The 2021 Tajogaite eruption of Cumbre Vieja (La Palma, Spain) was typified by the emission of low viscosity lavas that flowed at high velocities and inundated a large area. We experimentally investigated the rheological evolution of melt feeding the eruption through concentric cylinder viscometry to understand the exceptional flowing ability of these lavas and constrain its emplacement dynamics. We conducted a set of cooling deformation experiments at different cooling rates (from 0.1 to 10 °C/min), and isothermal deformation experiments at subliquidus dwell temperatures between 1225 and 1175°C. All experiments were conducted at a shear rate of 10 s ⁻¹ . Results show that disequilibrium crystallization and its timescale fundamentally control the rheological evolution of the melt, resulting in different rheological response to deformation of the crystal‐bearing magmatic suspension. Integrating rheological data with field observations allows us to shed light on the mechanisms that govern the high flowability of these lavas.