A Shardpool is a non-canon term used to describe the liquid Investiture of a Shard, or a perpendicularity. This liquid is often collected in a pool of oddly colored water. These pools can appear on any world on which a Shard has stayed for an extended length of time. It's possible for an individual with the ability to use a Shardpool to Worldhop.
Several Shardpools have been revealed within the Cosmere books. Scadriel had one for Preservation and one which is less a "pool" for Ruin. Sel had one for Devotion (the dead Elantrians went there) and probably an unseen one for Dominion. The Tears of Edgli of Nalthis are probably fed by the Shardpool for Endowment. Sixth of the Dusk sees a similar phenomenon, but it's not linked to a Shard.
The Shardpools for Ruin and Preservation are now gone, and there's a new Pool for Harmony, plus a new god metal for Harmony.
Rock saw a man appear out of a warm pool high up in the mountains and the Worldsinger's apprentice (i.e., Sigzil) got really anxious upon hearing it. (This was revealed at the bar when Kaladin finally went out with his fellow bridgemen for a drink and Rock told the story that's like folklore to his people.)
Q&A with Brandon
Q: If a Shard were to divest itself from a planet, would the perpendicularity there disappear?
A: Normally the shardpool would cease to exist, but there are circumstances that could prevent the shardpool from disappearing.
Letter From the Cosmere
I wish life never prompted me to violence. If a situation has degraded into an all-out brawl, then I believe that all attending parties have failed. Forget achieving a positive result, at that point survival is about the only victory possible. Diplomacy, economics, and policy crumble in the face of open warfare. Sure people will cling to these things, convinced they are protecting their way of life. Yet this is a deception, a lie that one can profit off of fighting. The only victory in war goes to those who win, and those who get on the good side of the winner. I detest the boot-licking that follows a powerful military leader. Besides, death is a hefty price no matter what is gained. There are far better ways to fight an enemy or shape one's fortunes. And often the poor or unnoticed are the ones who suffer the most from the wars of nations.
I have learned that the keys to victory fit into three distinct locks. First, knowledge is power. Secrets and whispers can be bought from the right ears. In a world of subtlty and misdirection, knowing your opponent's mind is the single greatest weapon in an arsenal. I always find my sources, and am not afraid of doing my own listening. Next, a weapon should never be apparent, but hidden in plain sight. I was trained in the art of the knife, a messy if effective tool. I prefer the quarterstaff or cane. Many will overlook a stick of hardened wood over a sword or knife, yet in my hands I find the hardwood to be more than adequate in a pinch. I believe people should be like that, effective, efficient, and unobtrusive. Subtlty is an art, and a deadly one at that.
Finally, always have a bolt hole. All plans can fail no matter how well crafted. From slum lords to emperors, the ones who last are the ones who always have a backup plan to their backup plan. A bolt hole or a getaway carriage. This is the greatest advantage to being a ... traveler, and might be the reason why we are so hard to kill. We all know there is a way out that practically no one can follow us through. Shardpools.
Obviously you are aware of what I speak about, but I feel a need to clarify my own thoughts. I still know so little beyond speculation. For instance, I know I can use these Shardpools safely with the proper care, but could never explain how I do this, nor would I dare take another with me. The Cognitive Realm is a very dangerous place, and I don't know how many can survive the process of traveling there.
Shardpools, as I like to call them, are more commonly known as perpendicularities. This is the Realmatic term most often used to describe the strange phenomena that occurs in these pools. It is apparent that Shardpools are not lakes of water, but raw Shardic Investiture in liquid form. These pools are present on worlds where a shard resides and are a collection point for their power. Why these pools appear is beyond recorded history, and why they reside where they are physically is yet another enigma.
Perpendicularities contain so much raw power that they tear a hole in the universal fabric that usually separates the three Realms. The Cognitive and Physical Realms bleed into one another, and I believe the Spiritual Realm has also been broken into. I haven't ever stepped into that Realm, so I can't be sure. But I am in no hurry. Without knowing what makes up the Spiritual Realm in great detail, I dare not risk it. Perhaps someday, but for now I have a lot more to learn before I attempt such a journey.
Shardpools are often caught up in the lore of a people or nation. Surprisingly, most cultures that I have discovered don't seem preoccupied with these strange wellsprings. I wonder if anyone ever notices travelers like me climbing in and out of them from time to time. I try my best to avoid all contact when I emerge. Naturally my lack of language will only hinder me.
On that note, I will forever be grateful for my father's tutelage and my quick wits. I know how to learn and can do so quickly. While I feel I'll never keep up with a fraction of the languages that I've encountered, I make it work where I can. That might be the most difficult aspect of my travels, perhaps only surpassed by the strange foods I have to try. Can you believe that there are people who eat the horns and shells of animals? I was flabbergasted when I first tried the food of the Unkalaki.
These pools seem, for the most part, to be locked into a location physically. We know that on Scadrial the Lord Ruler shaped the world, but upon reflection it seems that civilization was moved to the pools, rather than the pools themselves moved. However, this is only conjecture, and I highly doubt we could know for sure ourselves.
The only other fact I know for sure is that Shardpools are not on every world. In the Cognitive Realm you can see that there are other worlds out there. I've glanced through the fog of thoughts into their worlds, and yet there was no way to pass into their worlds physically. These Shardpools, as they are named, seem to be a consequence of a Shard's presence on a particular world. It makes me wonder how these other worlds became populated by humans. Is there some form of travel that has been lost to time? Are there ways to reach out and escape our worlds in the Physical Realm? More importantly I think is the question, if all these worlds have people who are so similar, did they all come from some original home? Why did they have to leave? Ah, but I tread into the obscure, more of my personal musing rather than theories based on observation. I just note how odd it is that while each world has diverse cultures and histories, we are still so similar. Perhaps there is something to these thoughts.
For now, I will continue to establish myself here. The current state of events on this continent is appalling. Normally integratiating myself is a lengthy process, but the current chaos in the nation of Jah Keved has made assimilation almost unnecessary. War is ripping this people apart and there are so many forgotten refugees. It's the most I can do to organize some few of these people into something productive. Their rulers are off fighting for succession, and those whom I find simply need a little guidance. I will not draw attention to myself, but I cannot leave them to be trampled and forgotten.
Despite all of that, there is a breathtaking beauty to this world. I wish I could put into words the sights and smells of Roshar. The crisp air and large open skies are the superlative aspect of this world. Everything here is rock, the massive high storms blasting away anything that is not protected. These violent storms are dangerous, and somehow majestic. They fling boulders and scatter life into hiding among the rocks. But when the storm passes there is a refreshing scene of clean renewal. I find myself stopping often to admire the alien beauty. And don't even get me started on the moons. The three crystalline orbs that arch through the sky at night are impossible to forget. I cannot help but watch them as they glide across a starry canvas. This journey, these years spent away from home, have been filled with wonder and beauty beyond anything I could have imagined. Perhaps the paths through the Shardpools have been filled with sorrow and failure, but I cannot regret the things I've seen. I may never wish to leave Roshar save for the knowledge that there are more wonders to explore, and new peoples to learn about. For now, there is a work to do upon these stones.
- Paraphrased from transcript.