The hottest that plain water can get at atmospheric pressure is 212, the bubbles you see are because once water hits 212 the heat energy that is being put into the water is no longer raising the temperature, it is vaporizing the water at the bottom of the pan and makes the boiling water look like it's rolling. Pressure cookers work by increasing the temperature that water vaporizes thus increasing the temperature at which the water boils, so you can essentially boil things at hotter than 212.
WHO SAYS kids don't like science anymore! Thanks for that info. I was not paying attention in school.