Infrared Spectroscopy of Melts: New Approaches to Understanding Lava Flow Emplacement

火山喷发的产物通常包括空气中的玻璃状火山灰，以及二氧化硫、水蒸气和二氧化碳等气体。火山灰和气体可能对遥远的人群和飞越的飞机构成危险，最近冰岛埃亚菲亚德拉火山喷发就证明了这一点。火山喷发还会产生熔岩流、熔岩穹顶和火山碎屑流，这些对附近的人口中心来说大多是危险的。在最近的火山喷发中就可以看到这种活动的例子。圣海伦斯(华盛顿州)和Mt.Spur(AK)以及正在进行的基拉韦厄火山喷发(HI)。这项研究的基本目标是通过研究这些熔岩流和穹顶的表面来更好地了解火山喷发过程。熔岩穹顶可以作为富含气体的岩石喷发，其气泡和玻璃成分在熔岩挤出和危险的爆炸性喷发之间交替。相比之下，玄武岩熔岩流的侵位温度要高得多，并在暴露在空气中后迅速形成冰冷的玻璃外壳。由于在火山喷发期间直接采集手部样本通常风险太大，定量远程探测技术变得非常有价值。通过测定矿物、挥发分和水泡的百分比，不仅可以确定流动表面的温度，还可以限制喷发条件。它计划使用在野外和实验室收集的热红外(TIR)数据来分析这些玻璃状熔岩表面。玻璃和气泡对TIR数据都有可检测到的影响，然而这种影响还没有得到很好的量化，熔融表面TIR发射的基本物理也没有被很好地理解。为了进行这项研究，将使用匹兹堡大学地质和行星科学系的第一个此类微炉组件。这个熔炉(根据之前的NSF资助建造)能够熔化岩石样品，并直接连接到实验室发射光谱仪。它将使玻璃和囊泡的光谱效应在TIR数据中得以量化。类似的程序将用于HI基拉韦厄火山的活动熔岩流，使用专门用于收集多光谱波长波段数据的TIR相机。这将使实验室数据和现场数据(以及从轨道收集的TIR数据)之间能够进行直接比较。这项研究将首次系统地描述这些物质的诊断光谱带位置和形状，并应用这些结果来更好地理解熔岩流侵位和冷却时正在进行的小尺度过程。这项研究对熔岩流动如何冷却的物理学有直接影响，并与它们侵位的速度有关的风险。此外，还将开发一个基于TIR相机的野外TIR自动监测系统，这将有助于对全球各地的流动和穹顶进行火山灾害监测。为了定量了解来自天然熔岩穹顶的TIR信号，需要关键的实验室和现场数据。TIR波长对硅酸盐材料的表征很敏感，因为在地球大气的透明区域(约8-12微米；1250-833厘米-1)存在强吸收带(主要是Si-O和Al-O)。为了准确分析发射光谱并定量提取熔岩的基本物理性质(如表面气泡度、斑晶和玻璃成分/百分比和温度)，有必要了解玻璃结壳和熔融物质的光谱效应。这项工作将首次系统地表征这些材料的诊断吸收带位置和光谱形状，分为两项主要任务。第一项任务以实验室为重点，目的是首次系统地描述玄武岩玻璃和熔体的诊断TIR吸收带位置/形状。具体地说，他们将重点研究实验室研究中的三种状态：(1)高于固相线和玻璃转变温度的样品，(2)冷却时最初在熔岩和矿物熔体上形成的玻璃结壳，以及(3)矿物和天然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)，但集中在地球大气窗口区域(8-12微米区域或1250-830厘米-1)，以便直接与卫星和实地收集的数据进行比较。第二项任务是以实地为基础，目标是开发能够收集类似的国际热辐射数据并最终可作为监测工具部署的国际热辐射仪器。从多光谱TIR相机收集的数据应该可以利用从活跃的玄武岩流动收集的数据来验证实验室结果。这将是第一次以这种方式使用这种相机，希望它最终将导致建造一种坚固耐用的监测仪器，能够部署在偏远的火山上，用于实时监测和得出熔岩穹顶和流动的基本物理性质。拟议的研究将促进我们对红外光谱、分子尺度玻璃和熔体结构以及活动和非活动熔岩流动的表面过程的理解。

The products of volcanic eruptions commonly include airborne glassy ash, and gases such as sulfur dioxide, water vapor and carbon dioxide. The ash and gas can pose hazards to distant populations as well as overflying aircraft, as was evident during the recent eruption of Eyjafjallajökull in Iceland. Eruptions can also produce lava flows, lava domes and pyroclastic flows that are hazardous mostly to nearby population centers. Examples of this style of activity were seen at the recent eruptions of Mt. St. Helens (WA) and Mt. Spurr (AK) as well as at the ongoing eruption at Kilauea (HI). The fundamental goal of this research is to better understand volcanic eruption processes by studying the surfaces of these lava flow and domes. Lava domes can erupt as gas-rich rocks with a range of bubble and glass contents alternating between lava extrusion and hazardous explosive eruptions. In contrast, basaltic lava flows are emplaced at much higher temperatures and rapidly form a chilled glassy crust after exposure to air. Because it is commonly too risky to collect hand samples directly during a volcanic eruption, quantitative remote detection techniques have become extremely valuable. Being able to determine more than the temperature of a flow surface allows one to constrain the eruption conditions through determination of the mineral, volatile and vesicle percentages. It is planned to use thermal infrared (TIR) data collected in the field and in the laboratory to analyze these glassy lava surfaces. Both glass and vesicles have a detectable effect on TIR data, however this effect has not been well quantified nor is the fundamental physics of TIR emission from molten surfaces well understood. In order to carry out this research, a first of its kind micro-furnace assembly at the Department of Geology and Planetary Science, University of Pittsburgh will be employed. This furnace (fabricated under previous NSF funding) is capable of melting rock samples and is directly attached to a laboratory emission spectrometer. It will allow the spectral effects of glass and vesicles to be quantified in TIR data. A similar procedure will be used at the active lava flows of Kilauea volcano, HI using a TIR camera specially adapted to collect data in multiple spectral wavelength bands. This will allow a direct comparison between the lab and field data (as well as TIR data collected from orbit). The research will provide the first systematic characterization of the diagnostic spectral band positions and shapes of these materials and apply those results to better understand the small scale processes ongoing as a lava flow is emplaced and cools. This research has immediate implications on the physics of how lava flows cool and risks involved with how fast they are emplaced. In addition, an automated field-based TIR monitoring system will be developed based on the TIR camera, which will aid in volcanic hazard monitoring of flows and domes around the globe.To quantitatively understand the TIR signal from natural lava domes, critical laboratory- and field-based data are needed. The TIR wavelengths are sensitive to the characterization of silicate material because of the presence of strong absorption bands (dominantly Si-O and also Al-O) in the clear region of the Earth's atmosphere (~ 8-12 micrometers; 1250-833 cm-1). In order to accurately analyze the emitted spectra and quantitatively extract the fundamental physical properties of the lava (e.g., surface vesicularity, the phenocryst and glass composition/percentage and temperature) it is necessary to understand the spectral effects of the glassy crusts and molten material. This work will provide the first systematic characterization of the diagnostic absorption band positions and spectral shapes of these materials and is divided into two primary tasks. The first task is laboratory-focused with the goal of providing the first systematic characterization of the diagnostic TIR absorption band positions/shapes of basaltic 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 samples. They will collect the full TIR spectral range of the laboratory spectrometer (5-25 micrometers or 2000-400 cm-1), but concentrate on the region of the Earth's atmospheric window (8-12 micrometers region or 1250-830 cm-1) in order to compare the data directly to those collected by satellite and from the field. The second task is field-based with the goal of developing TIR instrumentation capable of collecting similar TIR data and which can eventually be deployed as a monitoring tool. The data collected from the multispectral TIR camera should allow validation of the laboratory results using data collected from active basaltic flows. 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 lava domes and flows in real time. 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 flows.