Collaborative Research: Exploring the Magmatic, Crustal, and Conduit Conditions Required for Mafic, Plinian Volcanism

低硅“镁铁质”岩浆是地球上最常见的喷发岩浆。由于它们的粘度很低，它们通常形成熔岩流或微弱的爆炸性喷发。然而，镁铁质成分的火山可以产生强度更大的普林尼安式喷发，能够将火山灰散落在数千平方公里的土地上，并产生致命的、改变地貌的火山灰流，从源头流经数十公里。尽管它们可能产生影响，但导致普林尼安镁铁质火山喷发的机制尚不清楚。该项目将通过限制此类喷发的原因和后果而使社会受益，这对生活在镁铁质火山中心(包括美国目前活跃的基拉韦厄火山)的数百万人具有全球影响。博伊西州立大学(BSU)的两名博士生将由团队中的五名参与科学家进行培训，在促进教学、培训和学习的同时促进发现和理解。来自智利康塞普西翁大学的本科生将参加实地工作和研究，扩大任职人数不足群体的参与。研究团队的成果和经验将通过我们实地工作的一系列博客文章和短视频在北卡罗来纳州立大学岩浆和火山研究小组Facebook页面上分享，记录与该项目相关的发现的关键要素。最后，调查人员和学生将把智利工作的样本、故事、图像和视频纳入当地和地区的推广工作。该项目的目标是智利Volcan Llaima的13.4ka(~12 km3 Dre)和~12.6ka(1 Km3 Dre)镁铁质喷发，这些喷发在火山周围产生了广泛的火山灰流沉积。喷发规模的不同使得研究促进大体积破火山口形成镁铁质火山喷发与小体积普林尼安镁铁质火山喷发的过程成为可能。一整套多样但免费的方法，包括岩石学、地球化学、物理火山学、减压实验和流变学实验，使研究团队能够解决广泛的基本研究问题，即什么岩浆和地壳条件促进和触发基性普林尼安火山喷发。更具体地说，空间和地层受限的岩石学和地球化学研究将使我们能够调查喷发期间和喷发前的岩浆条件，如岩浆成分的变异性以及洞室温度、压力和气体含量的变化。在这些条件下确定可变性将允许重建岩浆管道系统。所有方法的组合被用来限制促进镁铁质熔体高爆炸性的管道条件，包括岩浆上升速度和脱气之间的相互作用，以及防止气体损失的岩浆流变学变化，从而促进更高的爆炸性。这项工作的结果将对理解延伸到世界各地镁铁质中心的爆炸性镁铁质喷发过程产生影响，包括大体积和小体积镁铁质、普林尼安火山喷发。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。

Low-silica 'mafic' magmas are the most common magmas to erupt on Earth. Because their viscosity is low, they usually form lava flows or weak explosive eruptions. However, mafic-composition volcanoes can produce much stronger, Plinian-style eruptions capable of dispersing ash fall over thousands of square kilometers, and producing deadly, landscape-altering ash flows that travel tens of kilometers from source. Despite their potential impact, the mechanisms responsible for generating mafic, Plinian eruptions are not understood. This project will benefit society by constraining the causes and consequences of such eruptions, which has global implications for the millions of people living at risk from mafic volcanic centers including the currently active Kilauea volcano in the USA. Two Boise State University (BSU) PhD students will be trained by the five participating scientists on the team, advancing discovery and understanding while promoting teaching, training, and learning. Undergraduate geoscience students from the Universidad de Concepcion (Chile) will be included in the field work and research, broadening participation of under-represented groups. The results and experience of the research team will be shared on the BSU magmatic and volcanic studies group Facebook page through a series of blog post and short videos of our field work that document the key elements of discovery associated with the project. Finally, the investigators and students will incorporate samples, stories, images and videos from the work in Chile into local and regional outreach efforts.This project targets the 13.4_ka (~12 km3 DRE) and ~12.6 ka (1 km3 DRE) mafic eruptions at Volcan Llaima, Chile, which produced extensive ash flow deposits found radially around the volcano. The difference in eruption sizes permits investigation of processes that promote large-volume, caldera forming mafic eruptions versus smaller volume Plinian mafic eruptions. A full suite of diverse but complimentary methods, including petrology, geochemistry, physical volcanology, decompression experiments, and rheology experiments, allows the research team to address the broad, fundamental research question of what magmatic and crustal conditions promote and trigger mafic, Plinian eruptions. More specifically, spatially and stratigraphically constrained petrologic and geochemical studies will allow us to investigate magmatic conditions during and prior to eruption, such as compositional variability of the magma and changes in chamber temperatures, pressures, and gas content. Establishing variability in these conditions will permit reconstruction of the magma plumbing system. A combination of all methods are used to constrain conduit conditions that promote high explosivity for mafic melts, including the interplay between ascent rate and degassing of the magma, as well as changes in magma rheology that prevent gas loss, promoting higher explosivity. The results of this work will have implications for understanding explosive mafic eruptive processes that extend to mafic centers worldwide, including both large-volume and small-volume mafic, Plinian eruptions.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.