A novel phenomenon of quasi-volcanic corrosion at refractory-slag-air interface under simulated normal smelting conditions was discovered when alumina refractory came in contact with CaO-Al2O3-SiO(2)slags and soaked at 1600 degrees C. Based on thermodynamic and microstructure analysis, the mechanism of quasi-volcanic corrosion was revealed and the effect of CaO/SiO(2)mass ratio (C/S ratio) on corrosion was discussed. The results indicate that a two-stage intensified convection led to the severe upwelling corrosion of the refractory at the triple-phase interface. Furthermore, the critical intensity of the corrosive convection at the first stage on the formation of "slag volcano" was determined. This can serve as guidance for prolonging the service life of alumina refractory.