UC San Diego

Mauna Loa is one of Earth’s largest and most active volcanoes. With its longest repose time in recorded history of 38 years, the latest eruption of Mauna Loa took place on November 27, 2022, and lasted for ~12 days. In this thesis I report new trace- and highly siderophile-element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundance and 187Re-187Os and 18O/16O data for extruded lavas spanning the eruption period. Lavas have a limited range of MgO (6.2 ±0.4 wt.%; all uncertainties 2SD) and Ni (83 ±2 µg/g) with a broader range of Re (300 to 1300 pg/g) and Os (31 to 80 pg/g) contents. The 2022 lavas have 187Os/188Os (0.1345 to 0.1385) within the range of, or slightly more radiogenic than, Mauna Loa picrites (0.1281 to 0.1349), but similar to differentiate tholeiitic lavas (0.1340 to 0.1381). Oxygen isotope compositions of glassy samples span a range in δ18O of +5 to +5.6‰ with an average composition similar to MORB as well as the recent 2021 La Palma and 2021 Fagradalsfjall basaltic eruptions in the Canary Islands and Iceland, respectively.The 2022 Mauna Loa eruption provides significant contrast for Os isotope and HSE systematics compared with the recent, longer-lived eruptions on La Palma (Canary Islands) and the Reykjanes Ridge (Iceland) that began in 2021. Initial lavas were more fractionated for both of these comparison eruptions and had more radiogenic Os isotope compositions than later erupted products. This contrasts with 2022 Mauna Loa, where no such trends are observed. Studies of the plumbing system beneath Mauna Loa and the island of Hawai’i indicate an intricate and large-scale ‘web’ of magma transit pathways beneath the volcanoes. We suggest that the limited range in compositions of the erupted products at Mauna Loa and their strongly fractioned HSE patterns reflect long-term storage, crystal fractionation and pooling of magma beneath the volcano prior to eruption triggering.