High 3He/4He ratios in lower East Rift Zone steaming vents precede a new phase of Kilauea 2018 eruption by 8 months

G M Mcmurtry,E L Horn,J R Deluze,L A Dasilveira,J E Blessing

doi:10.1038/s41598-019-48268-0

Abstract

On May 1, 2018, a magnitude 5.0 earthquake heralded the collapse of the Pu’u O’o Vent on the middle East Rift Zone (ERZ) of Kilauea Volcano, active since 1983. Increased seismicity was recorded on the middle to lower ERZ from April 30 until May 2, 2018. The active lava lakes within both Pu’u O’o Vent and Halema’uma’u Crater began to drain and the summit caldera began to deflate, with the summit collapse ending on August 2, 2018 and lower ERZ eruptive lava activity ending by 4 September 2018. Herein we report on elevated 3He/4He ratios in steaming vents in the lower ERZ from samples collected in early September 2017. Gas isotopic measurements were made with a new, field-portable He isotope detector capable of sub-daily monitoring of the 3He/4He ratio. When corrected for air contamination, these values exceed those previously reported for Kilauea by nearly twofold, resembling a purer hotspot plume signature, such as those measured directly over the mantle plume at Loihi Seamount to the SE of Hawaii Island, and in older basalt flows when Kilauea and its sister Hawaiian shield volcanoes were located more directly over the plume. The discovery, which presages the eruption there by more than eight months, suggests that we either sampled a 3He/4He rich magma already in place in the lower ERZ or a shallow groundwater reservoir in the lower ERZ (Puna district) with anomalously low values of 4He relative to their 3He/4He ratio, similar to previous findings there and suggestive of a previously unknown He isotopic fractionation.

Highlights

Rift-striking cracks began to appear in roads and yards of housing subdivisions within the Puna District on April 30
Www.nature.com/scientificreports is consistent with the notion that the Hawaiian plume has undergone extensive degassing prior to incorporation into the source region of Kilauea volcano[6]. Downhole He isotopic analysis of rocks recovered from the Hawaiian Scientific Drilling Project (HSDP) drill hole indicate that in the past, sister Hawaiian shield volcanoes such as Mauna Kea and Mauna Loa possessed high and variable 3He/4He ratios when they were closer to the Hawaiian plume, showing more depleted values toward 8 Ra, the upper mantle signature characteristic of Mid-Ocean Ridge Basalt (MORB), as they moved off to the northwest[12]
Older Kilauea basalts recovered from the summit NSF drill hole show Ra values in olivine phenocrysts of up to 17.113 and those sampled at Pu’u O’o Vent to 16.4 Ra, suggesting that the magma conduit supplying the middle East Rift Zone (ERZ) is separate from that supplying the summit reservoir[14]

Summary

Introduction

Rift-striking cracks began to appear in roads and yards of housing subdivisions within the Puna District on April 30. Kilauea’s fluids are characterized by high-3He “hotspot” 3He/4He ratios of between 13.7 and 15.9 Ra6,9 These values are lower than those found on Loihi Seamount offshore of Hawaii island, with ratios up to 35 Ra9–11, which www.nature.com/scientificreports/. Is consistent with the notion that the Hawaiian plume has undergone extensive degassing prior to incorporation into the source region of Kilauea volcano[6] Downhole He isotopic analysis of rocks recovered from the Hawaiian Scientific Drilling Project (HSDP) drill hole indicate that in the past, sister Hawaiian shield volcanoes such as Mauna Kea and Mauna Loa possessed high and variable 3He/4He ratios (from 13 to 25 Ra) when they were closer to the Hawaiian plume, showing more depleted values toward 8 Ra, the upper mantle signature characteristic of Mid-Ocean Ridge Basalt (MORB), as they moved off to the northwest[12]. Older Kilauea basalts recovered from the summit NSF drill hole show Ra values in olivine phenocrysts of up to 17.113 and those sampled at Pu’u O’o Vent to 16.4 Ra, suggesting that the magma conduit supplying the middle ERZ is separate from that supplying the summit reservoir[14]

Methods

Results

Conclusion