Where does the bubble come from in the bubble model?

I understand the basic outline of the bubble model ( gases from hydrothermal vents in the ocean floor get trapped in bubbles, those bubbles reach surface, where they pop releasing those trapped molecules, those molecules fall, potentially getting trapped again, starting the whole process over ) but where do those bubbles trapping the gases come from ?Where does the bubble come from in the bubble model?
The bubbles are the gas. Think of the sun, it's a perfect sphere because that's how gravity works. Same thing but there's pressure from the water pushing inward. It just so happens that the gas collected together to form a pocket. It's also like water boiling.