EAR-PF: Short fuses: investigating recent phreatic eruptions at Whakaari, New Zealand, through poroelastic modeling

尽管最近在火山监测方面取得了许多进展，但不可预见的火山喷发对世界各地的人类生命和财产构成了重大威胁。除了对火山周围环境的直接威胁外，这类事件产生的火山灰云可能会产生深远的后果，污染供水，使商业或国防交通无法使用大片空域。此外，鉴于外国火山作为旅游目的地的受欢迎程度，即使是外国火山也可能危及美国人的生命。例如，2019年12月新西兰怀特岛(Whakaari)火山喷发造成5名美国公民死亡，4人受伤。与近代史上的许多致命喷发一样，这次喷发是“潜水”的，主要是由浅层过热蒸汽的爆炸性释放驱动的，而不是由深层岩浆的直接作用驱动的。这种喷发往往是突然发生的；在许多情况下，地方监测网络没有观察到任何明确或可靠的迹象，表明即将发生爆炸。在这些情况下，地方当局无法疏散该地区，导致即使是相对较小的喷发也造成了重大伤亡。以Whakaari为例，该项目将把复杂的计算机模拟与跨越3次喷发的多年监测数据结合起来，以调查火山的长期演化。特别是，它试图研究Whakaari的非喷发活动可能是如何为观测到的爆炸预置或启动系统的。最终，这一过程将加深对总体上潜水喷发的科学理解，不仅限于Whakaari，而且将使这些不稳定的事件能够更可靠地预测，即使在没有即时警告信号的情况下也是如此。该项目的第一阶段将综合以前在数值模拟方面的进展，以开发能够完全捕捉火山浅层热液系统与周围围岩之间的孔弹性相互作用的有限元模拟。通过将流体流动物理和岩石变形物理相结合，该模型将能够预测火山将如何对不同渗透率和岩浆流入的不同配置做出机械反应。研究的第二阶段将使用统计数据同化技术，将这些预测与Whakaari的地面变形测量结果进行比较，找到与火山观测到的行为最匹配的一组潜在条件。然后，通过将这些模型的预测与其他地震和地球化学观测结果进行比较，可以进一步约束和验证这些模型。最后，该项目旨在验证这样一种假设，即Whakaari火山喷发是由于低渗透性热液封层的机械破裂造成的，在此之前的几个月到几年里，压力一直在缓慢积累。此外，它将确定系统的模拟应力状态是否足以单独导致密封故障，或者是否需要额外的外部触发。通过在火山系统长期机械演化的背景下考虑潜水喷发，这项研究将有助于理解如何触发事件，可能预先发生什么前兆活动，以及为什么某些前兆可能存在于一些喷发而不是另一些喷发。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Despite many recent advances in volcano monitoring, unforeseen volcanic eruptions pose a major hazard to human life and property around the world. Beyond the direct threat to the volcano’s immediate surroundings, ash clouds from such events can have far-reaching consequences, contaminating water supplies and rendering large sections of airspace unusable to commercial or defense traffic. Moreover, even foreign volcanoes can endanger American lives, given their popularity as tourist destinations. For example, the December 2019 eruption of Whakaari (White Island) in New Zealand left 5 American citizens dead and wounded 4 others. As with many deadly eruptions in recent history, this event was “phreatic”, driven primarily by the explosive release of shallow superheated steam rather than by the direct action of deeper magma. Such eruptions tend to occur suddenly; in many cases local monitoring networks do not observe any clear or reliable indication that an explosion is imminent. In these scenarios, local authorities are unable to evacuate the area, leading to significant casualties even from relatively small eruptions. Using Whakaari as a case study, this project will combine sophisticated computer simulations with years of monitoring data, spanning 3 eruptions, to investigate the volcano’s longer-term evolution. In particular, it seeks to study how non-eruptive activity at Whakaari may have predisposed or primed the system for the observed explosions. Ultimately, this process will deepen the scientific understanding of phreatic eruptions in general, beyond just Whakaari, and will allow these volatile events to be forecasted more reliably, even in the absence of immediate warning signs.The first stage of this project will synthesize previous advances in numerical modeling to develop a finite element simulation capable of fully capturing the poroelastic interactions between a volcano’s shallow hydrothermal system, from which phreatic eruptions are most often triggered, and the surrounding host rock. By combining the physics of fluid flow with those of rock deformation, this model will be able to predict how the volcano would mechanically respond to different configurations of permeability and magma influx. The second phase of the study would then use statistical data assimilation techniques to compare these predictions against measurements of ground deformation at Whakaari, finding the sets of underlying conditions that best match the volcano’s observed behavior. These models can then be further constrained and validated by comparing their predictions against additional seismic and geochemical observations. In the end, this project aims to test the hypothesis that Whakaari’s eruptions were caused by the mechanical rupture of low-permeability hydrothermal seals which had caused the slow accumulation of pressure in the months to years beforehand. Additionally, it will determine whether the modeled stress state of the system would have been sufficient to cause seal failure alone, or if an additional external trigger was required. By considering phreatic eruptions in the context of a volcanic system’s longer-term mechanical evolution, this study will help to understand how there events are triggered, what precursory activity may occur beforehand, and why certain precursors may be present for some eruptions but not others.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.