This 2D side-view simulator models a lava flow as a Bingham-plastic viscous gravity current descending a slope from a vent at the left edge. The flow's advance is governed by the real analytic flux law for a Bingham fluid on an incline, including the critical yield thickness below which lava simply cannot move. Raise the effusion rate to feed the flow faster, dial up melt viscosity to thicken and slow it, and steepen the slope to speed its descent. As the surface cools it darkens into a solidifying crust that raises the local yield stress and viscosity until the front finally jams — watch the live readouts track front distance, speed, effective viscosity and crust coverage as the eruption plays out.