The viscosity of suspensions depends not only on the liquid phase but also on the proportions of suspended solids and bubbles. Lava is a three-phase suspension containing solid crystals and volcanic gas bubbles in liquid silicate. Measurements of the viscosity (resistance to flow) of lava are typically made on the liquid only, or liquid and crystals, but conventional wisdom says that bubbles cannot be retained. We have developed a method to measure lava viscosity while retaining much of the bubble content of lava, as well as original phenocrysts. Results on lava erupted from Kīlauea volcano, Hawai'i, in 2018 indicate that bubbles strongly reduce the viscosity of lava and contribute to high flow rates and rapid emplacement.