Not sure if someone has had this same experience or posted it so apologies if so.
So I was boiling my yeast starter wort in a erlenmeyer flask directly on my stove and realized it was boiling very rough (less bubbles, more explosive and popping than normal) I realized this was due to a lack of surface impurities in the glass flask for vapor bubbles to form on but I couldn't figure out why it didn't do this during previous boils.
Well I realized that I forgot to add yeast nutrient to the mix so I decided to add it mid boil and learned the hard way. The boil immediately exploded, spewing out the neck of the flask like a science project volcano (except dangerously hot!!).
I immediately realized that adding the nutrient powder provided thousands of little points (or nucleation sites) for the vapor bubbles to form on thus creating an instant boilover. Without good nucleation sites, water has difficulty boiling and will become superheated (above normal boiling temp). Adding nucleation sites at this point will result in a huge and potentially dangerous release of the superheated energy in the form of vapor bubbles.
moral of the story: Be careful adding stuff to boils that may be superheated! Usually glass, pyrex, or ceramics would be culprits for this. Also, the yeast nutrient seemed to make for a smoother boil once everything settled back down to normal. Just add it at the beggining