Collaborative research: How variable is magma decompression rate during a single eruption?

了解控制火山喷发方式转变的过程是火山学中的主要悬而未决的问题之一，对减灾工作具有重要影响。协同作用的岩浆减压速率被认为是对火山喷发方式的主要控制，部分原因是它对气泡形成和迁移的动力学起到了调节作用。近年来，已经开发出利用快速熄灭的火山喷发中的化学梯度来限制岩浆减压速率的技术；然而，适用于应用这些技术的样本的稀缺性严重限制了可用于探索单一喷发过程中岩浆减压速率的时间变化的统计稳健数据集的获取。一种新开发的利用普遍存在的橄榄石晶体中的水浓度梯度的岩浆减压“时钟”现在可以用来克服这一限制。我们建议应用这个新的岩浆减压钟来研究加州拉森火山国家公园灰岩锥喷发的岩浆减压速率的时间变化。来自Cinder Cone的保存异常完好的Tephra序列捕捉到了从夏威夷式/斯特龙博利亚式到斯特龙博尔式/猛烈式的喷发风格的转变，为研究减压速率对喷发风格的控制作用提供了一个极好的天然实验室。拉森地区是美国最活跃的火山地区之一，对加州人、国家公园游客以及往返繁忙的旧金山湾区的航班构成重大危险。拟议工作的结果将与加州火山观测站、喀斯喀特火山观测站和拉森火山国家公园分享，这三个机构管理着加州的火山监测基础设施和火山灾害缓解工作。在拟议的工作中，将在1666年C.E.煤渣锥喷发矿床的协同温度变化和结构变化的背景下研究岩浆减压速率的变化。我们将使用三种独立的技术来估计岩浆减压速率：(1)橄榄石中水的扩散计时法；(2)气泡数密度；(3)微晶石数密度。此外，我们将使用橄榄石承载的熔体包裹体中的氧化镁分带来限制岩浆冷却速度。我们将建立一个统计稳健的减压速率和冷却速率估计的数据集，用于评估(首次在玄武岩系统中)在喷发风格的转变过程中，减压速率和冷却速率在时间上的变化。这种方法将使我们能够对即将喷发的管道中压力-温度-时间条件的演变进行前所未有的详细研究，从而增加我们对玄武岩火山喷发爆炸性控制的理解。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。

Understanding the processes that govern transitions in volcanic eruptive style is one of the major outstanding questions in volcanology, with important implications for hazard mitigation efforts. Syneruptive magma decompression rate is thought to be a dominant control on volcanic eruptive style, due in part to its role in modulating the dynamics of bubble formation and migration. In recent years, techniques have been developed that use chemical gradients in rapidly quenched volcanic tephra to constrain magma decompression rates; however, the rarity of suitable samples for the application of these techniques has severely limited the acquisition of statistically robust datasets that could be used to explore temporal variations in magma decompression rate over the course of a single eruption. A newly developed magma decompression “clock” that exploits water concentration gradients in prevalent olivine crystals can now be used to overcome this limitation. We propose to apply this new magma decompression clock to study temporal variations in the decompression rate of magma erupted at Cinder Cone, Lassen Volcanic National Park, CA. The exceptionally well-preserved tephra sequence from Cinder Cone captures a transition in eruptive style from Hawaiian/Strombolian to Strombolian/Violent Strombolian, providing an excellent natural laboratory for studying the role of decompression rate as a control on eruptive style. The Lassen region is one of the most active volcanic regions in the US and poses a significant hazard to Californians, National Park visitors, and flights to and from the busy San Francisco Bay Area. The results of the proposed work will be shared with the California Volcano Observatory, the Cascade Volcano Observatory, and Lassen Volcanic National Park, which manage volcano-monitoring infrastructure and volcanic hazard mitigation efforts in California.In the proposed work, variations in magma decompression rate will be studied in the context of syneruptive temperature changes and textural variations in the 1666 C.E. Cinder Cone eruptive deposit. We will apply three independent techniques to estimate magma decompression rates: (1) water-in-olivine diffusion chronometry; (2) bubble number density; and (3) microlite number density. Additionally, we will constrain magma cooling rates using MgO zonation in olivine-hosted melt inclusions. We will build a statistically robust dataset of decompression rate and cooling rate estimates that will be used to assess (for the first time in a basaltic system) temporally resolved variations in decompression rate and cooling rate across a transition in eruptive style. This approach will allow the evolution of pressure-temperature- time conditions in the conduit just prior to eruption to be studied in unprecedented detail, thereby increasing our understanding of the controls on the explosivity of basaltic volcanic 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.