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Abstract:
Systematic calculations were made of the volume of the January 15, 2022 Hunga Tonga Hunga Ha’apai plume. We first estimate volume of the plume, then use inferred atmospheric water concentrations to estimate the amount of water. For plume volume, we used a cylinder 58 km high and radius 5 km for the core near the volcano, then a disk 10 km thick for the umbrella cloud. To get the amount of water, we used 15 g/m3 for the core (based on Alaskan volcanoes) and 1.5 g/m3 for the umbrella cloud (from thunderstorms). Note that the core concentration is 10x higher. We note: 1) The two parts are asynchronous. The 58-km-high part was transient, and the huge umbrella cloud was 30-60 min later; 2) thickness of the umbrella cloud is poorly known. It is likely thicker near the volcano and thinner at leading edges; and 3) water concentrations are between the two endmember values.Plume volume estimates were made every 10 minutes. Umbrella thicknesses were assumed 10 km. Areas are measured from satellite images. Lidar images (Calypso) show thickness of the ash-rich part of the plume (2-2.5 km). The estimates for the amount of water range from 3-9 x 1015 g.Estimates of the amount of water in magma, using 2600 Kg/m3 density, 5 wt % water, and 6 km3 magma, are 8 x 1014 g, an order of magnitude lower than plume estimates. We thus infer that 90 percent of the plume is from seawater flashed to steam.
