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

了解火山喷发方式转变的过程是火山学中的一个主要突出问题，对减灾工作具有重要意义。协同岩浆减压速率被认为是火山喷发方式的主要控制因素，部分原因是它在调节气泡形成和迁移动力学方面的作用。近年来，已经开发出的技术，使用化学梯度在快速淬火火山熔岩约束岩浆减压速率，然而，适用于这些技术的应用样本的稀缺性，严重限制了收购的统计稳健的数据集，可用于探索时间变化的岩浆减压速率在一个单一的喷发过程中。一个新开发的岩浆减压“时钟”，利用水的浓度梯度在流行的橄榄石晶体，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时钟研究火山灰锥，拉森火山国家公园，加利福尼亚州的岩浆喷发减压率的时间变化。Cinder Cone中保存完好的火山灰序列捕捉到了从Hawaiian/Strombolian到Strombolian/Violent Strombolian的喷发风格的转变，为研究减压率作为喷发风格控制因素的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忙碌的弗朗西斯科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共享，这些机构负责管理加州的火山监测基础设施和火山灾害缓解工作。在拟议工作中，将在1666年同喷发温度变化和纹理变化的背景下研究岩浆减压速率的变化。火山灰锥喷发存款。我们将应用三种独立的技术来估计岩浆减压速率：（1）橄榄石中水扩散计时法;（2）气泡数密度;（3）微晶数密度。此外，我们将限制岩浆冷却速率使用MgO分带橄榄石托管熔融包裹体。我们将建立一个统计上可靠的减压速率和冷却速率估计数据集，用于评估（首次在玄武岩系统中）在喷发风格过渡期间减压速率和冷却速率的时间分辨变化。这种方法将允许在火山爆发前的管道中的压力-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爆发爆炸性控制的理解。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

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.