Infrared Spectroscopy of Silicic Glasses and Melts: Deriving Volcano-Scale Processes from Laboratory-Scale Measurements

活火山通常会产生危险的圆顶和流动，这些圆顶和流动要么是富含气体的熔岩，含有一系列气泡和玻璃成分，要么是密集的碎石堆和块，就像正在喷发的Mt。圣海伦火山。 前一种形式可以在圆顶挤压和危险的爆炸喷发之间交替。 后一种类型通常危险性较小，但如果足够大，仍然可以灾难性地坍塌，形成致命的块和火山灰流。 为了评估与活动熔岩圆顶相关的危险，需要许多信息，包括圆顶的类型/成分/温度。 然而，直接收集手样本通常风险太大（就像在Mt. 2004年圣海伦火山爆发）。 监测活动熔岩穹丘成分和温度的远程技术是更可取的，最适合这些测量的数据是在热红外（TIR）波长区域。 TIR数据可以从空间或现场仪器收集，这些仪器位于远离活动喷口的安全位置（几公里）。 TIR波长对这些圆顶的发射热量和矿物成分都很敏感。 然而，为了定量地了解来自天然熔岩圆顶的TIR信号，需要关键的实验室数据。 研究人员建议在实验室中使用根据先前资助开发的微型熔炉收集天然玻璃和熔融材料的数据，以便通过调整热摄像机（FLIR）来捕获多光谱数据，将这项研究扩展到该领域，这将模拟从太空收集的数据。 提出的研究具有重要的理论意义的TIR光谱/遥感数据分析以及火山灾害监测/缓解的实际应用。 实验室的结果将与实地和卫星TIR数据进行比较，并将提供有助于开发下一代实地监测工具的信息。 该项目将支持富有成效的国际合作，并资助博士学位-具体而言，建议进行后续研究，包括实验室和现场任务，以表征基本Si-（Al）-O单元振动产生的硅酸盐TIR发射数据。 在第一项任务中，他们将使用现有的实验室FTIR光谱仪和最近制造的微型炉来提供硅酸盐玻璃和熔体的诊断TIR吸收带位置/形状的第一个系统表征。 具体而言，他们将在实验室研究中重点关注三种状态：（1）高于固相线和玻璃化转变温度的样品，（2）冷却后最初在熔岩和矿物熔体上形成的玻璃状结壳，以及（3）矿物和天然岩石样品的最终间隙基质玻璃。 他们将收集实验室光谱仪的全部TIR光谱范围（5-25微米或2000-400 cm-1），但集中于地球大气窗口区域（8-12微米区域或1250-830 cm-1），以便将数据直接与卫星和实地收集的数据进行比较。 8-12微米区域也是硅酸盐矿物和玻璃中强吸收带（主要是Si-O和Al-O）的位置。拟议的研究将推进我们对红外光谱，分子尺度玻璃和熔体结构以及活性和非活性熔岩圆顶表面过程的理解。 然而，TIR光谱是一个准确的监测工具，影响发射的TIR能量从主动圆顶表面的因素必须得到更好的理解。 具体而言，TIR发射受冷却/冷却玻璃状结壳的形成、玻璃状基质的结构和百分比、其他涂层（例如升华物）以及中间气氛的影响。 本研究的第二个任务是基于实地的。 计划为P.I.采购波长滤波器。的TIR宽带相机，将其转换为基于场的光谱仪。从这一改进的仪器收集的数据将允许将实验室结果应用于非活动圆顶的现场数据。 这将是第一次以这种方式使用这种相机，希望它将导致最终建造一种坚固的监测仪器，能够部署在偏远的火山上，并用于监测和推导熔岩圆顶的基本物理特性（例如，表面泡囊度、斑晶组成和百分比、玻璃组成和百分比以及温度）。

Active silicic volcanoes commonly produce hazardous domes and flows that are erupted either as gas-rich lavas with a range of bubble and glass contents, or as denser piles of rubble and blocks like the ongoing eruption of Mt. St. Helens volcano. The former style can alternate between dome extrusion and hazardous explosive eruptions. The latter style is commonly less hazardous, but if large enough can still collapse catastrophically forming deadly block and ash flows. To assess the hazards associated with active lava domes, many pieces of information are needed including the dome's type/composition/temperature. However, it is typically too risky to collect hand samples directly (as was the case at during the first few weeks of the Mt. St. Helens eruption in 2004). Remote techniques for monitoring active lava dome composition and temperature are more desirable and the data best-suited for these measurements are in the thermal infrared (TIR) wavelength region. TIR data can be collected from space or field instruments, which are located safely away (several kilometers) from the active vent. TIR wavelengths are sensitive to both the emitted heat as well as the mineral composition of these domes. In order to quantitatively understand the TIR signal from natural lava domes, critical laboratory-based data are needed however. The investigators are proposing to collect data of natural glassy and molten materials in the laboratory using a micro-scale furnace developed under a previous grant in order to extend this research to the field by adapting a thermal camera (FLIR) to capture multispectral data, which will simulate the data collected from space. The research proposed has important theoretical implications for TIR spectroscopy/remote sensing data analysis as well as practical applications for volcanic hazard monitoring/mitigation. The laboratory results will be compared to field and satellite TIR data and will provide information that will aid development of the next-generation of field-based monitoring tools. This project will support a fruitful international collaboration and fund both a Ph.D.-level graduate student as well as a several undergraduate students.Specifically, it is proposed to do a follow-on research study comprised of laboratory and field-based tasks to characterize silicate TIR emission data produced by vibrations of the fundamental Si-(Al)-O units. In the first task, they will use their existing laboratory FTIR spectrometer and the recently-fabricated micro-furnace to provide the first systematic characterization of the diagnostic TIR absorption band positions/shapes of silicate glasses and melts. Specifically, they will focus on three states in the laboratory studies: (1) samples above the solidus and the glass transition temperatures, (2) the glassy crusts that initially form on lava and mineral melts upon cooling, and (3) the final interstitial matrix glass of mineral and natural silicic samples. They will collect the full TIR spectral range of the laboratory spectrometer (5-25 micrometer or 2000-400 cm-1), but concentrate on the region of the Earth''s atmospheric window (8-12 micrometer region or 1250-830 cm-1) in order to compare the data directly to those collected by satellite and from the field. The 8-12 micrometer region is also the location of the strong absorption bands (dominantly Si-O and also Al-O) in the silicate minerals and glasses. The proposed research will advance our understanding of infrared spectroscopy, molecular-scale glass and melt structure, and surface processes on both active and inactive lava domes. However, for TIR spectroscopy to be an accurate monitoring tool, the factors that affect the emitted TIR energy from active dome surfaces must be better-understood. Specifically, TIR emission is influenced by the formation of cooled/cooling glassy crusts, the structure and percentage of glassy matrix, other coatings such as sublimates, as well as the intervening atmosphere. The second task of this proposed research is field-based. It is planned to purchase wavelength filters for the P.I.'s TIR broadband camera that will convert it into a field-based spectrometer. The data collected from this modified instrument will allow an application of the laboratory results to field data of inactive silicic domes. This will be the first time such a camera will be used in this way and the hope is that it will lead to eventual construction of a rugged monitoring instrument capable of deployment on remote volcanoes and used for monitoring and derivation of fundamental physical properties of the lava dome (e.g., surface vesicularity, phenocryst composition and percentage, glass composition and percentage, and temperature) in real time.