What happens to the ash in underwater eruptions? Numerical modeling of syn-eruptive ash and lapilli partitioning in the water column

Abstract:

Ash and lapilli transport in subaqueous eruptions is studied using computational models to quantify material partitioning in the water column by volcanic jets. One of the principal objectives of volcanology is to determine where and how erupted material is transported, with the ambition of anticipating hazards of future eruptions. To achieve this, a necessary connection must be established between eruption transport dynamics and tephra emplacement. In subaerial explosive eruptions, it has been shown that the distribution of erupted material is primarily dictated by high-velocity, turbulent gas jets. These jets link the dynamics of the conduit with atmospheric tephra dispersal. While this relationship is most certainly mirrored in submarine explosive eruptions, a lack of measurements and observations has prevented the direct correlation of gas jet dynamics with tephra emplacement and dispersal in the water column. We utilize the multiphase subaqueous eruption model of Cahalan and Dufek (2020) to characterize the emplacement of particles in different zones of the water column. Simulations were conducted for a range of particle diameters (1e-6 – 1e-2 m), concentrations (1e-5 – 1e-1 particle volume fraction), particle densities (200 – 3000 kg/m³), as well as a range of mass eruption rates (1e5 – 1e8 kg/s), eruption temperatures (700-1300 ^oC), and water depths (50 – 1000 m). In addition to comparing results for different particle parameters and eruption conditions, we present results for condensable gas jets (driven by water vapor) and gas-less simulations to assess the importance of considering condensable gas jets in subaqueous eruption models.