Abstract—Volcanic eruptions belong to the extreme events that change the Earth’s landscape and affect global climate and environment. Although special attention is given to super-eruptions, the non-explosive rhyolitic (highly viscous) eruptions and large lava flows are no less important. In this paper, we study an ancient lava flow with a volume of ~50 km3 in the Summit Lake region, Yellowstone, which is one of the best studied large intraplate igneous provinces. We develop three-dimensional (3D) numerical models of isothermal lava flow to analyze the influence of the underlying surface and lava flow viscosity on the advancement and duration of the flow. The modeled dynamics of flow propagation fairly well agrees with the measured values provided that the average angle of inclination of the underlying surface slightly differs from the present-day value (by ~1.3°) presumably due to the pressure change in the magma chamber during the eruption. With the increase in lava viscosity, the flow slows down and its thickness increases leading to a change in the flow morphology.