Comprehensive characterization of Mauna Loa basalt rheology based on the 2022 eruption

Rheological data are crucial for the understanding of storage, transport, eruption, and emplacement of magma and lava. While viscosity estimates for lavas from Mauna Loa, the largest active volcano on Earth, exist, no direct rheological measurements have been done to date. This is especially surprising given the role Mauna Loa lavas and resulting landforms play in the interpretation of volcanic processes across our solar system and beyond. We present the first complete rheological characterization of Mauna Loa lava, based on the 2022 eruption. We constrain the melt viscosity and map the lava's rheology during crystallization at isothermal subliquidus conditions and at cooling at rates between 0.25 and 3.00 °C/minute. These experiments were performed at oxygen fugacities relevant to storage and eruption conditions at Mauna Loa (log fO₂ = -8.7). We integrate textural and thermal characteristics obtained from the experiments with those from water quenched natural samples (i.e. sampled from actively flowing lava and quenched within seconds to preserve the textural state of the lava while flowing) to reconstruct the evolution of lava rheology during emplacement. This integration suggests that the Mauna Loa lavas were emplaced at viscosities between 10^1.5 to 10^4.5 Pa s over the temperature range of 1150 – 1090 °C before entering a region of rapid viscosity increase and effective solidification caused by groundmass crystallization. We provide a detailed comparison of our data to rheological reconstructions of the 1984 eruption. The resulting rheological map can help guide physical property-based magma ascent and lava emplacement models, as well as the interpretation of flow morphologies and the conditions of formation of basaltic landforms on other planets.