A Very Deep Valley: How Weird a Climate Can I Get?

[tarchon]

If the OP will forgive a slight threadjack, what exactly is 'partial pressure'? I've been hearing it around for years, but nobody has been able to give me an explanation I could really assimilate.

The term comes from Dalton's Law of partial pressures. For a mixture of gasses, the total pressure is the sum of the pressures of the component gases, like P_air=P_N2+P_O2+P_CO2
If you combine this with the ideal gas law (PV=nRT), the partial pressure of a particular ideal gas is then just the (molar) percentage of that gas in the mixture times the total pressure. The reason this is usually significant is that most chemical reaction rates depend on the number of reactant molecules per volume, which is proportional to pressure (again, for an ideal gas). Since only the reactant gas is involved in the reaction, not all the other gasses, if you want to find the reaction rate of, for example, oxidation, you have to use the partial pressure of the reactant gas, oxygen, in the rate equation.

Another way to look at it is that the partial pressure of O₂ is the pressure the gas would have if you took away everything but the O₂.

 

[Nyeshet]

Hmm, another interesting idea: What if the valley was the result of a massive impact in an area littered with numerous massive caves in multiple layers? The impact causes their collapse, resulting in a deeper than normal crater, and if the region was on a high altitude plateau, then suddenly we have a valley deep enough for normal pressure - and temperate biomes - surrounded by steep cliffs leading to a region of frigid terrain with air almost too thin to breathe.

There could be real reasons for those within to think the cliffs are the walls of the world, and if the resultant crator valley is large and deep enough it could easily have its own weather systems. We could even go a little further. Perhaps an underground river once ran through the caves. Now it falls as a waterfall from one end and sinks into the ground in the other end.

As for partial pressure, it seems it is more of an issue than I thought. It seems that we can only descend as far as about 12-16k ft before we start having major fire issues (at least within the valley). Of course, this would also aid in dealing with massive insects (like the largest dragonfly on record: 2 ft wingspan! from the same period, if I recall correctly). And denser air probably would allow for larger flying creatures and even breathing less often (and possibly last longer while running due to the higher O2 intake, I presume).

Hmm. This suggests that perhaps all Fire based spells should be empowered &/or widened, and all endurance checks (whether for long distance running or holding one's breath) should receive a +2 to +4 bonus. Interesting ideas all round.