Freezing at High Altitude

AT HIGH ALTITUDE DOES WATER FREEZE AT A HIGHER OR LOWER TEMPERATURE THAN AT SEA LEVEL? my guess is that it freezes at a higher temperature at high altitude than at sea level due to the lower pressure on the water.
- ROY KENDALL (age 63)
VISALIA

You're exactly right. Since the liquid has less volume than the ice, lower pressure favors the ice. That raises the freezing point.

Mike W.

(published on 05/07/2011)

This answer seems to be wrong. The freezing point of water doesn't go above 0C as pressure decreases (well OK, to 0.01C at 1/100th of an atmosphere). Check out water's phase diagram on this page: https://en.wikipedia.org/wiki/Phase_diagram
- SG (age 25)
Amherst, MA, USA

You're right that it is a very small effect. Our answer was only meant to tell the reader that his reasoning about the effect was qualitatively right, not that it had a big practical significance.

Inga K. points out that for water boiling, with about 10,000 times as large a volume change as for water freezing, the effect of altitude is very noticable.

Mike W.

(published on 04/21/2020)