Sensitivity of mean vertical fluid velocity w to dike width under SP conditions for a range of dynamic viscosities. Panel (a): turbulent and laminar flow are indicated by solid and dashed–dotted lines, respectively. Dike widths less than the critical value required for sustained flow are indicated by the “complete solidification” field. Panel (b): corresponding volumetric flow rates Q assuming the dike breadth is 1000 times its width. Complete solidification of conduit fluid occurs when flow rates are less than 25 m³ s⁻¹.