Geologically speaking, a stack is a steep column of rock just off shore in a coastal area. Other names for the same general formation are sea stack, kekur or rauk.
Stack formations tend to start as a cliff, headland or peninsula, but slowly water and erosion eats away at one or small cracks or weak spots in the rock. The cracks form a cave, which then opens on both ends and grows into an arch. Eventually the arch collapses, leaving just a narrow island-like stack isolated out in the water. Eventually, erosion will cause the stack to collapse into a stump, an island of rock that vanishes beneath the waves at high tide, and eventually even the stump will likely wear away.
Such formations tend to become home to colonies of nesting sea birds. Their remoteness keeps the birds and their young safe from most predators.
Stacks that survive more than a decade or two tend to take on names, myths, and possibly even personalities. Such jutting columns of rock are often personified, and called things like "The Old Man" or "The Three Sisters".
Game and Story Use
- Stacks are an interesting way to illustrate the slow erosive forces of time in a time-travel game, or a game where the PCs are immortal. You can drive home the themes by illustrating how the same place is transformed over the ages. From peninsula to archway to stack to stump or island. It's a chance for the GM to get artsy, or let the Time Abyss wax philosophical.
- A crunchier tactical game system can make this functional as well as artsy. If you prepare different battlemaps for the area in each time frame, you can create a strong sense of place that reinforces the themes and presents increasingly greater tactical challenges.
- An ancient altar, temple, or other holy ground was once high on the headlands overlooking the sea where the old gods slumber. Now, it's stranded out upon a stack, all but inaccessible. Unfortunately it's the only place where the ritual can be conducted that will:
- save the kingdom.
- plunge the world into darkness.
- An old abandoned castle, tower, guard post, beacon, wizard's tower, etc was likewise once upon a peninsula that is now a stack. In this scenario, though, a band of goblins, ratmen, mermen, or the fair folk have moved in where man no longer treads. The PCs mean to drive them out and loot the place.
- In a modern setting the PCs - or the enemy - can set up an OP, radar or signal station on a stack overlooking a crucial strait or bay. They may even be able to get heavy weapons or ordnance up there to make a real nuisance of themselves in a reacreation of the HMS Diamond Rock business.
- An old stack that's been there for ages collapses.
- Perhaps it leaves treasure, artifacts or fossils amongst its ruins. Something valuable the PC (and others) might seek to possess. An expedition to retrieve it must be mounted at once, or it will be lost beneath the waves.
- A rare species of insect, mollusk, or bird lived only on that stack, having been separated from the mainland for over a hundred years. When the stack collapsed toward land, a few of them made it ashore, and are now a nuisance to local agriculture, or perhaps even a danger to the people themselves.
- It was a named and personified stack, such as "The Old Man of Misery Bay", and numerous local traditions abound about strange happenings near the place. Since the collapse, those strange and mysterious happenings have spread inland. The locals are certain it's the Old Man himself, no longer bound in the fallen stack and thus free to bring his misery and schemes far and wide. Is this truth, or just foolery? The PCs are hired as expert investigators on the supernatural, and tasked with getting to the bottom of it all.
- In a fantasy setting, a stack could form for mystical reasons. You could throw geology out the window, and declare all stacks are actually magical sites. Or, you could simply increase the frequency of stacks, because they form due to magic in addition to the normal scientific way.
- For example, if a protective spell were cast on a location, it might persevere and survive not just erosion, but any number of natural disasters.
- Stacks, being a point of conflict and defiance between two elements (earth standing against the encroachment of the water) could provide benefits for elementalism or other magic. Perhaps earth-attuned magic is extra potent when cast while standing on a stack, but is also has a slim chance of offending the God of the Sea in the process.
- In a suitably animistic setting spirits of the land - genii locorum if you will - could inhabit and protect parts of promentaries that would otherwise wash away, thus creating stacks. Personalisation of such a stack may even empower and re-inforce the spirit as though it were some kind of low end worship or veneration.
- Of course, if the stack ever does collapse it could release an angry, displaced spirit as noted above.
- A stack with the right qualities might be home to mythical birds or flying beasts, like the Roc, the phoenix, or the Ziz.