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The dynamics of deep-submarine explosive eruptions

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Deposits from explosive submarine eruptions have been found in the deep sea, 1–4 km below the surface, with both flow and fall deposits extending several km’s over the seafloor. A model of a turbulent fountain suggests that after rising 10–20 m above the vent, the erupting particle‑laden mixture entrains and mixes with sufficient seawater that it becomes denser than seawater. The momentum of the resulting negatively buoyant fountain is only sufficient to carry the material 50–200 m above the seafloor and much of the solid material then collapses to the seafloor. The deep-ocean is also host to both local and large-scale currents, with magnitudes varying in the range ua = 0.01-1.0 ms-1 . We explore the interaction of these currents with such fountains through a series of novel laboratory experiments in which particle-laden fountains rise through a uniform crossflow. Using our experimental observations, we categorise the dynamics of these particle-laden fountains in terms of the ratios of (i) the particle fall speed to the fountain speed, and (ii) the current speed to the fountain speed. Using the experimental results, we develop and test simple quantitative estimates for the average rise height and particle dispersal distance based on the motion of single-phase fountains in a crossflow. We apply these results to predict the control of eruption rate, ambient currents and particle size distribution on the dispersal of volcanic particles following deep submarine explosive eruptions.

This talk is part of the Seminars for the Institute for Energy and Environmental Flows (formerly BP Institute) series.

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