LAUSR

Abstract Kīlauea's Pu‘u ‘Ō‘ō eruption was the longest lived (35+ years), and most voluminous (~4.4 km3) and intensely monitored historical eruption of this Hawaiian volcano. A synthesis and update are presented here on the remarkable petrologic and geochemical evolution of lava erupted from its inception on 03 Jan. 1983 to its demise on 01 May 2018. This time-series analysis chronicled mantle and crustal processes that varied during this eruption, which had more than a two-fold lava effusion rate increase. Our frequent sampling of Pu‘u ‘Ō‘ō lava allowed the changes in crustal and mantle process during this single magmatic event to be assessed. New major element, trace element, and Sr isotope data are presented here for the period from 2010 to 2018. These results are combined with our previous geochemical studies to reveal the complex interplay of crustal processes that dominated the eruption's first 500 days. Subsequently, mantle geochemical signatures became discernible as the crustal-stored magma was flushed from the conduit system and replace by new mantle-derived magma. This flushing was possible because of the relatively small size of the summit magma reservoir system compared to the volume of magma erupted at Pu‘u ‘Ō‘ō (≤0.2 vs. 4.4 km3). Parental magma compositions changed rapidly during the eruptionreflecting source heterogeneity in the mantle plume. The depth of melt segregation may have also changed during the eruption. These results demonstrate the importance of systematic temporal sampling during an active eruption.