Volatile resorption expedites eruption onset in large silicic systems

Silicic caldera-forming eruptions are among the most hazardous natural phenomena on Earth, yet their triggering mechanisms remain poorly understood. While volatile exsolution is often recognized as a key eruption driver in large silicic systems, we show that volatile resorption can, counterintuitively, promote chamber pressurization and expedite eruption onset. Using a thermo-mechanical magma chamber model, we investigate the conditions that facilitate resorption and its impacts on reservoir stability and eruption timing. Resorption occurs in rapidly recharged systems driven by pressure increase and dilution of the resident melt. Independent apatite data from the Aso-4 eruption (~86 kyrs, Japan) tracks pre-eruptive loss of volatiles supporting the natural occurrence of volatile resorption. Aso-4 offers a case study where complete volatile dissolution to undersaturation is modelled if the resident magma contained 4-4.5 wt% H ₂ O and ~100 ppm CO ₂ , consistent with petrologic data, and is recharged with drier, hotter magmas at rates >10 ^-2.4 km ³ /yr. Through a reduction in bulk magma compressibility, resorption amplifies chamber pressurization and expedites eruption onset, which could have triggered Aso-4 up to 100 years earlier than in scenarios that retain exsolved volatiles. We propose that volatile resorption promotes rapid chamber pressurization, and detecting its signatures could provide early warning of imminent eruption.