Because, you see, that's what the Dayspire is: the Forge of the Heavens.
The Dayspire Revisited
Most folks on Pellatarrum look at the infinitely tall monolith which dominates their sky and assume it is mostly solid, albeit honeycombed with miles of Dwarven tunnels and halls. And while this latter assumption is indeed true, the former is most assuredly not.
The Dayspire is actually a pipe, and the Dwarves only live in the walls surrounding it. As the seasons tick past, the tip of the infinitely tall Dayspire actually touches the elemental plane above it, and in so doing, the contents of that plane pour down the hollow interior and into Pellatarrum itself, replenishing and renewing it.
Wait a second, I hear you asking. If the Dayspire is infinitely tall, how does it manage to hit the Elemental Planes? Isn't having two definite endpoints pretty much the definition of a finite distance?
Yes, this is an excellent question, which I shall answer thusly:
1. Fuck Euclid.
2. There's infinite and then there's infinite. If you were to start climbing the Dayspire using the handy Dwarven roads which spiral up its perimeter, you would never reach the top. Even if you were immortal, and had a crew of equally immortal Dwarven miners digging fresh tunnels ahead of you, in a million years you would never reach the top. This is because you are composed of matter, and the Rules of Creation -- which the Dwarves hard-coded into reality at the moment of Pellatarrum's concept -- state that matter can never, ever, bridge the divide between the Material Plane and anything else.
(Which is why you need spells like Gate and Plane Shift to cross the planes. Those don't bridge the gap, they create a shortcut between the two. Compare this to our current knowledge of "cannot travel faster than light" vs "using wormholes to get around this restriction".)
Energy, on the other hand, can and does travel freely through the Ether to Pellatarrum. If it didn't, then the Positive Energy Plane couldn't warm the land like a sun, and the Negative Energy Plane couldn't create darkness for sleeping. Ipso facto, energy can cross the infinite in a finite period of time.
But in that case, how can the Dayspire reach the planes? It's clearly made of matter and not energy.
It's also a giant magical battery, as at any one time a quarter of it is bathed in Positive Energy and its opposite quarter bathed in Negative Energy. And this energy cycles around it constantly, in a pattern of "Positive - Cooldown - Negative - Cooldown." In other words, it's an artifact of literally unfathomable proportion, and it's allowed to break the rules.
The Forge of the Heavens
To understand the seasons, all you must do is think of how a smith would work a forge:
- The forge is stocked with raw material -- the fuel for the fire and the items to be worked.
- A fire is lit and then carefully stoked to the proper temperature.
- Once it is hot enough, the materials are worked into their proper shape.
- The smith quenches the finished item to cool it, then puts the fire out to clean the forge for its next use.
This is the cycle of seasons within Pellatarrum:
- Winter (Elemental Plane of Earth)
- Spring (Elemental Plane of Air)
- Summer (Elemental Plane of Fire)
- Fall (Elemental Plane of Water)
So, to summarize:
- Raw materials (ore, minerals, etc) from the Plane of Earth flow down the Dayspire and are collected by the Dwarves. They cannot harvest it all, and the surplus flows down into the earth below them. (Note: the Dwarven colony within the Dayspire extends deep below the surface of Pelltarrum. They are very good at harvesting materials, and still they are unable to gather more than a fraction of this bounty.)
- Air flows into the Dayspire, clearing away much of the dust and dirt from Winter. This also helps to re-oxygenate the Dwarven tunnels. Spring cleaning occurs during this time, and anything unwanted is pitched down the pipe. Exhaust tunnels are opened in preparation for Summer, and collection hoppers are cleaned and put away. Forges are made ready and spells are cast upon them.
- Fire! Unfathomably hot elemental flame roars down the tube and is vented into forges. Through careful placement of forges and vents, Dwarven smiths are able to fine-tune the heat which flows through them, and they are able to forge anything during the summer months. Anything. Despite the use of spells and exhaust vents, and the placement of homes and common areas on the outer rim of the Dayspire, everyone ends up sweaty and sooty. This is not necessarily a bad thing among Dwarves, but other races find it almost uninhabitable.
- Torrents of water, both salt and fresh, gush through the great pipe and clear away the soot for the summer. Everyone bathes, washes clothes, and collects water. Great cisterns are opened to harvest this bounty (the water is later desalinated and purified if it is intended for potability.) The forges are put to bed for the year in a ceremony of quiet reverence. Soon enough, however, winter will come again and there will be more ore and minerals falling from the heavens, and to Dwarves, that is cause for celebration and rejoicing...
Each season as it affects the rest of Pellatarrum will receive its own detailed writeup during the week.