281-10 How Lava Flows as it Cools: Rheology Insights from Disequilibrium Two-step Cooling Deformation Experiments

Session: Petrology, Volcanology, and Mantle Plumes across the Solar System, Part II

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This work investigates the impact of two-step cooling rates on the evolution of melt viscosity, revealing how rheological memory impacts a lava’s ability to flow. Lava flows cool through radiative, convective, and conductive heat loss, each acting in varying measures at different stages of emplacement and thus affecting different parts of the flow. A concentric cylinder rheometer can be used to perform cooling deformation experiments (CDEs) that allow lava to cool dynamically; however, previous CDEs used simple, one-step rates that do not replicate natural transitions in cooling conditions. This study closes that gap by applying two-step cooling protocols with a constant shear rate of 1 s^-1. Our two-step CDEs simulated 1) lava channel cooling conditions, transitioning from fast to slow (1 to 0.5, 2 to 0.5, 3 to 0.5, 4 to 0.5, and 5 to 0.5 °C/min) and 2) lava tube to breakout conditions, transitioning from slow to fast (0.5 to 1, 0.5 to 2, 0.5 to 3, 0.5 to 4, and 0.5 to 5 °C/min). The transition temperature for both sets of CDEs occurred at 1165 °C, the midway point between the liquidus (1190 °C) and the average viscosity cutoff observed in the one-step CDEs from previous work on the sample used in these experiments. Results from the novel channel-like two-step CDEs followed the trend of one-step CDEs initially, then steepened upon switching to the 0.5 °C/min rate, reaching higher viscosities at higher temperatures than the equivalent one-step cases. The tube-like two-step CDEs reached lower temperatures than the channel-like two-step CDEs and reached generally lower peak viscosities, with viscous rupture depending on the secondary cooling rate. Additionally, when comparing all one-step and two-step CDEs results at a common temperature (1132 °C), the two-step 5 to 0.5 (196 Pa s) and 0.5 to 5 °C/min (207 Pa s) CDEs are over 50% less viscous than the one-step 0.5 °C/min CDE (417 Pa s). These findings exemplify how thermal history controls the viscous evolution and rupture behavior of basaltic lava flows, offering more realistic insights into lava flow dynamics.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-5918

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