rolling boil

Because the convection within the liquid produces strong currents that tend to swirl rapidly in circular patterns from bottom to surface and back again.

rolling boil (plural rolling boils)

1. (cooking) The boiling of a liquid rapidly with plenty of bubbling, which (unlike simmering) roils the liquid and thus may break up or alter the shape of ingredients.
   • 2022 October 17, Stuart Heritage, “Now it’s over, let’s come out and say it: The Rings of Power was a stinker”, in The Guardian‎:

     House of the Dragon has sucked up the spotlight. It has attracted tweets, theories, memes, discussions, all on a rolling boil since the first episode.

• “rolling boil”, in Merriam-Webster Online Dictionary, Springfield, Mass.: Merriam-Webster, 1996–present.