Out of the blue: Volcanic SO2 emissions during the 2021–2022 eruptions of Hunga Tonga—Hunga Ha’apai (Tonga)

Abstract

Most volcanism on Earth is submarine, but volcanic gas emissions by submarine eruptions are rarely observed and hence largely unquantified. On 15 January 2022 a submarine eruption of Hunga Tonga-Hunga Ha’apai (HTHH) volcano (Tonga) generated an explosion of historic magnitude, and was preceded by ∼1 month of Surtseyan eruptive activity and two precursory explosive eruptions. We present an analysis of ultraviolet (UV) satellite measurements of volcanic sulfur dioxide (SO2) between December 2021 and the climactic 15 January 2022 eruption, comprising an unprecedented record of Surtseyan eruptive emissions. UV measurements from the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite, the Ozone Mapping and Profiler Suite (OMPS) on Suomi-NPP, the Tropospheric Monitoring Instrument (TROPOMI) on ESA’s Sentinel-5P, and the Earth Polychromatic Imaging Camera (EPIC) aboard the Deep Space Climate Observatory (DSCOVR) are combined to yield a consistent multi-sensor record of eruptive degassing. We estimate SO2 emissions during the eruption’s key phases: the initial 19 December 2021 eruption (∼0.01 Tg SO2); continuous SO2 emissions from 20 December 2021—early January 2022 (∼0.12 Tg SO2); the 13 January 2022 stratospheric eruption (0.06 Tg SO2); and the paroxysmal 15 January 2022 eruption (∼0.4–0.5 Tg SO2); yielding a total SO2 emission of ∼0.6–0.7 Tg SO2 for the eruptive episode. We interpret the vigorous SO2 emissions observed prior to the January 2022 eruptions, which were significantly higher than measured in the 2009 and 2014 HTHH eruptions, as strong evidence for a rejuvenated magmatic system. High cadence DSCOVR/EPIC SO2 imagery permits the first UV-based analysis of umbrella cloud spreading and volume flux in the 13 January 2022 eruption, and also tracks early dispersion of the stratospheric SO2 cloud injected on January 15. The ∼0.4–0.5 Tg SO2 discharged by the paroxysmal 15 January 2022 HTHH eruption is low relative to other eruptions of similar magnitude, and a review of other submarine eruptions in the satellite era indicates that modest SO2 yields may be characteristic of submarine volcanism, with the emissions and atmospheric impacts likely dominated by water vapor. The origin of the low SO2 loading awaits further investigation but scrubbing of SO2 in the water-rich eruption plumes and rapid conversion to sulfate aerosol are plausible, given the exceptional water emission by the 15 January 2022 HTHH eruption.

The unexpected radiative impact of the Hunga Tonga eruption of 15th January 2022

“…The underwater HT eruption injected a huge amount of water vapour into the stratosphere, with an estimated amount exceeding 100 Tg 10,17 . These water vapour emissions are unprecedented in the satellite era; nevertheless, estimates with petrological methods indicate that large eruptions of the past, including the one of Pinatubo in 1991, may have produced even significantly larger water vapour emissions 11 . The large HT water vapour emissions are likely due to both volcanic caldera intrusion of seawater and mechanical interaction with seawater, over the underwater eruptive crater, during the eruption.…”

“…Volcanic ash, gas and water vapour were injected well into the stratosphere, with a small part of the plume reaching the lower mesosphere 10 . Although the explosivity of the eruption was unprecedented, best estimates from different satellite instruments are consistent in measuring a total burden of the injected sulphur dioxide (SO 2 ) of about 0.4 Tg 11 . This is far less than the injected mass for the large magnitude Pinatubo eruption (Philippines, 1991), which emitted 14 to 23 Tg of SO 2 12 , or even the more recent moderate stratospheric Raikoke 2019 (1.5 ± 0.2 Tg 13 ) or Nabro 2011 eruptions (1.6 Tg 14 ).…”

Global perturbation of stratospheric water and aerosol burden by Hunga eruption

“…The presence of large amounts of water in the volcanic plume has probably led to very fast oxidation of volcanic sulfur dioxide emissions to sulfuric acid-the main component of stratospheric aerosol droplets 31,32 . Another potential factor of expedited SO 2 conversion to aerosols could be heterogeneous oxidation of SO 2 on the surface of ash 31,33 .…”

“…The extreme explosiveness of the Hunga eruption and the submarine location of the volcano add up to the unprecedented character, magnitude and the propagation timescale of the global stratospheric perturbation 20,22,24,31,32,34,50 . The eruption provided a unique natural testbed, lending itself to studies of climate sensitivity to strong change in both stratospheric gaseous and particulate composition.…”

The evolution and dynamics of the Hunga Tonga–Hunga Ha'apai sulfate aerosol plume in the stratosphere

“…A further remarkable fact is that the plume carried an unprecedented amount of water vapour into the stratosphere, increasing instantaneously its overall water vapour content by ∼ 10 % (Millán et al, 2022;Khaykin et al, 2022). Quite surprisingly, the satellite data gathered after the event reported a stratospheric SO 2 injection of only 0.5 Tg, on par with much smaller and less explosive eruptions (Millán et al, 2022;Carn et al, 2022). This led to an early estimate of negligible climatic impact (Witze, 2022;Zhang et al, 2022).…”