The 15 January 2022 shallow water eruption of Hunga Tonga-Hunga Ha’apai (HTHH) volcano was remarkable, in part, because it produced the highest plume observed in the advanced satellite era. The Himawari-8 geostationary satellite captured this HTHH eruption well and provides a unique opportunity to track the evolution (plume and umbrella cloud height) of a large volcanic eruption through time. The 15 January 2022 eruption was preceded by eruptions in late December 2021 and 13 January 2022, for which we have also assessed plume characteristics. In addition to umbrella cloud height, we use Himawari-8 data to determine the radial expansion of the umbrella clouds and volumetric flow rates (VFR). The altitude of umbrella clouds preceding 15 January 2022 reached ~16-18 km, crossing into the stratosphere. On the day of the large climactic eruption (15 January 2022), the umbrella clouds attained a height close to 31 km. We observed two powerful explosive eruptions on 15 January at an interval of four hours, indicated by the minimum 11.2μm brightness temperature occurring at 04:10 UTC (172 K) and 08:10 UTC (174 K). On 15 January 2022, beyond 05:30 UTC, the strong westward propagation of upper umbrella (UB) clouds at ~31 km enabled the visibility of lower umbrella (UA) clouds at ~18 km. We find that UA is mainly dominant with ash, whereas UB is dominant with thick ice clouds based on brightness temperature difference analysis. The satellite-derived VFR for 15 January 2022 is around 5.00 x 10^11 m3s-1, nearly two orders of magnitude higher than that estimated on 19 December 2021 and 13 January 2022 eruptions.

The August 12, 2021 eruption of Fukutoku-Okanoba, a shallow submarine volcano in the Izu-Bonin arc of Japan, is one of few documented submarine eruptions to make a large aerial plume and floating pumice raft. Relative to past eruptions, this event was well-covered by multiple high resolution satellite remote sensors. Here we use satellite remote sensing to assess the eruption style, rates, and products. We find that the 16 km plume was water-rich. Furthermore, we conclude that the 0.1 km^3 raft and 16 km plume were co-genetic and suggest that pumice clasts were delivered to the raft by tephra jets rather than plume fallout. Finally, this eruption highlights a discrepancy between small erupted volumes and high plume heights that may be common for shallow explosive subaqueous eruptions.

Most of Earth’s volcanic eruptions occur underwater, and these submarine eruptions can significantly impact large-scale earth systems. In this study, we develop a new semi-automated analysis framework to detect submarine eruptions through the supervised classification of satellite images on Google Earth Engine (GEE). We present a case study from the Rabaul caldera region in Papua New Guinea and find a large number of new unreported pumice rafts (in ~16% of images from 2017–present). After analysis of the spatial pattern of raft sightings and ancillary observations, we interpret that these rafts are not the result of a new eruption. Instead, we posit that the observed rafts represent remobilization of pumice clasts from previous historical eruptions. This novel process of raft remobilization may be common at near-shore/partially submarine caldera systems (e.g., Rabaul, Krakatau) and has significant implications for new submarine eruption detection, volcanic stratigraphy, and biological dispersal by rafts.