Heating water to boiling brings it to the same pressure as the atmosphere; it then changes from liquid to vapor, which bubbles up and breaks the surface.
Boiling it harder or longer makes it no hotter; only atmospheric pres sure alters the boiling point. At sea level, water boils at 212oF At higher altitudes, where the atmospheric pressure is lower, water boils at a lower point and also evaporates faster.
Elevation Boiling Point
A lower boiling point may require adjustments in time, temperature, or amounts of ingredients when cooking foods in water and when canning foods at high altitudes.