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

火山爆发的产物通常包括空气中的玻璃灰，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远处的居民以及飞越的飞机造成危险，最近冰岛埃亚菲亚德拉火山爆发就是明证。火山爆发也会产生熔岩流、熔岩丘和火山碎屑流，这些对附近的人口中心都是危险的。这种类型的活动的例子是在最近的火山爆发。圣海伦斯（WA）和Mt.斯普尔火山（AK）以及正在进行的基拉韦厄（HI）喷发。这项研究的基本目标是通过研究这些熔岩流和圆顶的表面来更好地了解火山喷发过程。熔岩穹丘可以作为富含气体的岩石喷发，在熔岩挤出和危险的爆炸性喷发之间交替出现一系列气泡和玻璃成分。相比之下，玄武岩熔岩流在更高的温度下侵位，并在暴露于空气后迅速形成冷却的玻璃壳。由于在火山爆发期间直接采集手样通常风险太大，因此定量遥感探测技术变得极为宝贵。能够确定超过流动表面的温度允许一个约束喷发条件，通过确定矿物，挥发性和囊泡的百分比。计划使用在现场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。玻璃和囊泡都对TIR数据有可检测的影响，但是这种影响还没有很好地量化，也没有很好地理解熔融表面TIR发射的基本物理学。为了进行这项研究，匹兹堡大学地质和行星科学系将首次采用这种微型炉组件。这个熔炉（在以前的NSF资助下制造）能够熔化岩石样品，并直接连接到实验室发射光谱仪。它将允许在TIR数据中量化玻璃和囊泡的光谱效应。将在HI的基拉韦厄火山的活跃熔岩流处使用类似的程序，使用专门适用于收集多个光谱波段数据的TIR相机。这将允许直接比较实验室和现场数据（以及从轨道收集的TIR数据）。该研究将首次系统地表征这些材料的诊断光谱带位置和形状，并将这些结果应用于更好地了解熔岩流就位和冷却时正在进行的小尺度过程。这项研究对熔岩流动冷却的物理学和与它们就位速度有关的风险有直接的影响。此外，还将在全内反射照相机的基础上开发一个自动化实地全内反射监测系统，这将有助于对地球仪周围的流动和圆顶进行火山灾害监测，为了定量了解天然熔岩圆顶的全内反射信号，需要关键的实验室和实地数据。TIR波长对硅酸盐材料的表征敏感，因为在地球大气的透明区域（~ 8-12微米; 1250-833 cm-1）中存在强吸收带（主要是Si-O和Al-O）。为了准确地分析发射光谱并定量地提取熔岩的基本物理性质（例如，表面气泡、斑晶和玻璃成分/百分比和温度），有必要了解玻璃质结壳和熔融物质的光谱效应。这项工作将提供这些材料的诊断吸收带位置和光谱形状的第一个系统的表征，分为两个主要任务。第一个任务是实验室为重点的目标是提供第一个系统的表征诊断TIR吸收带的位置/形状的玄武玻璃和熔体。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）矿物和天然样品的最终间隙基质玻璃。他们将收集实验室光谱仪的全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。第二项任务是以实地为基础，目标是开发能够收集类似TIR数据的TIR仪器，并最终作为监测工具部署。从多光谱TIR照相机收集的数据应允许使用从活跃玄武岩流收集的数据验证实验室结果。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和流动的基本物理特性，在真实的时间。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流表面过程的理解。

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.