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.

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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^[1]:

     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.