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 Flows About 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.