The effect of bubbles on the rheology of basaltic lava flows: Insights from large-scale two-phase experiments

Abstract

Bubbles are known to have a dramatic effect on lava rheology, but their impact on lava flow run out distance has not been extensively investigated. To quantify bubble effects on basaltic lava flow emplacement, we conducted a series of large-scale two-phase (melt+bubbles) experiments at the Syracuse University Lava Project facility. In this study, nine basaltic lava flows with low to intermediate vesicle contents (approximately 3-24 vol%) were emplaced over gently sloping (4°-9°) dry sand surfaces. Their velocities were measured by particle image velocimetry, and their bulk viscosities were calculated using Jeffreys' equation. Comparison with melt-only viscosities (calculated through the GRD model) allowed the isolation of the effect of bubbles on the viscosity of the experimental flows. We find that within the investigated range of vesicularities, bubbles increase the relative viscosity of the experimental flows by up to an order of magnitude. The increase appears to be steeper for sheet flows than for lobate and toey flows. Our results, which quantitatively assess the effect of bubbles on the rheology of basaltic lava flows, will provide a basis for the refinement of models for multi-phase flows that are fundamental to accurately forecasting the emplacement of lava flows.