Constraining the mechanisms and timing of magma ascent in plinian eruption through decompression experiments: a case study from the Pomici di Base eruption, Mt. Somma-Vesuvius (Naples, Italy)

全世界约有8亿人生活在活火山周围100公里以内。正如2010年埃亚菲尔火山(冰岛)喷发产生的火山灰排放所表明的那样，火山喷发不仅会造成生命和生计损失，造成社会混乱，而且还会对关键基础设施造成破坏，从而引发全球经济危机。坎帕尼亚火山区(意大利那不勒斯)有多达300万居民，是世界上最危险的火山区之一，因此受到了深入的研究和监测。尽管如此，仍然无法预测前兆活动，如火山气体的变化、地面变形或地震活动，是否会导致低强度或灾难性的喷发。与火山管道中的岩浆上升有关的排气过程是关键问题，因为它们控制着火山喷发的类型和强度。事实上，爆炸性喷发是由挥发性成分释放到单独的流体相驱动的。这一过程通常是由于岩浆上升进入管道后或包围岩浆室的岩石破裂后压力下降所致。然而，岩浆减压和泡囊作用之间的关系仍然没有得到很好的研究和了解。在本研究中，我们计划在高压高温装置上对波米奇迪基地喷发(那不勒斯索玛-维苏威乌斯山)沉积下来的富含H2O-CO2的宽质和碎屑质熔体进行减压实验。我们的目的是了解具有高到中等粘度的成因相关的岩浆在岩浆隆起过程中如何在泡泡和气泡生长方面表现出来。此外，我们的目标是推动快速减压实验，接近或直接导致岩浆破碎。系统地改变气泡的挥发性成分、含量和减压速率，有助于更好地表征气泡的气泡形成和生长机制(S)和速率(S)之间的关系，以及破碎深度与喷发方式的关系。所获得的结果将有助于解释自然系统中导致这些系统向明显异常喷发行为转变的晚期广泛的岩浆泡沫化。它们还将提供关键数据，以模拟岩浆上升过程中的脱气过程，了解喷发风格的演变，并计算不稳定的预算。

Worldwide about 800 million people live within 100 km of active volcanoes. As the ash emissions from the 2010 eruption of Eyjafjöll (Iceland) showed, volcanic eruptions can cause not only societal disruption trough the loss of life and livelihoods, but also a global economic crisis trough damage of critical infrastructure. The Campanian Volcanic District (Naples, Italy), counting up to 3 million inhabitants, is among the most dangerous volcanic areas worldwide and therefore deeply studied and monitored. Despite this, it is still impossible to predict if precursor activity, such as changes in volcanic gases, ground deformation or seismicity, may lead to low intensity or to catastrophic eruptions.Degassing processes related to magma rise in volcanic conduits are crucial issues as they control the style and intensity of volcanic eruptions. In fact, explosive eruptions are driven by the exsolution of volatile components to a separate fluid phase. This process is commonly caused by decreasing pressure after magma ascent into the conduit or after failure of rocks enclosing the magma chamber. However, the relations between magma decompression and vesiculation are still poorly investigated and understood.In this study, we plan to perform decompression experiments in high-pressure high-temperature apparatus on H2O-CO2 bearing latitic and trachitic melts from the plinian fallout of the Pomici di Base eruption (Mt.Somma-Vesuvius, Naples). Our aim is to understand how genetically related magmas with high to intermediate viscosity behave during magma uprising in terms of vesiculation and bubble growth. Furthermore, we aim to drive fast decompression experiments leading close to, or directly to magma fragmentation. Systematically changing the volatile compositions and contents and the decompression rates, this research will help to better characterize the relationship between the mechanism(s) and rate(s) of bubble vesiculation and growth, the fragmentation depth and the eruptive style. The obtained results will be useful to interpret late-stage, extensive magma vesiculation in natural systems leading to a shift of those systems towards apparently anomalous eruptive behavior. They will also provide key data to model degassing processes during magma ascent, to understand the evolution of eruptive style and to work out the volatile budget.