Collaborative Research: An Integrated Study of Silicic Lava Emplacement

了解熔岩流动的持续时间和速度是火山灾害管理和风险评估的核心。对基拉韦厄火山(夏威夷)和埃特纳火山(西西里)等持续喷发的火山进行了多年的观察，对玄武岩熔岩流动有了复杂的理解；然而，对其他类型的熔岩缺乏类似水平的理解。粘性的硅质熔岩喷发在地质记录中很常见，但在人类的时间尺度上很少见。因此，对活跃的硅质熔岩及其行为的观察非常有限。本世纪头十年，智利发生了两次特别粘稠的熔岩流纹岩喷发，首次对流纹岩熔岩喷发进行了实时观测。这些观察结果导致火山科学家需要重新检查硅质熔岩的流动方式，因为它们被认为比预期的流动速度更快，流动时间更长。在这项研究中，加利福尼亚州两个非常年轻的流纹岩熔岩流将成为详细研究的重点，在此研究中，将检查它们的内部和外部结构以及冷却历史，以便更好地了解它们是如何流动的，持续多长时间，速度有多快。这一结果将适用于未来加州东部、俄勒冈州、黄石国家公园和世界其他地方流纹岩熔岩的喷发。黑麻岩穹顶和南库利熔岩将成为外源和内源增长模式的焦点，使用结构建筑和应变、热和流变性梯度模式。研究人员将利用激光雷达数据编制详细的形态图，并利用田间宏观特征和微观应变研究进行三维结构分析。这些分析将表征和量化熔岩不同部分在喷发和侵位阶段活动的应变类型和程度。然后，应变数据集将与球晶和差示扫描量热仪的降温速度分析结果相结合，以限制侵位时间尺度。流变学实验将量化由于晶体、气泡和溶解水含量的变化而引起的有效粘度的变化。这些数据结合在一起，将产生一个全面的结构和热流变模型，描述硅质熔岩从喷发到停止，从喷口到边缘的演变过程。

Understanding the duration and speed of lava flows is central to volcanic hazard management and risk assessment. Years of observations at persistently erupting volcanoes like Kilauea (Hawaii) and Etna (Sicily) have produced a sophisticated understanding of basaltic lava flows; however, a similar level of understanding is absent for other types of lava. Eruptions of viscous, silicic lavas are common in the geological record but are infrequent at human timescales. Observations of active silicic lavas and their behavior are thus very limited. Two eruptions of a particularly viscous lava called rhyolite in the 2000s in Chile, allowed the first real-time observations of rhyolite lava eruptions. Those observations have led to the need for volcano scientists to re-examine the ways that silicic lavas flow because they were seen to be faster and flow for longer durations than anticipated. In this study, two very young rhyolite lava flows in California will be the focus of a detailed study in which their internal and external structures and cooling history will be examined in order to better understand how they flowed, for how long, and how fast. The results will be applicable to future eruptions of rhyolite lava in eastern California, Oregon, at Yellowstone National Park, and elsewhere around the world.Obsidian Dome and South Coulee lavas will be the focus for exogenous and endogenous growth patterns using structural architecture and strain, thermal, and rheological gradient patterns. The researchers will compile a detailed morphological map using LiDAR data and three-dimensional structural analyses using macroscopic features in the field and microscopic strain studies. The analyses will characterize and quantify the types and magnitudes of strain active in different parts of the lavas throughout stages of their eruption and emplacement. Strain datasets will then be integrated with the results of cooling rate analyses from spherulites and differential scanning calorimetry to constrain the emplacement timescales. Rheological experiments will quantify the variations in effective viscosity due to variations in crystal, bubble, and dissolved water contents. Together these data will produce a comprehensive structural and thermo-rheological model that describes the evolving flow of silicic lava from eruption to cessation, and from the vent to the margins.