Yere all not thinking straight on this.
The water won't all flash to steam at once as the pressure will keep it from
doing so. There is no overpressure possible as the higher pressure will
stop the water from turning into steam. It is a balance that is a basic
function of nature. Otherwise, you'd have boilers suddenly turning their
water into steam at huge pressures and the boiler blowing up! It jest don't
happen that way!
For a particular temp, the boiling point is set and the temp needs to go up
to get more pressure to occur. Without that temperature increase, the
pressure keeps putting the steam back into water as a natural balance that
never gets out of whack.

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Why isn't there an Ozone Hole at the NORTH Pole?