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#           Olivine diffusion constrains months-scale magma transport within Kīlauea volcano’s summit reservoir system prior to the 2020 eruption      

      March 8, 2024    

The unprecedented 2018 summit collapse at Kīlauea and subsequent 2020–2021 eruption within the newly deepened Halema‘uma‘u Crater provide an unparalleled opportunity to understand how collapse events impact a volcano’s shallow reservoir system and magmatic processes. Glass and olivine from tephra ejected by lava fountains and several explosions on 20–21 December, within a few hours of the 2020 eruption onset, yield information about pre-eruptive magma storage and transport. The olivine population is bimodal with zoned and non-zoned phenocrysts. Normally zoned olivine crystals with core compositions around Fo88 have 30–50 μm wide Fo82 overgrowth rims that have skeletal textures. Two skeletal xenocrysts (cores Fo74 and Fo81) are also reversely zoned up to Fo82 rims. The crystal cores have trace element records of at least two cycles of growth and dissolution prior to the formation of the overgrowth rims. These rims and a separate population of non-zoned Fo82 crystals are in Fe–Mg equilibrium with their host glass (average MgO of 6.9 ± 0.4 wt% (1σ), Mg# [Mg / (Mg + Fe2+)] of 0.57), which suggests undercooling after intrusion of magma to shallow levels in the plumbing system. In the years prior to the 2018 collapse, non-zoned Fo81 olivine and slightly lower MgO glasses (6.8 wt%) reflected continuous mixing and compositional buffering of magma recharge into several km3 of stored magma in the Halema‘uma‘u reservoir (1–2 km depth). The 2020 olivine crystals lack evidence of an intrusion mixing with resident shallow magma, indicating that magma transport occurred in a disrupted system, and/or it may not have significantly mixed with stored magma remaining in the Halema‘uma‘u reservoir after the events of 2018. Diffusion modeling of Fe–Mg exchange in the zoned 2020 olivine crystals yield timescales that are mostly 60 days prior to the eruption or less, which aligns well with 22–24 October 2020 and subsequent seismic swarms at Nāmakani Paio ~ 5 km west of Kīlauea’s summit caldera. This correlation indicates that magma intruding beneath the summit (volume accommodation, recorded by the olivine crystals) was expressed by tectonic earthquakes along the Ka‘ōiki fault zone (stress accommodation). The absence of precursory SO2 within minutes prior to eruption also indicates that the 2020 December magma may have risen from 1 to 2 km depth to the surface in as little as 10 min.

## Citation Information

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#### Kendra J. Lynn, Ph.D.

##### Volcanologist - Petrologist

Hawaiian Volcano Observatory

klynn@usgs.gov

808-967-8844

#### Patricia A. Nadeau

##### Volcanologist

Hawaiian Volcano Observatory

pnadeau@usgs.gov

808-967-7328

#### Dawn C.S. Ruth, PhD

##### Volcanologist and Electron Microbeam Lab Manager

California Volcano Observatory

druth@usgs.gov

650-329-4935

#### Jefferson C Chang, Ph.D.

##### Geophysicist

Hawaiian Volcano Observatory

jchang@usgs.gov

808-967-8818

#### Ingrid A. Johanson

##### Research Geophysicist

Hawaiian Volcano Observatory

ijohanson@usgs.gov

808-967-8838

## Related Content

#### Kendra J. Lynn, Ph.D.

##### Volcanologist - Petrologist

Hawaiian Volcano Observatory

klynn@usgs.gov

808-967-8844

#### Patricia A. Nadeau

##### Volcanologist

Hawaiian Volcano Observatory

pnadeau@usgs.gov

808-967-7328

#### Dawn C.S. Ruth, PhD

##### Volcanologist and Electron Microbeam Lab Manager

California Volcano Observatory

druth@usgs.gov

650-329-4935

#### Jefferson C Chang, Ph.D.

##### Geophysicist

Hawaiian Volcano Observatory

jchang@usgs.gov

808-967-8818

#### Ingrid A. Johanson

##### Research Geophysicist

Hawaiian Volcano Observatory

ijohanson@usgs.gov

808-967-8838

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