Here’s a starting point for those calcs: http://www.mide.com/pages/air-pressure-at-altitude-calculator

I’m thinking about half that, plugging in an altitude of -8000 into the second calculator.

Calculate Air Pressure at Altitude

Pressure at Sea Level  32000
Temperature 15 C
Altitude -8000

Air Pressure at Altitude = 76532

You’ll have to play around with temps and this is based on a 1G planet but they have a mars calculator as well; but Canyon wasn’t as cold as mars, IIRC.

> On Oct 16, 2016, at 5:00 PM, Christopher Sean Hilton <xxxxxx@vindaloo.com> wrote:
>
> Valles Marineris on Mars is 8km deep. How high would the mean surface
> pressure of Mars have to be to have a surface pressure of 75kPa at the
> base of Valles Marineris?
>
> I'm wondering about the viability of planets like Larry Niven's
> Canyon.
>
>
> --
> Chris
>
>      __o          "All I was trying to do was get home from work."
>    _`\<,_           -Rosa Parks
> ___(*)/_(*)____.___o____..___..o...________ooO..._____________________
> Christopher Sean Hilton                    [chris/at/vindaloo/dot/com]
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--
Bruce Johnson
University of Arizona
College of Pharmacy
Information Technology Group

Institutions do not have opinions, merely customs