The effects of degassing and effusion rate fluctuations on the evolution of basaltic lava flow

玄武岩熔岩流对许多火山的财产和基础设施造成重大损害。为了提高我们对熔岩流场演化的认识，有必要对熔岩从喷口向流锋移动过程中的物理化学性质以及流动过程中发生的复杂相互作用进行多学科综合研究。关键要求是：(i)预测熔岩流变在流动过程中如何变化的可靠方法；以及（ii）对长期和短期的积液率变化如何影响流动就位过程中操作的复杂过程范围的更好理解。该项目将使用新的现场设备、自动成像程序、地面、直升机和卫星成像以及创新的实验室测量提供一系列测量。合并后的数据集将用于开发和约束下一代熔岩流模型，这些模型将推动未来对玄武岩火山的危害评估和缓解战略。我们建议把研究重点放在埃特纳火山的一次或多次喷发上。这个协作和多学科项目将由兰开斯特大学的PI和co -PI， INGV，卡塔尼亚的工作人员以及来自美国和英国的其他同事共同承担。目前的流动模型假设流变变化主要是由表面冷却驱动的。然而，整个流动厚度的流变变化可能是由于脱气相关的过冷结晶造成的。为了评估过冷的重要性，我们将确定在活动熔岩流就位期间挥发性损失的模式以及晶体和气泡成核和生长的速率，并使用新的现场粘度计精确测量活动熔岩流不同部分的熔岩流变特性。与INGV，卡塔尼亚和俄勒冈大学的同事合作，收集所有测量的熔岩的淬火样品，并用于确定所有样品的结晶度，泡状度和残余玻璃的组成。在兰开斯特，将使用最先进的x射线断层扫描仪进行囊泡大小分布、孔隙度以及气泡聚结和连通性评估（以及流动过程中气体损失的可能性）。放置过程中挥发性损失的测量将在兰开斯特的岩浆挥发性实验室进行，使用耦合热重分析-差示扫描量热计-质谱仪，这些将允许对过冷的潜在影响进行量化，并与晶体尺寸分布的变化进行比较。这些综合的实验室和现场测量将使我们第一次能够重建熔岩流的整个挥发性脱气预算，并评估脱气在控制熔岩流就位中的重要性。上述测量将与综合时间序列热图像和不断演变的熔岩流场的数字地形模型结合使用，以了解和量化流场演变的过程。数字地形模型将使用远程激光扫描仪数据创建，并通过来自新的高分辨率相机网络的地面图像的倾斜摄影测量数据进行增强。这些将由INGV、卡塔尼亚和Hyperion卫星与喷气推进实验室的同事合作收集的直升机图像进行补充。通过结合流变/脱气和成像测量获得的数据将首次使放置过程/流动行为与简单和更复杂的流场中的熔岩冷却、脱气和结晶直接联系起来。虽然这项工作将在埃特纳火山的熔岩上进行，但该项目中开发的方法在许多其他火山上都有重要应用，并且符合NERC 2007-2012年的战略和科学优先事项。

Basaltic lava flows cause significant damage to property and infrastructure on many volcanoes. To improve our understanding of the evolution of lava flows and flow fields, there is a need for an integrated multi-disciplinary study of the physicochemical properties of lava as it moves from the vent to the flow front, and of the complex interactions that take place during flow. Key requirements are: (i) robust methods of predicting how lava rheology changes during flow; and (ii) an improved understanding of how both long- and short-term changes in effusion rates affect the complex range of processes operating during flow emplacement. This project will provide a range of measurements using new field equipment, automated imaging procedures, ground-, helicopter- and satellite-based imagery and innovative laboratory measurements. The combined dataset will be used to develop and constrain the next-generation of lava flow models which will drive future hazard assessment and mitigation strategies on basaltic volcanoes. We propose to focus our research on one or more eruptions of Mount Etna. This collaborative and multi-disciplinary project will be undertaken jointly by the PI and Co-PIs at Lancaster, staff at INGV, Catania, and other colleagues from the USA and the UK. Current flow models assume that rheological changes are driven mainly by surface cooling. However, rheological changes over the entire flow thickness can result from crystallisation due to degassing-related undercooling. To assess the importance of undercooling, we will determine patterns of volatile loss and rates of crystal and bubble nucleation and growth during the emplacement of active lava flows, and make accurate measurements of the rheological properties of lava in different parts of an active lava flow using a new field viscometer. Quenched samples of all lavas measured will be collected and used to determine the crystallinity, vesicularity and composition of residual glass of all samples in collaboration with colleagues at INGV, Catania, and the University of Oregon. Vesicle size distributions, porosity and an assessment of bubble coalescence and connectivity (and hence the potential for gas loss during flow) will be made at Lancaster using a state-of-the-art X-ray tomographic scanner. Measurements of volatile loss during emplacement will be undertaken in a new Magma Volatile Laboratory at Lancaster using a coupled Thermogravimetric Analysis - Differential Scanning Calorimeter - Mass Spectrometer, and these will allow the potential effects of undercooling to be quantified and compared with changes in crystal size distribution. These combined laboratory and field measurements will allow us to reconstruct the entire volatile degassing budget of a lava flow for the first time, and to assess the importance of degassing in controlling the emplacement of lava flows. The above measurements will be used in combination with a comprehensive time-series of thermal images and digital terrain models of an evolving lava flow field to understand and quantify the processes responsible for flow field evolution. Digital terrain models will be created using long range laser scanner data, augmented by oblique photogrammetric data from ground-based imagery from a new network of high-resolution cameras. These will be supplemented by helicopter imagery collected by INGV, Catania, and Hyperion satellite data in collaboration with a colleague at the Jet Propulsion Laboratory. The data acquired using the combined rheological/degassing and imaging measurements will, for the first time, enable the emplacement processes/flow behaviour to be directly linked to the cooling, degassing and crystallisation of the lava in both simple and more complex flow fields. While the work will be undertaken on lavas from Mount Etna, the methodologies developed in this project have major applications for many other volcanoes and are in line with NERC's strategic and scientific priorities 2007-2012.