An integrated study of the driving forces and deposits of shallow water eruptions of volatile-rich basalt: Socorro 1993 revisited

浅水海底火山活动在海洋岛屿的形成中起着关键作用，并与人类种群和海洋生物群落的危害有关。其中一种最罕见的喷发方式是产生巨大的漂浮熔岩块，这些熔岩块充满了气体。当它们上升到海面时，这些“熔岩气球”通常会爆炸，然后沉降到海底。由于缺乏直接观察，人们对这种不寻常的海底火山活动知之甚少，只有5次这样的喷发被记录下来，所有这些喷发都发生在与火山热点相关的海洋岛屿上，如夏威夷、加那利群岛、亚速尔群岛和墨西哥的雷维拉吉多群岛。这项研究对这些漂浮的充满气体的熔岩块是如何在相对浅水的火山爆发中形成的有了更好的理解。该项目的重点是“熔岩气球”样本和其他相关的爆炸性火山产物，如火山灰和其他火山碎屑物质，这些物质是1993年从东太平洋墨西哥索科罗岛海岸的火山口喷发出来的。2017年，“鹦鹉螺号”（E/V Nautilus）进行海洋勘探时，一艘名为“大力神”（Hercules）的遥控潜水器在火山喷发区域收集了高分辨率视频，火山活跃时，在该区域观察到漂浮的充满气体的熔岩块。收集了其他火山物质和沉积物样品，并对其微量元素地球化学、挥发性含量、熔体包裹体以及由此产生的火山灰和喷出物层的沉积特征进行了分析。研究目标包括：(1)基于Hercules的超高分辨率测深测量，确定1993年Socorro火山口的形态、结构和性质；(2)对样品进行地球化学分析，表征样品的岩浆组成、挥发性含量和脱气历史、岩浆粘度和来源特征；(3)利用地球化学和结构分析输入的脱气模拟，建立了1993年事件的喷发模型。这项工作的更广泛影响包括研究生和本科生的学生培训，利用以高昂成本收集的独特样本，描述新指定的联合国教科文组织世界遗产，以及与海洋探索信托基金的互动，海洋探索信托基金有一个主要的公众和K-12外展计划，展示巡航和相关研究的科学成果。将制作一段广泛传播的视频，记录航海研究，向公众展示海洋地质学家在海上的生活，以及探索海底火山环境的奇观，并与墨西哥科学家进行国际合作。这项工作还将有助于火山活跃的海洋岛屿海岸周围的危害评估。从微米到米大小的火山喷出物，以及1993年墨西哥西海岸索科罗火山海底爆炸喷发产生的沉积物，将被地球化学和结构特征化，以确定喷发地点周围爆炸碎片的喷发和沉积条件。地球化学分析将包括矿物和玻璃分析，通过电子显微探针，新波213纳米激光烧蚀系统耦合到Thermo x系列II电感耦合质谱仪和Thermo Nicolet iS50傅里叶变换红外（FTIR）光谱仪。由此产生的微量元素数据将被建模，新的FTIR数据将提供Socorro岩浆喷发前气体含量的最小值。通过熔体夹杂物挥发性分析确定CO2/H2O脱气路径，将提供关于脱气是在封闭系统条件下还是在开放系统条件下发生的具体信息，并允许预测不同脱气方案下的囊泡性。岩浆上升速率将利用火山喷出物中的玻璃镶嵌物和斑晶中的挥发性扩散剖面来模拟。对于非常小的火山颗粒，将使用扫描电子显微镜（SEM）检查表面特征，以评估爆炸岩浆/海水相互作用在喷发过程中的作用。研究的另一个重要目标是为这种类型的浅水喷发建立一个约束良好的相模型（规模、形态、沉积类型），这些样品和这个遗址为古代、高度水泡的海底玄武岩序列的古环境解释提供了一个现代模拟。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。

Shallow water submarine volcanism plays a critical role in the formation of oceanic islands and is associated with hazards to both human populations and marine biological communities. One of the most rarely observed styles of these eruptions is the production of giant floating lava blocks that are filled with gas. When they rise to the sea surface these "lava balloons" often explode and then settle back down to the seafloor. Little is known about this unusual style of submarine volcanism due to the lack of direct observation as only five such eruptions have been documented, all of which occurred at oceanic islands associated with volcanic hotspots such as Hawaii, the Canary Islands, the Azores, and the Revillagigedo archipelago in Mexico. This research develops a better understanding of how these floating gas filled lava blocks are formed during relatively shallow water volcanic eruptions. The project focus on "lava balloon" samples and other associated explosive volcanic products, like ash and other pyroclastic material, erupted from vents off the shores of Mexico's Socorro Island in the eastern Pacific in 1993. During a 2017 oceanographic exploration by the ship, E/V Nautilus, high-resolution video was collected by a submersible, remotely-operated vehicle called Hercules in the area of the eruption at a location where floating gas filled lava blocks were observed while the volcano was active. Other samples of the volcanic material and deposits were also collected and their trace element geochemistry, volatile content, melt inclusions, and the depositional characteristics of the resulting volcanic ash and ejecta layers were targeted for analysis. Objectives of the research include (1) defining the morphology, structure, and nature of the 1993 Socorro vent site based on ultrahigh-resolution bathymetric surveys from the Hercules; (2) carrying out geochemical analyses on the samples to characterize their magmatic composition, volatile content and degassing history, their magma viscosity, and source characteristics; and (3) developing an eruption model for the 1993 event using degassing simulations with inputs from geochemical and textural analyses. Broader impacts of the work include student training at the graduate and undergraduate levels, leveraging unique samples collected at great cost, characterization of a newly designated UNESCO World Heritage Site, and interaction with the Ocean Exploration Trust which is has a major public and K-12 outreach program showcasing the cruise and science coming from the associated research. A video that will have wide dissemination, documenting seagoing research exposing the public to the life of a marine geologist at sea and the wonders of exploring submarine volcanic environments, will be created and there is international collaboration with scientists from Mexico. The work will also contribute to hazard evaluations around the coasts of volcanically-active oceanic islands.Volcanic ejecta of sizes from microns to meters and deposits of these that resulted from the 1993 explosive submarine eruption of Socorro Volcano off the western coast of Mexico will be characterized geochemically and texturally to determine the conditions of eruption and deposition of explosive debris around the vent site. Geochemical analyses will include mineral and glass analyses via electron microprobe, a New Wave 213 nanometer laser ablation system coupled to a Thermo X-Series II inductively coupled mass spectrometer, and a Thermo Nicolet iS50 Fourier Transform Infrared (FTIR) spectrometer. Resulting trace element data will be modeled and new FTIR data will provide minimum values of pre-eruption gas contents for the Socorro magma. CO2/H2O degassing paths, determined from melt inclusion volatile analyses, will provide specific information about whether degassing occurred under closed- or open-system conditions and allow predictions of vesicularities under different degassing scenarios to be made. Magma ascent rates will be modeled using volatile diffusion profiles in glass embayments and phenocrysts in the volcanic ejecta. For very small volcanic particles, a scanning electron microscope (SEM) will be used to examine surface features to evaluate the role of explosive magma/seawater interactions in the eruption process. Another important goal of the research will be development of a well-constrained facies model (scale, morphology, deposit types) for shallow water eruptions of this style, with these samples and this site providing a modern analogue for the paleo-environmental interpretation of ancient, highly vesicular submarine basaltic sequences.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.