RHEOLOGY OF THE ANDESITE ERUPTED FROM FISSURE 17 OF THE 2018 KILAUEA LOWER EAST RIFT ZONE ERUPTION

In 2018, basaltic lava erupted on the Lower East Rift Zone (LERZ) of Kilauea, Hawaii. Of the 24 identified vents, 23 erupted basalt, while one produced lava with a bulk andesitic composition. This complex lava is fissure 17 which was active from May 13-25 of 2018. We collected 5 samples of fissure 17 lavas. These rocks contain both microlites and coarse-grained phenocrysts of plagioclase, two pyroxenes, and no olivine. Mixing of two different lavas is visible on a centimeter-scale, with a glassy trachytic fine-grained matrix; the other with a dark cryptocrystalline matrix, large rounded vesicles, and large euhedral crystals of plagioclase. This has been interpreted as resulting from fresh basaltic lava encountering a cool crystal-rich mush pocket from a previous magmatic episode. The petrology, density, rheology, and thermal properties of fissure 17 lavas will be further investigated, and compared with the voluminous fissure 8 eruption, to better understand the variety of physical properties and behaviors that can be exhibited by lava flows erupted within a single fissure zone eruption at Kilauea. The viscosity of the lava will be measured using both uniaxial compression (parallel-plate viscometry) and oscillatory shear (dynamic mechanical analysis, DMA). Compared to the hotter, less crystal-rich lava that is fissure 8, our preliminary hypothesis is that lava viscosity at fissure 17 is higher due the higher crystal content, and lower eruption temperature - both consequences of mingling with the cooler crystal-rich mush pocket prior to eruption.