Investigating cyclic changes in the potential field at Soufrière Hills volcano, Montserrat

火山爆发是自然界最壮观的事件之一，但对数百万人的生命和财产构成威胁。火山爆发是复杂的地下过程的结果，这导致地球物理监测记录的可量化信号。岩浆迁移、构造和热液活动等过程可以引发地震活动、地面变形、热变化以及火山周围磁场和重力场的变化。地球物理记录显示，火山活动经常遵循循环模式。火山科学家面临的挑战在于破译地球物理信号及其循环行为的原因。通常，火山喷发的信号几乎完全归因于岩浆作用。然而，人们越来越认识到，水文储层（如地下水流动和补给）和热液储层（如蒸汽/液体界面传播）中的浅层过程对地表记录的地球物理信号有重要影响和诱发作用。基于PI在侦察研究期间获得的循环数据，该项目旨在通过对Montserrat (B.W.I) soufri<e:1>活火山的地球物理信号进行新颖的多参数调查来解决这一挑战。该项目建议通过结合连续地面变形和连续势场（重力和电磁）研究来调查火山的地下系统。全球定位卫星系统（GPS）可以量化火山下体积变化引起的地面变形，精确到亚厘米。重力仪能够分辨出地球引力场中由于质量放置或深度密度变化而产生的微小变化（1 / 10^8）。甚低频电磁测量记录了深度小于500米的地面物理化学变化期间的电导率对比。这三种技术的结合可以直接量化浅层过程及其对火山现有监测网记录的其他地球物理信号的影响。结合这两种技术可以量化体积和质量随时间的变化，从而推断出浅层诱发源的密度。热液流体的密度与自来水相似或更低。火山喷发的岩浆密度至少是原来的两倍。该项目的目的是：1)通过连续势场和地面变形测量，量化特别是与SHV浅层次地表过程有关的短期循环活动；2)开发浅层过程的概念物理模型；3)分离水文和热液过程对记录信号的贡献，并获得对其动力学的基本理解。iv)将浅层信号与火山喷发信号相关联，以探索火山喷发时深层和浅层过程的相互作用；v)设计将势场测量整合到SHV现有监测计划中的策略；vi)提供关于蒙特塞拉特南部地热开发前景的第一次热液动力学量化。结果将与蒙特塞拉特火山观测站工作人员进行的补充地球物理和地球化学调查的数据一起进行验证和解释，以确定和分离与（浅）热液和（深）岩浆活动有关的动力学，以改进对火山活动的预测

Volcanic eruptions are among the most spectacular events of the natural world, but pose a threat to lives and property of millions of people. Eruptions are the effect of complex sub-surface processes, which lead to quantifiable signals recorded by geophysical monitoring. Processes such as magma migration, tectonic and hydrothermal activity can trigger seismicity, ground deformation, thermal variations and changes in the magnetic and gravity fields around a volcano. Very often volcanic activity follows cyclic patterns, revealed by the geophysical record. The challenge for volcano scientists lies in deciphering causes for the geophysical signals and for their cyclic behaviour. Usually, signals at an erupting volcano are almost exclusively attributed to magmatic processes. However, there is a growing awareness that shallow processes in hydrological reservoirs (e.g., ground water flow and recharge) and hydrothermal reservoirs (e.g., steam/liquid interface propagation) have an important influence on and induce geophysical signals recorded at the ground surface. Based on cyclic data obtained by the PI during a reconnaissance study, this project aims to tackle this challenge via a novel multi-parametric investigation of geophysical signals at the active Soufrière Hills volcano, Montserrat (B.W.I). The project proposes to investigate the sub-surface system at the volcano via a combination of continuous ground deformation and continuous potential field (gravimetric and electromagnetic) studies. Global Positioning Satellite Systems (GPS) can quantify ground deformation caused by volume changes beneath a volcano to sub-centimetre precision. Gravimeters are capable of resolving minute changes (1 in 10^8) in the Earth's gravitational field due to mass emplacement or density changes at depth. Very low frequency electromagnetic measurements record electrical conductivity contrasts during physico-chemical changes in the ground at less than 500 m depth. The combination of the three techniques enables the direct quantification of shallow processes and their influence on other geophysical signal recorded in the existing monitoring network at the volcano. Combining the techniques enables the quantification of volume and mass changes over time, from which to infer the density of the causative source at shallow depth. Hydrothermal fluids have densities similar or lower than that of tap water. Magma erupted at the volcano is by at least a factor of two denser. The project aims to i) quantify short-term cyclic activity particularly related to shallow sub-surface processes at the SHV via continuous potential field and ground deformation measurements, ii) develop conceptual physical models of shallow processes, iii) separate contributions from hydrological and hydrothermal processes to the recorded signals and to obtain a fundamental understanding of their dynamics, iv) to correlate shallow signals with eruption signals to explore the mutual interaction of deep and shallow processes at an erupting volcano, v) devise strategies for integrating potential field measurements into existing monitoring programs at SHV and vi) to provide a first quantification of hydrothermal dynamics with respect to the prospect of geothermal exploitation in the south of Montserrat. Results will be validated and interpreted together with data from supplementary geophysical and geochemical investigations performed by staff of the Montserrat volcano observatory to identify and separate dynamics pertaining to (shallow) hydrothermal and (deep) magmatic activity for improved forecasting volcanic activity