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

硅玻璃和熔体的红外光谱：从实验室规模的测量得出火山规模的过程

• 批准号: 0711056
• 负责人: Michael Ramsey
• 金额: $ 26.67万
• 依托单位: University of Pittsburgh
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-07-01 至 2011-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0711056&HistoricalAwards=false
• 关键词: Infrared; Spectroscopy; Silicic; Glasses; Melts

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.

活跃的硅质火山通常会产生危险的圆顶和水流，这些圆顶和水流要么以富含气体的熔岩的形式喷发出来，其中含有一系列气泡和玻璃，要么像正在喷发的圣海伦斯火山那样形成密度更大的碎石和石块堆。前一种方式可以在圆顶挤压和危险的爆炸喷发之间交替进行。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，形成致命的块体和火山灰流。为了评估与活动熔岩穹丘相关的危害，需要许多信息，包括穹丘的类型/组成/温度。然而，直接采集手部样本通常风险太大（就像2004年圣海伦斯火山爆发前几周的情况一样）。监测活动熔岩穹窿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数据可以从太空或野外仪器收集，这些仪器位于距离活动喷口安全（几公里）的地方。TIR波长对发射的热量和这些圆顶的矿物成分都很敏感。然而，为了定量地了解天然熔岩穹丘的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先前拨款开发的微型炉来收集天然玻璃和熔融材料的数据，以便通过采用热像仪（FLIR）来捕获多光谱数据，从而将该研究扩展到现场，这将模拟从太空收集的数据。提出的研究对红外光谱/遥感数据分析以及火山灾害监测/减灾的实际应用具有重要的理论意义。实验室结果将与现场和卫星TIR数据进行比较，并将提供有助于开发下一代现场监测工具的信息。该项目将支持富有成效的国际合作，并资助一名博士研究生和几名本科生。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。在第一个任务中，他们将使用他们现有的实验室FTIR光谱仪和最近制造的微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。具体来说，他们将在实验室研究中关注三种状态：(1)高于固相和玻璃化转变温度的样品，(2)冷却后熔岩和矿物熔体上最初形成的玻璃状外壳，以及(3)矿物和天然硅样品的最终间隙基质玻璃。他们将收集实验室光谱仪的整个TIR光谱范围（5-25微米或2000-400厘米-1），但将重点放在地球大气窗口区域（8-12微米区域或1250-830厘米-1），以便将数据直接与卫星和野外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。本研究将促进我们对红外光谱、分子尺度的玻璃和熔体结构以及活性和非活性熔岩穹丘表面过程的理解。然而，为了使TIR光谱成为一种准确的监测工具，必须更好地了解影响活跃圆顶表面发射的TIR能量的因素。具体来说，TIR发射受到冷却/冷却玻璃结壳的形成、玻璃基体的结构和百分比、其他涂层（如升华物）以及中间大气的影响。这项拟议研究的第二个任务是基于实地的。计划为pi购买波长滤波器它将把它转换成一个现场光谱仪。从这种改进的仪器中收集的数据将允许将实验室结果应用于非活性硅圆顶的现场数据。这将是第一次以这种方式使用这样的相机，希望它将导致最终构建一个坚固的监测仪器，能够部署在偏远的火山上，用于实时监测和导出熔岩圆顶的基本物理特性（例如，表面水泡，斑晶成分和百分比，玻璃成分和百分比，以及温度）。