Meghann F.I. Decker | Search USGS

USGS2026

Spatial and temporal geochemical variations of lava flows and tephra deposits from the December 2020 to September 2024 eruptions of Kīlauea volcano

Kīlauea volcano underwent dramatic morphological changes in 2018. That year recorded the end of the 35-year-long eruption of Puʻuʻōʻō (1983–2018) and 10-year-long (2008–2018) Halemaʻumaʻu lava lake and emplacement of the ~4-month-long lower East Rift Zone lava flows that coincided with ~500 m of summit caldera collapse. Starting on December 20, 2020, eruptions resumed at Kīlauea’s summit. There were five summit eruptions between December 2020 and September 2023, which ranged in duration from more than a year to as short as a week. Following these summit eruptions, seismicity and deformation increased in the upper Southwest Rift Zone in 2024, culminating in a ~8.5-h-long eruption in this region on June 3, 2024. Increased seismicity and deformation then shifted to the upper and middle East Rift Zone and after several months culminated in an eruption just west of, and within, Nāpau Crater in the middle East Rift Zone from September 15 to 20, 2024. Despite vast morphological changes at Kīlauea’s summit, the geochemical compositions (i.e., whole rock and glass) that erupted from December 2020 to September 2023 are all remarkably similar to each other. Whole-rock compositions appear distinct from the preceding 2008–2018 Halemaʻumaʻu lava lake and phase 3 (i.e., summit or uprift-derived mafic lavas) of the 2018 lower East Rift Zone lava flows, although glass compositions appear to have more overlap with 2018 lower East Rift Zone glasses. The June 3, 2024, upper Southwest Rift Zone spatter and lava flows exhibit a dramatic enrichment in whole-rock MgO that is not recorded in glass, which reflects accumulation of olivine (e.g., antecrysts or xenocrysts) during dike emplacement, and is consistent with the abundance of olivine in the lava flows (5–10%). June 2024 Southwest Rift Zone whole-rock and glass compositions overlap with those erupted at the summit from December 2020 to September 2023, whereas some whole-rock trace (i.e., Sc, Sr, and Zr) and major elements (i.e., CaO) are suggestive of mixing with a magmatic component that had fractionated plagioclase and pyroxene and/or a new parental magma influencing the summit reservoir system. The September 15–20, 2024, eruption at Nāpau Crater in the middle East Rift Zone involved the most differentiated magma since eruptive activity resumed in December 2020, with its magma fractionating olivine + plagioclase + pyroxene. The September 15–20, 2024, composition resembles Puʻuʻōʻō lava flows that erupted in, or near, Nāpau Crater in 1983 (episode 1), 1997 (episode 54), and 2011 (episode 59), with episode 59 having a compositional cluster that is most similar to that of the September 2024 lava flows. The data presented and provided herein open new research perspectives for long-term analyses of geochemical variations following caldera collapse at Kīlauea volcano and facilitate comparisons with other basaltic caldera systems worldwide.

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USGS2026

Petrologic and geochemical characterization of the first year of the 2024–ongoing episodic Halemaumau eruption of Kilauea (Episodes 1–39)

Kīlauea has been erupting episodically since December 23, 2024 (and is ongoing at the time of this writing in 2026) with two consistently active vents in Halema‘uma‘u producing lava fountains ranging in height from 40 to 540 m. In the first year of the eruption (through December 24, 2025, episode 39), the U.S. Geological Survey's Hawaiian Volcano Observatory collected 178 samples for eruption monitoring purposes and used a subset of 80 for near-real-time geochemical analyses. Tephra, lava, and recycled lava lake ooze-out samples have been studied on inter-episode timescales using diverse microanalytical techniques, where research-scale investigations have proven to be advantageous pseudo-near-real-time techniques. Here we present a geochemical and petrologic overview of episodes 1–39 to better understand eruption dynamics and identify changes at Kīlauea following the 2018 summit caldera collapse. There are no significant intra-episode geochemical changes that might be related to variable fountain heights or episode durations, suggesting that eruption dynamics are instead primarily controlled by viscosity and conduit geometry changes throughout a single episode and between episodes. There is variable but clear influence of the still-molten lava lake interior on compositions of this eruption, including in tephra samples from lava fountains, indicating that the vent conduits are connected in some way at depth with the still molten passive lava lake core. Tephra glasses (7.0–7.8 wt.% MgO) show cyclic changes in MgO that were decoupled from lava fountain heights and behavior in episodes 1–28 but positively correlated after episode 29. Additionally, whole-rock and glass compositions are enriched in minor elements such as K 2 O and TiO 2 compared to 2008–2023 summit eruptions, tracking the arrival of a new magma composition that may be related to the prolonged episodic eruptive behavior. Olivine-hosted melt inclusions from five episodes have ~0.35–0.43 wt.% H2O, < 300 ppm CO 2 and < 1500 ppm S, with no significant variations between episodes. Melt and fluid inclusion barometry show that magmas driving these episodes are stored and sourced from the shallow 1–2 km Halemaʻumaʻu reservoir, as were olivine from the 2023 summit eruption. The ongoing episodic eruption also has higher bulk-rock MgO compared to the five previous summit eruptions (2020−2023) and the forsterite (Fo) content of olivine has varied systematically from 2015 to 2025 with the equilibrium olivine composition of the Halema‘uma‘u reservoir increasing from Fo 80.7 in 2015 to Fo 82.7 by 2025. We argue that the Halemaʻumaʻu reservoir is heating up because the rate of magma supply is outpacing effusion and cooling following caldera collapse in 2018.

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