Estimates of condensed water in and energetics of the Hunga volcanic plume on 15 January 2022
摘要
Systematic calculations are made for the volume of the January 15, 2022 Hunga Volcano plume. We use inferred atmospheric water concentrations to estimate the mass of H2O condensate in the plume. A cylinder 58 km high (early) and radius 15 km for the core and a disk 10 km thick for the umbrella cloud provide an estimate of the plume volume. 1.3–5 g/m3 as the water concentration for the core and 1.3 g/m3 for the umbrella cloud give the H2O plume loading. The 58-km-high (maximum) plume height was transient, and the huge umbrella cloud reached a maximum 30–60 min later. Although the thickness of the umbrella cloud is poorly known, it is likely thicker near the volcano and thinner at leading edges. Plume volume estimates were made every 10 min, coinciding with the timing of satellite images, and the peak values were recorded when the umbrella reached its maximum size at 0520 UTC. Umbrella thicknesses were assumed to be 10 km. Lidar images (Calipso) show thickness of the ash-rich part of the plume to be 2–2.5 km. The estimates for the mass of water range from 2.7 to 3.5 × 1012 kg. Estimates for magma volume range from 1.8 to 5 km3. An upper estimate of the amount of water in pristine andesitic magma, using 2600 kg/m3 density, 3–5 wt % water, and 6.85 km3 magma, is 5.4–8.9 × 1011 kg, a factor of 3–4 lower than the plume water content. We thus infer that circa 80% of the water in the plume is from seawater flashed to steam. These estimates constrain the source characteristics, seeking agreement in mass and heat using an isentropic explosive energy model. These include magma eruptive volume, plume water content, magma reservoir initial conditions, the heat needed to flash seawater to steam, and the explosive yield. The observed and modeled explosion energy of the 2022 Hunga eruption is comparable to that of Krakatau in 1883 (~ 100–200 Mt TNT), despite the Hunga eruption being 2 to 4 times less voluminous. This contrast is explained by the ingestion of copious amounts of seawater and its subsequent vaporization and expansion compared to the drier Krakatau eruption.