LONG-TERM GEODETIC AND GEOCHEMICAL MONITORING OF THE LOWER EAST RIFT ZONE, KILAUEA VOLCANO, HAWAII: A FRAMEWORK FOR INTERPRETING ERUPTION BEHAVIOR OF EARLY PHASES OF THE 2018 ERUPTION

Geodetic and geochemical monitoring of the Kilauea volcano provided the basis for near real-time prediction in the rapidly changing eruptive environment of the 2018 Lower East Rift Zone (LERZ) eruption. Comparison with baseline deformation and composition allowed us to assess the emerging hazard during the volcanic crisis event.

Twenty-five years of high-precision line leveling on a dense benchmark network in the LERZ identified subtle movement on structural elements that proved to be important factors controlling fissure eruption location and style during the first two weeks of the 2018 eruption. Early stages of the eruption opened 24 short-lived fissures before Fissure 8 became dominant. Fissures 1-15 were confined to an area west of Pohoiki Rd., closely aligned with a subtle long-lived cross structure to the LERZ as determined by our annual leveling campaigns. This structure became a significant seismic and eruption barrier during the opening of eruptive fissures in the area.

Magma was emplaced in a dike that extended from Pu`u O`o to the Leilani Estates subdivision. As fissures opened in this populated area, six years of near real-time, long-term geochemical monitoring of volcanic products from Kilauea using EDXRF provided the critical background information needed to assess the evolving eruption.

We were able to correctly identify cooler rift-stored magma and identified the most evolved lava to erupt from a Hawaiian shield volcano. Early eruptions were likely triggered by dike emplacement pushing older, cooler lava to the surface. These lavas have chemical compositions consistent with older flows emplaced in the area. Our analyses show that the opening of fissure 16, to the east of the Pohoiki Rd. structure, signaled the onset of dike advancement and the eruption of hotter, less evolved magmas to the surface and had potential to flow long distances. These observations gave warning to emergency response personnel on the change in the eruption to larger flows that cascaded down the south side of Kilauea and entered the ocean. On May 23, we identified a major change in lava composition to much hotter, more fluid lava about 5 days before the catastrophic vent 8 flows began. This is significant in that it is the first time that compositional data has been integrated into eruption monitoring on a quasi-real-time basis.