Italy) and Sete Cidades Volcano (Sao Miguel island; Azores). We discovered that the time separating the starting of mixing at depth and eruptions was of the order of a few hours to minutes. These results have implications for civil protection planning of future volcanic crisis because these short timescales may imply little warning in volcanic crises. We anticipate our findings to be a reference point towards a unifying model explaining chemical exchanges in magmatic systems and supplying information on the use of chemical element mobility as geochronometers for volcanic eruptions. CHRONOS results provided unparalleled clues for building an inventory of past and recent volcanic eruption timescales and will be decisive for hazard assessment in active volcanic areas.