Quantifying degassing-driven crystal growth in basaltic lavas

熔岩流研究的一个主要目的是开发精确的流动模型，用于预测淹没区域，并估计熔岩在停止之前将前进多远。熔岩流是复杂的流体，包括晶体、液体和气泡的混合物，当它们流动时，它们冷却并失去最初在表面下的高压下溶解在熔体中的挥发性物质（主要是水和二氧化碳）。冷却和脱气都会导致液态熔体结晶，从而对流动提前产生显著影响。冷却是结晶的主要驱动力，但其影响主要限于热边界层，在那里它是形成表面地壳和横向水平的一个整体过程。相比之下，脱气不限于边界层，并且在整个流动中发生，具有影响整个本体流变学的潜力。虽然冷却驱动的结晶的影响占在当前一代的熔岩流模型，晶体生长由于脱气尚未得到充分的量化，使其纳入模型。在最近的实验室实验中，我们已经能够同时测量脱气和结晶的第一次，我们建议进一步研究直接使用热台显微镜检查晶体的生长。这将提供有关晶体尺寸、生长速率和形态的数据，以量化脱气对熔岩整体结晶的贡献。最终，这些结果将允许脱气引起的结晶在数值熔岩流模型占。

A primary aim of lava flow research is the development of accurate flow models that can be used to forecast areas of inundation, and to estimate how far lavas will advance before stopping. Lava flows are complex fluids comprising mixtures of crystals, liquid and gas bubbles and, as they flow, they cool and lose volatile species (mainly water and carbon dioxide) that were initially dissolved in the melt at high pressure beneath the surface. Both cooling and degassing lead to crystallisation of the liquid melt, and thus have significant influence on flow advance. Cooling is a major driver of crystallisation, but its effects are mainly restricted to the thermal boundary layers, where it is an integral process in the formation of surface crust and lateral levées. In contrast, degassing is not restricted to boundary layers and occurs throughout flows, with the potential to affect the entire bulk rheology. Although the effects of cooling-driven crystallisation are accounted for in the current generation of lava flow models, crystal growth due to degassing has not yet been sufficiently quantified to allow its incorporation into models. In recent laboratory experiments, we have been able to simultaneously measure degassing and crystallisation for the first time, and we propose to further this research by examining the growth of crystals directly using hot stage microscopy. This will provide the data on crystal sizes, growth rates and morphologies necessary to quantify the contribution of degassing to the overall crystallisation of lavas. Ultimately, these results will allow degassing-induced crystallisation to be accounted for in numerical lava flow models.