Collaborative Research: Experimental constraints on the solidification time scales and fragmentation of submarine lava flows

该奖项全部或部分由《2021年美国救援计划法案》（公法117-2）资助。海底熔岩流碎裂地球上大约75%的火山是在海底条件下喷发的。这个项目研究海底熔岩流和海水之间的相互作用。海底火山爆发时，熔岩与海水直接接触，海水迅速冷却熔岩，导致其表面形成固体地壳。这影响了海底熔岩流的速率和熔岩流形态的形成。对熔岩冷却时间尺度的不了解是我们在模拟海底熔岩流动力学方面的一个重大差距。本项目将利用实验室对融化的天然岩石进行实验，研究水的盐度、速度和温度对具有一系列成分的熔岩凝固时间尺度的影响。初步结果表明，一层水汽一旦与热熔岩样品直接接触就会形成。根据熔岩和水的温度，蒸汽膜破裂，在熔岩-水界面形成许多气泡，并改变样品的热损失率。该项目将(1)研究熔岩冷却过程中蒸汽膜的开始和稳定性；(2)量化一系列熔岩和水温的冷却时间尺度；(3)研究水的盐度、水流速度和熔岩成分对熔岩冷却的影响；(4)评估海底熔岩流形态的形成方式。该项目将培养本科生和研究生，并将为早期职业研究者提供研究支持。最先进的实验设施将独特地放置在美国西南部，促进国内和国际合作。了解熔岩形态形成背后的条件对于估计海底熔岩流的流出率和动力学具有重要意义。从熔岩到外部水的热通量是决定海底熔岩凝固时间尺度和流动动力学的关键量之一。目前还没有对熔岩与水交界面热流的直接现场测量。为了估计熔岩到水的传热速率，目前的模型假设了一个对流的水流状态，或者使用现有金属-水传热研究中的热流密度参数。由于熔岩的导热系数比金属低得多，现有的金属-水传热研究的传热公式需要实验验证，如果有必要，需要开发新的理论框架。该项目将使用一种新颖的实验方法来量化外部水存在下的熔岩冷却速率，使用的熔岩样本来自硅质到基性成分的重熔岩石。水的沸腾状态及其与热熔岩直接接触的持续时间将由实验确定。水的温度、速度和盐度将在一个适合潜艇条件的范围内变化。实验样品的温度依赖性热物理性质将被测量。利用热传递模型中熔岩样品的这些良好约束性质，估算熔岩到水的对流热通量。通过将实验和数值分析与理论发展相结合，该项目将为研究外部水存在下熔岩凝固时间尺度提供一个整体方法。在这个项目中，将开发导热性差的熔岩到外部水的传热的新理论框架。这将促进我们对海底熔岩凝固时间尺度的认识，从而为提高我们对海底火山喷发动力学的认识提供重要的基础。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Fragmentation of Submarine Lava FlowsAbout 75 percent of volcanoes on Earth erupt under submarine conditions. This project deals with investigating the interaction between submarine lava flows and seawater. As lava comes in direct contact with seawater during submarine volcanic eruptions, the water cools the lava rapidly causing the formation of solid crust on its surface. This affects the rates of submarine lava flows, and the formation of lava flow morphologies. Poor understanding of lava cooling time scales is a significant gap in our ability to model the dynamics of submarine lava flows. Using laboratory experiments with melted natural rocks, this project will investigate the effects of salinity, speed, and temperature of water on the solidification time scales of lavas with a range of compositions. The preliminary results indicate that a film of water vapor forms as soon as it comes in direct contact with the hot lava sample. Depending on the lava and water temperatures, the vapor film breaks down forming numerous bubbles at the lava-water interface and changing the rate of heat loss from the sample. This project will (1) investigate the onset and stability of vapor film during the cooling of lava, (2) quantify the cooling time scales for a range of lava and water temperatures, (3) investigate the effects of water salinity, water speed and lava composition on the cooling of lava, (4) evaluate how submarine lava flow morphologies are formed. This project will train undergraduate and graduate students, and will provide research support to early career investigators. The state-of-the-art experimental facility will be uniquely placed in the southwest US facilitating national and international collaborations. Understanding the conditions behind the formation of lava morphologies is important for estimating effusion rates and dynamics of submarine lava flows. The heat flux from lava to external water is one of the key quantities that govern the solidification time scales and thus the flow dynamics of submarine lavas. The direct field measurement of heat flux at the interface of lava and water is currently absent. Current models assume a convective water flow regime or use heat flux parameters from existing metal-to-water heat transfer studies in order to estimate the rate of heat transfer from lava to water. Due to much lower thermal conductivity of lava as compared to metals, the existing heat transfer formulations from metal-to-water heat transfer studies require experimental validation, and if necessary, new theoretical frameworks need to be developed. This project will use a novel experimental approach to quantify the lava cooling rates in the presence of external water using lava samples from remelted rocks of silicic to mafic compositions. The water boiling regimes and their duration in direct contact with hot lava will be determined from the experiments. The temperature, speed and salinity of water will be varied for a range suitable under submarine conditions. The temperature-dependent thermophysical properties of the experimental samples will be measured. Using these well-constrained properties of the lava sample in the heat transfer model, the convective heat flux from lava to water will be estimated. By integrating experimental and numerical analyses with theoretical development, the project will provide a holistic approach for studying the solidification time scales of lava in the presence of external water. New theoretical frameworks for heat transfer from thermally poor conductive lava to external water will be developed in this project. This will advance our understanding of submarine lava solidification time scales, and will thus provide an important basis to improve our understanding of the dynamics of submarine volcanic eruptions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.