Scanning micro-XRF: the “rapid blood test” approach to volcanic eruption monitoring

A comprehensive time-series of integrated chemical and textural data from products of the 2021 eruption on La Palma, Canary Islands, using scanning micro-XRF are presented. Within our data we observe critical changes in plumbing system dynamics, including a progressive shutting-down of deep magma supply, weeks before the eruption concluded. These data and our workflow demonstrate how near-real-time volcano petrology can now be delivered. Answering “what is happening now?” has long been the highest priority for volcanic observatories, and approaches with rapid and data-rich returns like geophysics, and less so gas geochemistry, are favoured. This is like listening to the heartbeat or smelling the breath of volcanoes respectively, which can indicate changes are occurring deep within the plumbing system. Yet with approximately 20% of the world’s increasing and interconnected population now living within a 100 km of an active volcano, answers to new questions are being urgently demanded. To understand the driving mechanisms of melting, storage, crystalisation, volatile charging, ascent, and eruption of magma, comprehensive “blood tests” are needed which can help answer “what will happen next?” and “how long will it continue?”. This is shown to be possible with scanning micro-XRF. Moreover, geophysics and gas geochemistry cannot be used to look back into the past of a volcano, and so are faced with an unaddressable lack of empirical historical comparisons. Our study disproves the traditional view that petrology is too slow, too expensive, and too specialized to deploy in many volcano monitoring settings.