Abstract
The emplacement of lava, a multiphase fluid, is complicated by variables both intrinsic (e.g., rheology) and extrinsic (e.g., effusion rate) to the flow. Lava flows represent a hazard to populations and infrastructure proximal to volcanoes. Knowing the emplacement conditions of lava flows is important for understanding historical eruptions on Earth as well as the surface evolution of other planets (e.g., Mars or Venus) where evidence of volcanism is extensive but historical context is nonexistent. Laboratory analog experiments allow for the observation of complex flow dynamics and phenomenology observed in active flows. Here, we utilized analog experiments to investigate how changes in flow rate (via unsteady vent conditions) impact flow propagation with respect to breakouts, inflation, and tube formation. We performed 150 experiments using 2 different eruption rate patterns to address the following controls on lava flow emplacement: single step-wise decrease or increase of eruption rates on a flat slope (n=120) and double step-wise decrease-increase and increase-decrease on a flat slope (n=30). We controlled wax and ambient temperature, pulse duration, and eruption rate. Results indicate that the likelihood and magnitude of breakouts, inflation, and tubes increases with longer durations of decreasing and/or increasing eruption rates. Prolonged increases in eruption rate favor widespread marginal breakouts, surface breakouts (resurfacing), inflation, and some tube formation. Prolonged decreases in eruption rate promotes localized marginal breakouts, inflation, and tube formation. Similar observations were made during the early stages of the 2021 Fagradalsfjall eruption in Iceland. Morphologies observed in the lab were controlled by the existence, or lack of, of a coherent crust. Complex effusion rate patterns created more complex flow morphologies and surface textures not unlike those observed in nature. Post-emplacement morphologies are modified by a variety of factors (e.g., deflation), which may not preserve the finer surface textures.