How would boiling water explode?

i washed my stainless steel (7in diameter) pot with dishsoap and dried it then put 3/4 full of warm tap water in the pot and put it on the smooth top stove (no lid). It was steaming but not really boiling, then it exploded covering myself, the roof and the entire kitchen with boiling water. Leaving me with 1st and 2nd degree burns. The pot was still on the stove after with only about 1 in of water left. . (before washing the pot there was gravy that had been cooked in it, i dont know if that could make a difference) Please tell me how this could have happened!!!