World-Building Geography Help: Polar Seas

[VirgilCaine]

Here's my best answer to all your questions, and you're probably going to hate it:

Yes, if that's what you want.

Seriously, you're creating the world. It can work however you want it to work. Real-world geology and tectonics don't matter, unless the party is comprised of geologists and adventures are going to focus on taking core samples.

The PCs aren't looking down on your world like a map. They're in the thick of things, wondering where the next tavern is. IMO, fleshing out that tavern is way more important than making a geologically-realistic map.

I will now get off my soapbox. Apologies for the diversion.

I agree.
Just focus on making the world "do what you want" and not so much on how it would get that way--this is a world where theres several deities--more in published settings--to mess around with nature.

 

[Sado]

An idea that I considered. As you want a ring of mountains right at the appropriate latitudes. You might want to consider a gigantic impact crater at each pole. I know, the statistical chance for this to happen exactly at both poles would be unreal.

You could say the planet's past civilizations earned the wrath of the gods who sent two planet killer meteors, one at each pole simultaneously. The impacts would create the exact geologic features you want, and potentially caused the enirvonmental change that made a desert of the whole planet. Thousands of years later, whatever water wasn't thrown into space by the impacts would have settled in the gigantic craters at the poles. Civilization of the remarkable survivors would then rebuild anew.

How large of an object would it take to make such an impact crater covering the highest 25-30 degrees latitude?

I agree having one such object hit each pole is a bit far-fetched, but I'm rather fond of the idea of two thriving areas of civilization clustered around the polar seas with a vast impassable desert (with its own strange life forms) separating them.

 

[argo]

Many good points here but I'll throw in my two cents anyway. All this is off the top of my head but I hope you'll find it usefull. An issue nobody has addressed yet is the atmospheric action. Taking our earth as an example we have the phenenom of equatorial lows, Hadley cells, Subtropical highs, jet streams and polar fronts. The equatorial region on earth recieves high ammounts of Insolation (sunlight) which for our puropses is simply energy. Imagine that we follow a single air "packet" on its trip through the atmosphere. The high energy reciepts cause moist air at the equator to rise (equatorial low pressure zone) and as it does so expand and dump its water; thus you have wet rainforests at the equator and tropical regions. The air rises until it reaches an inversion layer in the atmosphere and then spreads out north and south. Eventually the air will cool enough to begin contracting again and sink towards the earth, as it does so its pressure and temperature increase until at sea level you have a hot blast furnace of dense, dry air crashing down: the Subtropical High pressure zone. This is one reason why on earth you find deserts in the subtropical latitudes. The air at ground level again spreads out to north and south, following the path south the air picks up moisture as it moves southward towards the equator and starts over: this aciton completes the Hadley Cell; a pocket of tropical air bound between the equatorial low and subtropical high.

Looking at the high latitudes things look a little different. The air over the poles is extremly cold compared to air in the mid-latitudes. This translates to it being very dense and thus hugging the ground tightly, effectievly forming a dome of dense air over the poles: the Polar Front. Where the polar front meets the mid-latitudes the compariatevly warm (less dense) and moist mid-latitude air is driven up the wall of the polar front much the same way it might go over a mountain range and with much the same effects: heavy precipitation all along the front. Consequently little mid-latitude air breaches the polar "dome" and this accounts for the small ammount of precipitation we get at our poles; as was mentioned above many polar regions get little precipitation but have also loose little to evaporation thus they accimulate ice packs. Mid-latitude air that rises over the polar front becomes the polar jet stream.



So how might this apply to your world? Well you defenaetly do want to start by making the polar regions a lower elevation than the equator in order to get your oceans. Secondly, in order to have liquid oceans at the poles you will want the planet to recieve more insolation (closer to the sun, hotter temperatures) than our earth, this is fine as it will help establishing deserts in the lower latitudes but I don't think you will be boiling water at the equator: any planet that hot probaby couldnt' support life at all. The Subtropical Highs would work perfectly for you: if you had a world with no tilt to the axis you would get subtropical highs with no seasonal variation thus curtailing seasonal storms (monsoons) that keep some subtropical regions on earth moist. If the effect of these high pressure zones were stong enough then you would have large deserts covering most of the sub-tropical and lower-mid-latitudes. You could have a thin band of equatorial rainforest or make the equatorial region a desert depending on how much water you allow to exist in the equatorial sytem at the start. Looking at the high-mid-latitudes and polar regins I think it would look a little different from our earth. The effect of the liquid polar oceans would preclude the existance of a polar front, I think. Since oceans create more of a moderating effect on the atmosphere I think that you would not have the "cap" effect that we assoicate with the poles on earth and thus you would not get the violent storms along the polar front. Instead you would have more of a costal effect that rings the entire mid-high-latitude. Lets look at this as just one possibility: since you have the ocean covering the poles and extending down into lower latitudes (and greater insolation) I imagine that your dominant ocean currents will be upwellings of cold water along the coasts, surface warming, upper level currents moving poleward, and finally cooling and downwelling at the poles to repeat the cycles. Cold upwellings along the coast would mimic the effects of cold polar ocean currents that we assoicate with western coasts on real world contients. Fruthermore if you want polar "capstone" plates subducting under mid-latitude plates in a ring of fire effect that would produce geography similar to the western North American continent.

So my advice to you is to look to the climate and ecosystems of the west-coast United States. It varies with latitude from the deserts of southern califorina to the costal rain forests of oregon and washington. Pick the ecosystem you like and set the coastline of your polar ocean at that same latitude as that ecosystem. For some ecosystem variation introduce latitude variation along the coastline in the form of penesulas or interior ocean extensions.

Hope that helps.

 

[Sado]

So my advice to you is to look to the climate and ecosystems of the west-coast United States. It varies with latitude from the deserts of southern califorina to the costal rain forests of oregon and washington. Pick the ecosystem you like and set the coastline of your polar ocean at that same latitude as that ecosystem. For some ecosystem variation introduce latitude variation along the coastline in the form of penesulas or interior ocean extensions.

Hope that helps.

Good point. I suppose the climate in the civilized areas round the ocenas would not vary too much, assuming the ocean was centered on the poles.

Another thing I just thought of. If the planet isn't tilted on its axis, not only would there be no seasons, but at the poles would there be a day-night cycle?

 

[Pbartender]

How large of an object would it take to make such an impact crater covering the highest 25-30 degrees latitude?

Very large. Consider that something large enough to make such a large crater would likely exterminate all life on the planet. The impact would have to happen early in the planet's life to avoid that.

I agree having one such object hit each pole is a bit far-fetched...

Two such large objects striking opposite each other would be an extraordinary coincidence.

However, take a look at Mimas, a moon of Saturn... At sometime in its past, it was struck by a very large object. The object left a crater large enough to make Mimas look an enormous eyeball. The crater is 130 km wide (almost 1/3 the diameter of the moon itself). It has walls that are about 5 km high, parts of its floor reach 10 km deep, and its central peak rises 6 km above the crater floor.

The force of the impact was so great, that it caused a series of fractires in the moon's crust to create rippling mountains and valleys on the exact opposite side of the moon from the impact.

 

[Sado]

I found this regarding the crater on Mimas:

If there were a crater of an equivalent scale on Earth it would be over 4000 km in diameter, wider than Canada.

Could a planet the size of earth survive an impact with a body large enough to cause this?

And what causes that big mountain in the middle of the crater? I would have thought it would be flat, or depressed.

 

[Pbartender]

Could a planet the size of earth survive an impact with a body large enough to cause this?

It is theorized that Earth's moon was created by just such an impact.

And what causes that big mountain in the middle of the crater? I would have thought it would be flat, or depressed.

Simply put, complex craters (those with peaks, ridges or extra rings in the middle) occur when the impact energy is enough to make the planetary surface temporarily act as a fluid.

In other words, the ground that the meteor is hitting 'splashes' like water and gets re-frozen in mid-splash. Go find a slow-motion movie of a water drop splashing into a pool of water, and you'll see what I mean... https://www3.imperial.ac.uk/pls/portallive/docs/1/11264.GIF

 

[Sado]

Back to that map of Mars a few posts up...

What kind of climate would a world like that have, assuming it was earthlike in all other respects (size, distance from sun, etc)? Would there still be an icecap at the poles? Would the equatorial coasts be tropical like they are on earth? Would most of the southern hemisphere be a big desert?

 

[Pbartender]

Back to that map of Mars a few posts up...

What kind of climate would a world like that have, assuming it was earthlike in all other respects (size, distance from sun, etc)? Would there still be an icecap at the poles? Would the equatorial coasts be tropical like they are on earth? Would most of the southern hemisphere be a big desert?

Assuming that all else was the same as earth, it would have roughly the same types of climate zones... Perhaps they would be rearranged a little differently due to geography, but there would likely still be ice caps, deserts, forests, plains, jungles, swamps, etc...

 

[Gez]

However, take a look at Mimas, a moon of Saturn...

It's not a moon... It's a space station!