Sulfur dioxide emission rates from Hawaiian volcanoes, 2018-2022

Measurement of sulfur dioxide (SO2) emission rates is a critical aspect of monitoring and studying active volcanoes. Changes in emission rate are often associated with changes in volcanic activity and in some cases may herald future changes in activity. At the Hawaiian Volcano Observatory (HVO), emission rates of SO2 from Hawaiian volcanoes have been measured by ultraviolet spectrometer since the late 1970s [Casadevall and others, 1987]. Here we present a compilation of SO2 emission rate measurements made from 2018 to 2022. The emission rates (in t/d) span five orders of magnitude through a range of activity styles unprecedented in recent times, including caldera collapse [Anderson and others, 2019], the first prolonged non-eruptive period at Kīlauea since the early 1980s, a summit water lake [Nadeau and others, 2020], and the first eruption of Mauna Loa in nearly 40 years.

At Kīlauea, emission rates were relatively steady early in 2018, at both the summit, where a lava lake had existed for the past decade [Patrick and others, 2021], and middle East Rift Zone (MERZ), where Puʻuʻōʻō had been in a state of near-constant eruption for 35 years [Orr and others, 2015]. The 2018 lower East Rift Zone (LERZ) eruption and concurrent summit caldera collapse [Neal and others, 2019] between May and September 2018 brought with them unprecedented high SO2 emission rates at the LERZ eruptive fissures and temporary increases in SO2 emissions at both the summit and Puʻuʻōʻō [Kern and others, 2020a]. By the end of the eruption in late summer of 2018, emissions at all three sites had dropped drastically, including to below-detection and near-negligible at the LERZ and MERZ sites, respectively [Kern and others, 2020a]. During 2019 and 2020, emissions on the MERZ also decreased to below-detection limits, and even Kīlauea summit emission rates were down to near detection levels. 2019 also saw the appearance of the first summit water lake in Kīlauea’s crater in written history (though Hawaiian oral tradition alludes to possible water bodies in the crater in the past [Swanson, 2008], which is also supported by analysis of erupted material from explosive eruptions in the 16th through 18th centuries [Mastin, 1997; Swanson and others, 2012; Swanson and Houghton, 2019]). The extremely low SO2 emissions from the summit during 2019 and 2020 raised the question of possible scrubbing of SO2 by the lake, though that was ultimately determined to not be a significant contributing factor [Nadeau and others, 2023]. High SO2 emissions returned to Kīlauea late in December of 2020 when lava erupted from the walls of the summit crater, boiled away the lake, and filled the crater with a new lava lake [Cahalan and others, 2023]. SO2 emissions decreased as the eruption progressed and eventually returned to low, background levels during mid-2021 when the eruption ceased. Another Kīlauea summit eruption initiated in September of 2021, bringing with it a return to high SO2 emission rates. The 2021 eruptive activity continued through much of 2022, including a period of brief pauses, during which SO2 emissions dropped to near-background levels for a short time, after which they increased again with the cessation of the pause and the return of lava to the summit crater.

Just before the end of the 2021–2022 eruption of Kīlauea in late 2022, Mauna Loa erupted for the first time since 1984. The eruption initiated in the summit caldera and migrated within hours to a set of fissures on the Northeast Rift Zone (NERZ). SO2 emission rates from Mauna Loa reached very high levels similar to those of the 2018 Kīlauea LERZ activity. The Mauna Loa eruption was shorter than Kīlauea’s 2018 LERZ eruption, however, with eruptive activity ceasing and SO2 emission rates returning to below-detection only two weeks after the eruption began.

In this data release, we include raw spectra collected by ultraviolet (UV) spectrometers on traverses beneath SO2 plumes, derived SO2 emission rates and associated metadata for each individual traverse, and means of SO2 emission rates for each separate traverse campaign/set of traverses. Data are separated by the four eruption sites/degassing locations: Kīlauea summit (Halemaʻumaʻu), Kīlauea MERZ (Puʻuʻōʻō), Kīlauea LERZ, and Mauna Loa NERZ.

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