I mined into it
1) You dug forward but didn't run away.
2) You dug straight down. Self explanatory.
3) You blindly walked forward without taking a glance and being careful.
4) You mined upwards into the ceiling. This requires a complicated technique of sorts to protect yourself from this without blocking the source of lava, leading me to my fifth possible action:
5) You didn't block the lava. Or you didn't have anything to block it.
Take your pick. C: