Collaborative Research: The Spectral and Thermal Response of Active Basaltic Surfaces: Constraining Lava Cooling, Petrology and Flow Propagation Models

世界一半以上？S火山产生玄武岩熔岩，使其成为地球上最常见的火山活动形式。这些火山发生在每个构造环境和每个大陆上，过去与大规模灭绝事件有关的玄武岩熔岩喷发要大得多。最近，俄罗斯的托尔巴奇克(2012-2013年)、冰岛的巴尔达邦加(2014年)、意大利的埃特纳(2014年)和夏威夷的基拉韦厄(2014年)发生了新的喷发(或正在进行的喷发的新阶段)，强调了玄武岩喷发及其产生的熔岩流的持续危险潜力。例如，最近从夏威夷的Pu？u&amp；喷口喷出的熔岩流威胁到了这两处财产，如果继续推进，可能会孤立Pahoa镇的许多居民。因此，在这些情况下，监测熔岩的流动方向和速度变得至关重要。近年来引入了几个分析模型，旨在利用温度测量来估计熔岩流的推进，以便最终预测一旦充分冷却，熔岩流将在哪里停止。推进气流的温度通常是从地面、空气和轨道上用红外(IR)仪器测量的。然而，有许多因素可能会影响这些测量的准确性。如果对这些因素的假设是不正确的，那么测量温度的误差可能会对预测的潜在危险产生不利影响。其中一个假设是表面材料的发射率，它由表面的原子结构决定，并最终控制其辐射热量的效率。先前的发射率测量是在熔岩样本冷却成固体后进行的。然而，发射率并不是恒定的，实际上在熔岩中应该是变化的，因为原子结构已经发生了某种程度的变化。目前还没有对玄武岩熔岩的发射率进行定量测量，因此，这项研究旨在通过严格的实验室和现场数据收集，然后使用现有的流动模型进行测试，来进行这些复杂的测量。这项研究还将生产一种新的自动化野外红外仪器，可以用于任何负责火山喷发监测的政府机构。这项研究将建立在以前国家科学基金会资助的基础上，并继续匹兹堡大学研究小组与澳大利亚国立大学(澳大利亚)、帕斯卡大学(法国)和夏威夷火山观测站之间成功的国际合作。该项目还为纽约州立大学奥斯威戈分校的一名早期职业研究人员以及几名本科生和研究生提供资金。这项研究代表着遥感和流动模拟的阶段性变化，因为它第一次提供了关于喷发产品的最准确的红外温度数据，这些数据是预测危险和预测熔岩流动动力学所需的。了解活动玄武岩表面的冷却、形成和动力学不仅有助于解决流动中发生的成分、结构和硅酸盐结构变化，而且对于依赖准确的红外温度的任何测量或模型来说都是至关重要的。红外波长对辐射温度和表面发射率很敏感，这是因为矿物中存在由Si-O和Al-O键产生的强红外光谱带。因此，为了准确测量活动流动的温度，首先需要了解玻璃冷却结壳和熔融表面引起的光谱效应。这就是这项研究的总体目标，该研究分为两项主要任务：(1)以实验室为重点的研究，目的是使用与皮耶？S实验室光谱仪配合运行的独特微炉测量玄武岩玻璃和熔体的红外发射率；(2)现场研究，目的是改进现有的能够收集类似数据的红外仪器。在任务一下获得的实验室测量将在高温玄武岩熔体上进行，准确度超过2%。这些结果将澄清一个长期存在的争论，即熔化表面的热红外发射率是否低于相应的冷却表面(更根本的是，如果是这样的话？为什么？)。此外，它将提供数据，以解决冷却过程中正在进行的原子键尺度过程，因此还将允许重建过去熔岩流动的冷却历史。这些结果将作为第二项任务期间收集的地面数据的校准。将使用为该项目开发的新的多光谱红外仪器对活跃的玄武岩流动进行测量。这将是第一次使用红外相机获取光谱数据而不是温度数据，未来的发展将导致建造一种能够部署在偏远火山上的坚固型仪器，用于近乎实时地监测熔岩流的基本物理性质。最后，实验室和现场测量的结果将作为FLOWGO热流变模型的输入，以确定它们对模型估计的流动长度、粘度和速度的最终影响。所有这些结果都将适用于基于卫星的温度测量，因此有可能开辟岩石学、流动模拟和火山学遥感研究的全新领域。

Over half of the world?s volcanoes produce basaltic lava, making it the most common form of volcanic activity on Earth. These volcanoes occur at every tectonic setting and on every continent with much larger outpourings of basaltic lava in the past linked to mass extinction events. Recently, new eruptions (or new phases of ongoing eruptions) have occurred at Tolbachik in Russia (2012-2013); Bardarbunga in Iceland (2014); Etna in Italy (2014); and Kilauea in Hawaii (2014) emphasizing the ongoing hazard potential of basaltic eruptions and the lava flows they produce. For example, a recent lava flow from the Pu?u ?Ō?ō vent in Hawaii threatened both property and to potentially isolate many of the residents in the town of Pahoa had it continued to advance. Therefore, monitoring lava flow direction and velocity becomes critical in these situations. Several analytical models have been introduced in recent years that are designed to estimate lava flow advance using temperature measurements in order to ultimately predict where the flow will stop once it has cooled sufficiently. The temperature of the advancing flow is commonly measured with infrared (IR) instruments from the ground, air, and from orbit. However, there are many factors that can affect the accuracy of these measurements. If assumptions of these factors are incorrect, then errors in the measured temperature could adversely impact the predicted hazard potential. One of these assumptions is the emissivity of the surface material, which is determined by the atomic structure of the surface and ultimately controls how efficiently it radiates heat. Prior emissivity measurements have been made on lava samples once they have cooled to a solid. However, emissivity is not constant and should in fact vary in molten lava because the atomic structure has changed to some degree. There are no quantitative emissivity measurements of molten basaltic lava that exist and therefore this research is designed to make these complex measurements using rigorous laboratory and field data collection followed by testing using an existing flow model. The study will also produce a new automated field-based IR instrument that could be of use to any government agency charged with eruption monitoring. The research will build on prior NSF-funding and continue successful international collaborations between the research group at the University of Pittsburgh and the Australian National University (Australia), the Université Blaise Pascal (France) and the Hawaii Volcano Observatory. The project also provides funding for an early career researcher at SUNY Oswego as well as several undergraduate and graduate students. This research represents a step-change in both remote sensing and flow modeling because it supplies, for the first time, the most accurate IR temperature data on eruption products that are needed to forecast hazards and predict lava flow dynamics. Understanding the cooling, formation and dynamics of active basaltic surfaces will not only help to resolve compositional, textural, and silicate structural changes occurring in the flow, but also becomes critical for any measurement or model reliant upon accurate IR temperatures. The IR wavelengths are sensitive to radiant temperature as well as to the surface emissivity due to the presence of strong IR spectral bands, produced by the Si-O and Al-O bonds in the minerals. Therefore, in order to measure the accurate temperature of active flows it is first necessary to understand the spectral effects caused by the glassy cooling crusts and the molten surfaces. That is the overarching goal of this research, which is divided into two primary tasks: (1) a laboratory-focused study with the goal of measuring the IR emissivity of basaltic glasses and melts using a unique micro-furnace that operates in conjunction with the PI?s laboratory spectrometer; and (2) a field-based study with the goal of advancing existing IR instrumentation capable of collecting similar data. The laboratory measurements acquired under task one will be made on high temperature basaltic melts with an accuracy of greater than 2%. These results will clarify a long-standing debate of whether thermal IR emissivity of molten surfaces is lower than that of the corresponding cooled surfaces (and more fundamentally, if so ? why?). Furthermore, it will provide data to resolve atomic bond-scale processes ongoing during cooling and therefore will also allow for the reconstruction of the cooling history of past lava flows. These results will serve as calibration for the ground-based data collected during the second task. Measurements will be made of active basalt flows using a new multi-spectral IR instrument developed for this project. This will be the first time that an IR camera will be used to acquire spectral rather than temperature data, with future development leading to construction of a ruggedized instrument capable of deployment on remote volcanoes for monitoring fundamental physical properties of lava flows in near real time. Finally, the results from both the laboratory and field measurements will serve as input into the FLOWGO thermo-rheologic model in order to determine their final effects on the model estimated flow length, viscosity and velocity. All of these results will be applicable to satellite-based measurements of temperature and thus has the potential to open entirely new areas of petrology, flow modeling and volcanological remote sensing research.