School of Ocean and Earth Science and Technology, University of Hawaii, Manoa, Honolulu, HI, 96822, USA.
School of Ocean and Earth Science and Technology, Hawaii Institute of Geophysics and Planetology, University of Hawaii, Manoa, Honolulu, HI, 96822, USA.
Sci Rep. 2019 Aug 14;9(1):11860. doi: 10.1038/s41598-019-48268-0.
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 He/He 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 He/He 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 He/He 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 He relative to their He/He ratio, similar to previous findings there and suggestive of a previously unknown He isotopic fractionation.
2018 年 5 月 1 日，基拉韦厄火山中东部裂谷带（ERZ）上的 Pu'u O'o 火山口发生 5.0 级地震，该火山自 1983 年以来一直活跃。从 2018 年 4 月 30 日到 5 月 2 日，记录到 ERZ 中到下部地震活动增加。Pu'u O'o 火山口和 Halema'uma'u 火山口内的活跃熔岩湖开始排空，山顶火山口开始放气，山顶坍塌于 2018 年 8 月 2 日结束，ERZ 下部喷发熔岩活动于 2018 年 9 月 4 日结束。在此，我们报告了 2017 年 9 月初采集的下部 ERZ 蒸汽喷口中升高的 He/He 比值。使用一种新的、现场便携式 He 同位素探测器进行气体同位素测量，该探测器能够进行每日次的 He/He 比值监测。当校正空气污染后，这些值比基拉韦厄以前报告的值高出近两倍，类似于更纯净的热点羽流特征，例如在夏威夷岛东南的 Loihi 海山的地幔羽流上直接测量到的特征，以及在基拉韦厄和其姊妹夏威夷盾状火山位于羽流上方时测量到的较老玄武岩流中的特征。这一发现预示着在该地区喷发提前了八个多月，这表明我们要么采样了下部 ERZ 中已经存在的富含 He 的岩浆，要么采样了下部 ERZ（普纳区）中浅层地下水储层，其 He 含量相对于 He/He 比值异常低，类似于以前在那里的发现，并暗示了以前未知的 He 同位素分馏。
