Liquid Dam: A Constant-Speed Regime in Gravity-Driven Shear-Thickening Suspensions

Shear-thickening suspensions-materials that abruptly become more viscous or jam under stress-are widespread in nature and industry. Yet their dynamics in gravity-driven flows remain poorly understood. Here, we show that such suspensions spread by forming a sharp, vertical front-a liquid dam-that advances at a constant speed, independent of released volume, flow height, and slope. This counterintuitive behavior arises from a jammed, frictional front that localizes dissipation and decouples flow dynamics from geometry. A simple gravito-rheological model predicts the observed constant-speed regime, with a velocity scale set by the suspension rheology. The same scaling governs spreading and wave propagation across diverse flow configurations, revealing how shear thickening can critically shape gravity-driven flows in both natural and industrial settings.