erupt

The Latin picture is literal: eruptus comes from e "out" and rumpō "to break", so something breaks out of the ground. In grammar, the volcano or geyser is the subject, and the verb takes no object. What comes out follows in a separate phrase, as in the volcano erupted, spewing lava. Lava, ash and water are what pour out, but the mountain is what erupts.

Teeth erupt too. In this use the word means a tooth breaking through into view, and a third molar may erupt late or never appear at all. That quiet, literal emerging sits beside the sudden applause and protests of everyday use. Unlike the volcanic meaning, nothing is thrown out. Something simply appears where it was not before.

Here feelings break out instead of rock. The emotion usually follows in or with: a crowd erupts in anger, and a stadium erupts with joy. The subject is often a crowd, or even a place standing for the people in it, like Stamford Bridge. The image can also stretch past emotion. Physicists write of infinities that erupt when calculations are pushed into new domains.

A naturalist's term for a population on the move rather than merely growing. After an unusually good breeding season, flocks spill out from their breeding grounds and turn up in places, such as reed beds, where they have not been seen for years. The verb is intransitive and pairs with from and with direction words: birds erupt from a range, or erupt southward. It keeps the Latin image of breaking out behind the general 'burst forth' sense.