Airfall volume of the 15 January 2022 eruption of Hunga volcano estimated from ocean color changes

Abstract

Abstract On 15 January 2022, Hunga volcano erupted, creating an extensive and high-reaching umbrella cloud over the open ocean, hindering traditional isopach mapping and fallout volume estimation. In MODIS satellite imagery, ocean surface water was discolored around Hunga following the eruption, which we attribute to ash fallout from the umbrella cloud. By relating intensity of ocean discoloration to fall deposit thicknesses in the Kingdom of Tonga, we develop a methodology for estimating airfall volume over the open ocean. Ash thickness measurements from 41 locations are used to fit a linear relationship between ash thickness and ocean reflectance. This produces an airfall volume estimate of ~ 1.7 km3. The whole eruption produced > 10 km3 of pyroclastic units on the sea floor. Our fall estimates suggest that these must be dominated by gravity current deposits. This new ocean-discoloration method provides an airfall volume estimate consistent with other independent measures of the plume and is thus effective for rapidly estimating fallout volumes in future eruptions of volcanoes over oceans.