Rheological Evolution of Basaltic Lava Flows During Cooling and Crystallization

玄武岩熔岩覆盖了地球和其他几个行星和卫星的大部分表面。熔岩流的形态和其他结构，如圆锥体和穹顶，与熔岩的物理性质、渗出率和环境因素有关，如表面介质(海底与地面)和坡度。熔岩的重要物理性质包括粘度、屈服强度、热扩散率和热容量，所有这些都随温度(T)和结晶分数(&amp；#966；，其本身随T而变化)而变化。熔体粘度可以在一次喷发事件中变化许多数量级，尽管最近取得了进展，但结晶玄武岩岩浆的流变学仍然相对较差。PI和研究生将在适合玄武岩火山活动的条件下测量不同构造环境下玄武岩熔岩的流变性和热学性质，并模拟这些性质随T、成分(X)和&amp；#966；的函数变化。这样做的目的是为了更好地了解这些特性在特定时刻如何在流动中变化，以及在从喷口到最终侵位的一小部分岩浆中如何变化。通过结合岩浆流变学和热学性质的信息，我们试图探索结晶、潜热释放、熔体粘度和屈服强度之间潜在的复杂反馈关系，这些关系控制着整体流变学和流动形态。要研究的熔岩样本将来自基拉韦厄(夏威夷)、拉基(冰岛)、埃特纳(意大利)、富埃戈和帕卡亚(危地马拉)以及阿雷纳尔(哥斯达黎加)。实验测量将包括：使用平行板和同心圆筒粘度计测定熔体粘度，范围从1到1012Pa.s作为温度的函数。屈服强度将在与熔岩流动相关的低应力下通过测量应变率作为应力的函数来确定，用于精心挑选的时间序列实验，以获得不同晶体含量的样品。液体热容和熔化热将用滴量热法测定。玻璃和过冷液体的热容和过冷条件下的结晶热将用差示扫描量热法测定。熔体粘度和多相岩浆流变性(有效粘度和表观屈服强度)将作为T、X和&amp；的函数进行参数化。该研究计划将被分成几个较小的项目，将为研究生和本科生的综合培训和教育提供许多机会。该项目将提供应用于自然灾害、行星地质学和材料科学的数据和模型。

Basaltic lavas cover large portions of the surface of the Earth and several other planets and moons. The morphology of lava flows and other structures such as cones and domes is related to the physical properties of the lava, the effusion rate, and environmental factors such as surface medium (submarine vs subaerial) and slope. Important physical properties of lavas include viscosity, yield strength, thermal diffusivity and heat capacity, all of which vary with temperature (T) and crystal fraction (φ, which itself varies with T). Melt viscosity can vary by many orders of magnitude within a single eruptive event, and despite recent advances the rheology of crystallizing basaltic magma is still relatively poorly constrained. The PI and graduate students will measure the rheological and thermal properties of basaltic lavas from various tectonic settings at conditions appropriate to basaltic volcanism, and model variations in these properties as a function of T, composition (X) and φ. The aim is to provide a better understanding of how these properties can vary across a flow at a particular instant in time, and within a single quantum of magma from vent to final emplacement. By combining information on rheological and thermal properties of magma, we seek to explore potentially complex feedback relationships between crystallization, latent heat release, melt viscosity and yield strength that control the overall rheology and flow morphology. The lava samples to be studied will come from Kilauea (Hawaii), Laki (Iceland), Etna (Italy), Fuego and Pacaya (Guatemala), and Arenal (Costa Rica). Experimental measurements will include: determination of melt viscosity from 1 to 1012 Pa.s as a function of temperature, using parallel-plate and concentric-cylinder viscometers. Yield strength will be determined at low stresses relevant to lava flows by measuring strain rate as a function of stress, for carefully selected time series experiments to obtain samples with different crystal contents. Liquid heat capacity and the enthalpy of fusion will be determined by drop calorimetry. Heat capacity of glasses and supercooled liquids, and enthalpy of crystallization under supercooled conditions, will be determined by differential scanning calorimetry. Melt viscosity and multiphase magma rheology (effective viscosity and apparent yield strength) will be parameterized as a function of T, X and φ. The research program will be divided into smaller projects that will provide many opportunities for integrated graduate and undergraduate training and education. The project will provide data and models with applications extending to natural hazards, planetary geology and materials science.