Leveraging geochemistry and petrology to explore the origins of explosive vs. effusive eruptive periods at Kīlauea Volcano (HI)

Abstract:

The eruptive activity of Kīlauea Volcano (Hawai‘i) in the past 2,500 years has alternated between centuries-long periods dominated either by explosive or effusive styles that may be related to top-down (crust-controlled) or bottom-up (mantle-controlled) processes.¹ Here we leverage rock and mineral chemistry from ~1500 CE to present day to elucidate the cause(s) for the effusive and explosive periods. Olivine from the historical effusive period (1823-present) are dominated by relatively evolved forsterite [Fo; Mg/(Fe+Mg)x100] contents (Fo₈₂) that reflect a steady-state crustal reservoir system where crustal storage and fractional crystallization control the composition of magmas. In contrast, olivine crystals from the explosive Keanakāko‘i Tephra (KT; ~1500-early 1800’s) and older Uēkahuna Ash (200 BCE – 1000 CE) are dominated by more primitive Fo₈₉ compositions and clear signs of magma mixing (zoned olivine, bimodal Fo populations). Glass MgO extends also to higher values (e.g.,11 wt%) during the explosive periods,² further indicating that magmas experienced minimal crustal storage. Mantle controls are more challenging to decipher. There is little correlation between eruptive style and the level of trace element enrichment in glasses, and numerous parental magmas have been inferred for each period.³ Kīlauea’s eruptive output during the KT was ~2% of the effusive period¹ and low Nb/Y (< 0.6) and La/Yb in glasses (<6.5) indicate elevated degrees of melting and/or a depleted source.³ These signatures could reflect low supply from a previously depleted source or higher supply with endogenous growth. The KT also coincides with a very active period at neighboring Mauna Loa volcano, suggesting that regional processes might also influence Kīlauea’s alternating behavior. Thus, eruptive periods are likely both mantle- and crust-controlled and may also be subject to regional factors.