Controls on explosive basaltic eruptions within the San Francisco Volcanic Field: Constraints from seismic imaging and multiphase magma ascent modeling

对旧金山火山场内爆炸性玄武岩喷发的控制：地震成像和多相岩浆上升模型的限制

• 批准号: 2202666
• 负责人: Eric Kiser
• 金额: $ 74.91万
• 依托单位: University of Arizona
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-09-01 至 2025-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2202666&HistoricalAwards=false
• 关键词: Controls; explosive; basaltic; eruptions; within

Volcanic eruptions are major hazards that can cause significant socio-economic effects on local populations and short-term changes to the climate that have a global impact. Many eruptions are fed by a single conduit that brings magma to the surface repeatedly over time producing major volcanic edifices associated with volcanic arcs around the world. In contrast, volcanic fields are composed of tens to hundreds of volcanic vents that are distributed over areas of 100 to 100,000 km2. These vents typically only produce a single eruption before becoming inactive and the locations of subsequent eruptions can be unpredictable and at significant distances from the previous events. Furthermore, the eruption styles within these volcanic fields can vary between non-explosive lava flows to violently explosive events that eject volcanic ash and gases tens of kilometers into the atmosphere. The San Francisco Volcanic Field (SFVF) in Northern Arizona exhibits these classic characteristics of a volcanic field and includes one of the best documented examples of an explosive eruption within these settings at Sunset Crater northeast of Flagstaff, AZ. The distribution of volcanic vents in the SFVF and why significant variability exists in the eruption styles of the volcanic field remain poorly understood. This is not only the case for the SFVF, but for every volcanic field on Earth, making it difficult to understand potential hazards these systems represent to local populations. This project seeks to better understand this system by combining seismological and eruption modeling approaches. Hundreds of instruments used for measuring ground motion (seismometers) will be installed throughout the SFVF in order to detect signals from local earthquakes. This seismological component of the project will be complemented by the development of computer models that simulate volcanic eruptions. In addition to exploring the general conditions necessary for producing non-explosive and explosive eruptions in volcanic fields, this component of the project will use the details of magma distribution beneath Sunset Crater derived from the seismological work, to constrain the specific conditions that led to this eruption. This will be the first project of its kind to produce a detailed image of the magmatic system beneath an entire volcanic field and directly use these constraints to improve eruption modeling. The work will improve hazard assessment for local populations (e.g., Flagstaff, AZ), as well as for population centers near other volcanic fields around the world (e.g., Auckland, New Zealand). Students from Chandler-Gilbert Community College in Arizona will participate in the research for this project and will be recruited to come to the University of Arizona following completion of their 2-year degrees. Teaching modules related to volcanic hazards will also be produced from this project and distributed to the broader academic community.The San Francisco Volcanic Field (SFVF) covers an area approximately 5,000 km2 in northern Arizona and includes nearly 600 basaltic vents interspersed with a few, large-volume intermediate to silicic volcanic centers. Over the past ~5-6 Myr, the locus of volcanism at the SFVF has migrated eastward at a rate of 1-3 cm/yr with the 1085 CE eruption that produced Sunset Crater being the youngest in this volcanic field. Though most of the volcanic vents within the SFVF exhibit landforms common to the effusive eruption styles of distributed volcanic fields, the Sunset Crater eruption was violently explosive and significantly affected the indigenous population living in the region at the time. Key to improving our understanding of the hazards of the SFVF is better constraining the conditions that led to the sub-Plinian style eruption at Sunset Crater which did not affect nearby volcanic vents. Existing studies have indicated that a mid-crustal magma storage zone played a key role in the Sunset Crater eruption, however, currently our understanding is limited regarding how the properties of this storage zone (e.g., size, depth, melt fraction, volatile content) influenced the eruption. Details of the crustal magma storage system that have resulted in differing volcanic compositions (mafic vs. felsic) within the SFVF are also unknown. By integrating seismic imaging and eruption modeling, this project lays out a holistic approach to better understand the subsurface magmatic plumbing system and processes that drive volcanic activity within the SFVF. Specific components of this project will include (1) detailed characterization of seismicity and the development of high-resolution 3D seismic velocity models of the crust beneath the SFVF to image current and past magmatic systems associated with this volcanic field, (2) the development of coupled magma chamber pressurization and multiphase magma ascent models to determine the conditions necessary to drive effusive to explosive basaltic eruption styles, and (3) combining constraints from seismic imaging work on the volumes and depths of crustal magma reservoirs with these state-of-the-art eruption models to better understand the subsurface processes that drove the violently explosive Sunset Crater eruption.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.

火山爆发是重大灾害，可对当地人口造成重大的社会经济影响，并对具有全球影响的气候造成短期变化。许多火山爆发都是由一个单一的管道提供的，随着时间的推移，岩浆不断地上升到地表，产生了与世界各地的火山弧相关的主要火山大厦。相比之下，火山场由数十到数百个火山口组成，分布在100至100,000平方公里的面积上。这些喷口在变得不活跃之前通常只会产生一次喷发，随后的喷发地点可能是不可预测的，并且与之前的事件距离很远。此外，这些火山区域内的喷发方式也各不相同，既有非爆炸性的熔岩流，也有将火山灰和气体喷射到数十公里外的大气中的剧烈爆炸事件。亚利桑那州北部的旧金山火山场（SFVF）展示了火山场的这些经典特征，其中包括在亚利桑那州弗拉格斯塔夫东北部日落火山口的这些环境中爆发的最佳记录之一。SFVF火山口的火山口分布以及火山场喷发风格存在显著变化的原因仍然知之甚少。这不仅是SFVF的情况，而且是地球上每一个火山场的情况，这使得很难理解这些系统对当地居民的潜在危害。这个项目试图通过结合地震学和火山喷发建模方法来更好地理解这个系统。数百个测量地面运动的仪器（地震仪）将被安装在整个SFVF，以探测本地地震的信号。该项目的地震学部分将由模拟火山喷发的计算机模型的发展加以补充。除了探索在火山领域产生非爆炸性和爆炸性喷发所需的一般条件外，该项目的这一部分将使用地震学工作得出的日落火山口下岩浆分布的细节，来限制导致这次喷发的具体条件。这将是同类项目中第一个生成整个火山场下岩浆系统的详细图像，并直接使用这些约束条件来改进火山喷发模型。这项工作将改进对当地居民（例如，亚利桑那州弗拉格斯塔夫）以及世界上其他火山场附近的人口中心（例如，新西兰奥克兰）的危害评估。来自亚利桑那州钱德勒-吉尔伯特社区学院的学生将参与该项目的研究，并将在完成两年制学位后被招募到亚利桑那大学。该项目还将制作与火山灾害有关的教学模块，并分发给更广泛的学术界。旧金山火山场（SFVF）位于亚利桑那州北部，占地面积约5000平方公里，包括近600个玄武岩喷口，散布着一些大体积的中硅酸火山中心。在过去的5-6 Myr里，SFVF的火山活动中心以1-3 cm/年的速度向东迁移，其中1085年产生的日落火山口是该火山区最年轻的火山。虽然SFVF内的大部分火山口呈现出与分布式火山场的喷涌喷发样式相同的地貌，但Sunset Crater的喷发是剧烈的，并对当时居住在该地区的土著居民产生了重大影响。提高我们对SFVF危害认识的关键是更好地约束导致日落火山口亚普林尼式喷发的条件，而不影响附近的火山口。已有研究表明，中地壳岩浆储存带在Sunset Crater喷发中发挥了关键作用，然而，目前我们对该储存带的性质（如大小、深度、熔体分数、挥发物含量）如何影响喷发的了解有限。导致SFVF内不同火山成分（基性与长英质）的地壳岩浆储存系统的细节也未知。通过整合地震成像和火山喷发模型，该项目提出了一种全面的方法，以更好地了解地下岩浆管道系统和驱动SFVF内火山活动的过程。该项目的具体组成部分将包括：(1)详细描述地震活动性和开发SFVF下地壳的高分辨率3D地震速度模型，以成像与该火山场相关的当前和过去的岩浆系统；(2)开发耦合岩浆室加压和多相岩浆上升模型，以确定驱动溢流到爆炸性玄武岩喷发风格所需的条件。(3)将地震成像工作对地壳岩浆储层体积和深度的限制与这些最先进的喷发模型相结合，以更好地了解驱动剧烈爆炸的日落火山口喷发的地下过程。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。