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，但不可预见的火山爆发对世界各地的人类生命和财产构成了重大危害。除了对火山周围环境的直接威胁外，此类事件产生的火山灰云还会产生深远的影响，污染供水，使大片空域无法用于商业或国防交通。此外，即使是外国的火山也会危及美国人的生命，因为它们是受欢迎的旅游目的地。例如，2019年12月新西兰怀特岛（Whakaari）爆发，造成5名美国公民死亡，4人受伤。与近代史上许多致命的火山爆发一样，这次火山爆发是“潜水式”的，主要是由浅层过热蒸汽的爆炸性释放引起的，而不是由深层岩浆的直接作用引起的。这种喷发往往会突然发生；在许多情况下，当地监测网没有观察到任何明确或可靠的迹象表明爆炸即将发生。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火山喷发也会造成重大伤亡。该项目将以瓦卡里火山为例，结合复杂的计算机模拟和多年来的监测数据，跨越3次喷发，研究火山的长期演变。特别是，它试图研究Whakaari的非喷发活动是如何预先安排或为观测到的爆炸系统做好准备的。最终，这一过程将加深对一般的火山喷发的科学理解，而不仅仅是Whakaari火山，并将使这些不稳定的事件得到更可靠的预测，即使没有立即的警告信号。该项目的第一阶段将综合以往在数值模拟方面的进展，开发一种有限元模拟方法，能够全面捕捉火山浅层热液系统与周围宿主岩石之间的孔隙弹性相互作用。火山浅层热液系统是引发火山喷发的最常见因素。通过将流体流动的物理特性与岩石变形的物理特性相结合，该模型将能够预测火山如何对不同的渗透率和岩浆流入结构做出机械反应。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，找到与观测到的火山行为最匹配的潜在条件。然后，通过将这些模型的预测与额外的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，这个项目的目的是验证一个假设，即Whakaari火山爆发是由低渗透率热液密封的机械破裂引起的，这种密封在几个月到几年之前造成了压力的缓慢积累。此外，它还将确定系统的模拟应力状态是否足以单独导致密封失效，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这些事件是如何被触发的，在此之前可能发生什么前兆活动，以及为什么某些前兆可能出现在某些喷发中，而另一些则没有。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.