# ice melting point, Mt Everest

**URL:** <https://boards.straightdope.com/t/ice-melting-point-mt-everest/147427>\
**Category:** Factual Questions\
**Created:** [January 9, 2003, 2:36am UTC](https://boards.straightdope.com/t/ice-melting-point-mt-everest/147427 "2003-01-09T02:36:09Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Scorpio](https://avatars.discourse-cdn.com/v4/letter/s/a88e57/32.png) [@Scorpio](https://boards.straightdope.com/u/Scorpio)\
**Post date:** [January 9, 2003, 2:36am UTC](https://boards.straightdope.com/t/ice-melting-point-mt-everest/147427/1 "2003-01-09T02:36:09Z")

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This should be easy but I can’t find it on the net:

Boiling point is lower at the top of Mt Everest, so water boils at 75 degrees C instead of 100. Melting point is higher, so at what temperature would ice melt at an air pressure equivalent to that at Mt Everest (9000m approx above sea level)?

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**Author:** ![raygirvan](https://avatars.discourse-cdn.com/v4/letter/r/ac91a4/32.png) [@raygirvan](https://boards.straightdope.com/u/raygirvan)\
**Post date:** [January 9, 2003, 3:12am UTC](https://boards.straightdope.com/t/ice-melting-point-mt-everest/147427/2 "2003-01-09T03:12:37Z")

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No precise answer, but near-as-dammit zero Celsius. You can see from the [water phase diagram here](http://www.sv.vt.edu/classes/MSE2094_NoteBook/96ClassProj/pics/941.jpg) that melting temperature isn’t much affected by pressure within the range we’re talking about.

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**Author:** ![Scorpio](https://avatars.discourse-cdn.com/v4/letter/s/a88e57/32.png) [@Scorpio](https://boards.straightdope.com/u/Scorpio)\
**Post date:** [January 9, 2003, 3:15am UTC](https://boards.straightdope.com/t/ice-melting-point-mt-everest/147427/3 "2003-01-09T03:15:08Z")

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Ah, I see, thanks very much.

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**Author:** ![raygirvan](https://avatars.discourse-cdn.com/v4/letter/r/ac91a4/32.png) [@raygirvan](https://boards.straightdope.com/u/raygirvan)\
**Post date:** [January 9, 2003, 3:43am UTC](https://boards.straightdope.com/t/ice-melting-point-mt-everest/147427/4 "2003-01-09T03:43:35Z")

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For a more precise answer, check out the “melting curve” for water. The figure for the slope, which you may want to verify, is -134 atmospheres per Kelvin! That is, raising the pressure 134 atmospheres drops the melting point by 1K (i.e. degree Celsius). Or conversely, dropping the pressure by 0.1 atmospheres raises the melting point by 0.1/134 degrees = 0.00075 degrees. It’s late and I can’t be bothered to work out the pressure in atmospheres at 9000m, but you should be OK from here on.