World Sundering

Since Medieval Stasis makes it so that a Magical Land will always be the same, and that 1,000 or so years in their world has the same amount of political, economic, and technological development as about five years in our world - that means that natural change happens pretty much never. Including geological shift. The continents, landmarks, etc. will remain in the exact same way they are across a span of 10,000 years, so the prophecy about the Sealed Evil in a Can in the Mountains of Shadowblood Peak will always be fulfilled without having Shadowblood Peak turn into the Shadowblood Picnic Hills thanks to erosion.

With one exception: World Sundering. Used as part of Expansion Pack World, to revamp a setting, the World Sundering is a huge magical explosion that does the job of millions of years of geological shift in a few seconds. Generally, an evil wizard, an Artifact of Doom, or some other event causes all of the continents of the world to shift rapidly.

This allows writers to set two stories ten years apart in a world that's completely different from the old one.

Geological change in these worlds doesn't happen because of tectonic plates or any nonsense like that. A Wizard Did It. Always.

Overlaps with The End of the World as We Know It. See Also: Patchwork Map, Earthshattering Kaboom, Colony Drop, Atlantis. Contrast World-Wrecking Wave.

Examples of World Sundering include:

Anime

The world of Slayers was shaped due to the battle between the god Flare Dragon Ceifeed and the demon lord Ruby Eye Shabranigdu. Their battleground by Lina's time 4000 years later is in the center of a huge almost circular ocean.
Digimon Xros Wars has the Digital World split into numerous Zones, the implication being that they were once one. They are merged into seven Lands halfway through.
- The original Digimon Adventure has a minor/delayed example, with the Big Bads warping a giant mountain into existence and turning themselves into Load Bearing Bosses for different parts of the world (killing the water-themed villain removes the oceans, etc.). In addition, the entire Digital World is essentially rebooted in the time between the final battle and Digimon Adventure 02.

Literature

Older Than Feudalism: Atlantis, according to Plato, was caused to sink beneath the ocean in a single day by the gods.
The Trope Codifier is JRR Tolkien, of course. This happens at least three times in The Silmarillion: the original battle between Morgoth and the Valar leads to the creation of an ocean with Valinor on the Western side of Arda and the great inland Sea of Helcar in Middle-Earth; the War of Wrath at the end of the First Age causes the entire subcontinent of Beleriand to sink into the ocean; and the Drowning of Númenor is accompanied by a divine intervention which makes the entire world round rather than flat. Finally, it's implied that Middle-earth is simply the Old World in a lost era of prehistory, so untold other cataclysmic changes would have occured between the setting of the novels and the present day to account for modern geography.
David Eddings' Belgariad series has this in the backstory, related in the prequel Belgarath the Sorcerer. When Belgarion acquires the Orb of Aldur (which caused the sundering at Torak's command), he muses about the destruction... and the Orb starts giving him precise instructions on how to fix it (he declines, for numerous reasons).
The Breaking of the World in The Wheel of Time. Half the wizards of the world did it as the Big Bad caused all men with magical power to go violently insane. In a highly advanced Magitek culture that had spent the last few decades in a desperate arms race.
Margaret Weis & Tracy Hickman have a world-shattering cataclysm, actually called "The Sundering," in The Death Gate Cycle. This time it was a Knight Templar that did it.
The (implied nuclear) apocalypse from thousands of years ago in the Shannara series. The apocalypse changed the geography of the world, meaning that magical locations, etc. from before could not be located later. Then again, Shannara mostly averts Medieval Stasis anyway.
- Less implied and more explicit in the recent series bridging the Shannara and the Word & Void series'.
Happens in some of the early Witch World novels by Andre Norton. The Witches of Estcarp use all their power (and in some cases, their lives and sanity) to twist and turn the mountain range between their country and the neighboring, invading kingdom of Karsten. This event is unimaginatively dubbed The Turning. This effectively kills the invading army and makes the mountains nearly impassable for any future invasions. Later, it's revealed the same thing was done thousands of years ago when the Old Race fled out of Escore to Estcarp.
Hyborian Age Europe in Robert E. Howard's Conan stories underwent such shifts to become the Europe we know today. In Conan's day, the Mediterranean is solid land, its future southern border delineated by an extension of the Nile; the Black Sea is considerably larger, stretching northward to form a continental divide; and the English Channel and much of the northern Atlantic are above water, linking Britain, Iceland, Greenland, and Newfoundland to the European landmass.
- It also suffered one before, when Atlantis sank.
- Interestingly, the above tallies quite well with what Europe apparently looked like a few tens of thousand years ago.
Michael Reaves actually broke a planet, then wrote a novel about the thousand-years-later aftermath in The Shattered World.
Averted in Glen Cook's Deadly Quicksilver Lies, where natural geological change really does take place in a fantasy setting and caused a buried treasure -- one everyone in the book is fighting each other over clues to -- to collapse into the sea, courtesy of plain ol' cliffside erosion, several hundred years ago.
Inverted in Brandon Sanderson's Elantris. The Chasm was probably created by a natural earthquake, but the changed landscape actually causes a breakdown in magic. Elantrian magic is based upon runes (Aons) that mimic the shape of the kingdom, so when the kingdom changes, the Aons stop working.
Done rather bizarrely in the second quadrilogy of The Runelords: in the second book of it (sixth overall), the main character fuses his world with another. 95% of the world from the first quadrilogy vanishes, unresolved.
The Heralds of Valdemar series has this as part of the Backstory—the entire modern world of Velgarth was shaped by the Cataclysm, a gargantuan magical explosion caused by the combined deaths of the two most powerful mages the world had ever known, along with all their magical artifacts. The Cataclysm turned a swath of fertile farmland into a crater hundreds of miles in diameter, another into an inland sea, and formed a hellish borderland of magically warped creatures that persists three thousand years later.
Paul Bunyan was this trope solidified into human form, being responsible for just about every major geographical feature in America. Minnesota's ten thousand lakes? Paul's footprints that filled up with water. The Grand Canyon? What happened when Paul dragged his axe behind him. The Mississippi River? Dug by Paul so he could float his logs down the country. The Rocky Mountains? Well, all that dirt he dug up making the Mississippi had to go somewhere. Michigan happened when he lost his left mitten.
In The Saga Of The Exiles, an actual geographical event in the shaping of Europe as we know it is the (very) direct result of character actions. We're talking "Grab the faultline with telekinesis and pull" levels of directness.

Tabletop Games

In Forgotten Realms the spellplague, among other things, radically changed the geography, from widening seas with the collapse of underground tunnels to the replacement of an entire continent with one from the lost world of Abeir.
The Cataclysm in Dragonlance.
- Also the Dragon Overlords in the Fifth Age.
Mystara suffered through several such cataclysms, most recently the Wrath of the Immortals.
The Grand Conjuction shook up Ravenloft a bit, although the small size of the Core means it was a more modest calamity than most of those listed here.
Exalted, as usual, takes this trope up to eleven; before the Primordial known as "She Who Lives Within Her Name" was banished to Malfeas, she detonated three globes of her unquenchable flame on top of Creation, literally Retgonning nine-tenths of everything that had ever existed up to that point in time. Even people who lived through it can't remember the things she deleted, knowing only that most of Creation is gone.
Magic: The Gathering examples:
- There was a pair of mini-blocks in a setting like this; it started out as the idyllic, Lighter and Softer Lorwyn, but then the Great Aurora occurred and changed the plane (and set) into the much less friendly Crapsack World Shadowmoor.
- The Overlay, Yawgmoth's plan to invade Dominaria, is one extreme version of this trope. During the Invasion block, several things happened to change Dominaria's face, so that when the war was over, Skyshroud Forest (part of the invading plane) was part of Dominaria, and Teferi's magic had shunted Zhalfir and part of Shiv into another dimension. When he tried to bring them back during the Time Spiral block, the rifts caused by his original shunting hindered the process: He was able to return Shiv, but Zhalfir was lost to the rift.
- Alara was one plane that became five, each missing two allied colors of magic and having a concentration of their more common enemy, when an incredibly powerful planeswalker ripped the world into pieces to strip away its mana. (So, for instance, Esper, lacking the individuality of red and green, is a world of machines.) In the Alara block, they smashed back together like cosmic bumper cars, accompanied by much asploding.
Occurred in the backstory of the Warhammer Fantasy Battle world, when the dimensional gates built by the Old Ones collapsed, resulting in a huge blast of magic energy, followed by massive earthquakes and an enormous demonic invasion. The most notable result in the present day is the existence of the Chaos Wastes on both poles.
- A smaller-scale one occurred when the Elves were forced to sink part of their homeland beneath the waves to contain the magic energies released from the aforementioned cataclysm in order to keep the entire world from being torn apart, and later when the Lizardmen decided to use their magic to alter some mountain ranges, leading to the destruction of several Dwarf holds.

Video Games

Lineage 2 evoked this in its latest Expansion Pack World Awakening with the release of the death goddess Shillen from her prison, which resulted in the destruction of many many many zones, namely Elven, Dark Elven and Dwarven starting villages and the Seven Signs completely wiped out of existence.
The Warcraft franchise has this in its backstory, and is one of the Trope Namers.
- The Frozen Throne has Ilidan attempting this with Northrend and failing due to Maiev and Furion. Even though he was trying to off the Lich King, it would've caused a global catastrophe had he succeeded.
- World of Warcraft does it again in Cataclysm. A Dragon did it!
  - It wasn't as severe as the first sundering, as most of the effects of this sundering were very minor in comparison (aside from opening portals to different parts of the Elemental Plane everywhere), but it counts. The larger plan was to make it much worse.
- Thousands of years prior to the events of Warcraft, the War of the Ancients lead to an event called The Sundering, where the Well of Eternity imploded, blowing up half the world's landmass, and splitting the one continent into three.
- Also, the planet Draenor, where Orcs are originally from, was torn apart by the use of too many portals, turning a once beautiful world into a Floating Continent in space.
As does EverQuest II.
This is being planned for Guild Wars II.
- It already happened once in the backstory to Guild Wars, with the City of the Gods being destroyed in a last-ditch attempt to stop the Charr invasion. The entire nation ends up a broken string of uninhabited islands.
Dungeon Siege II: Broken World
Hyrule being magically flooded in The Legend of Zelda the Wind Waker.
Used in the meta-plot of .hack's second series of games. In The World 2's backstory, a war between the humans, elves, and gods happened that destroyed the old towns and landmarks to make new ones.
Oracle of Tao, in the first scene! The world is split into Earth and the Void.
Tales of Phantasia, Tales of Symphonia, and Tales of Symphonia: Dawn of a New World take place in the same setting with a (literal) world sundering and world re-merging between each game. It was originally one planet, then split in two, then put back together again.
- 'Video Game/'Tales of the Abyss has a very weird variation. While the Big Bad is the one who gets the ball rolling, it's your party that finishes the job.
- Tales of Legendia has this as part of its backstory, twice. To wit: the world was once entirely ocean. Then the Orerines came along and used the Wings of Light to create an entire continent. At some later point, the Ferines got ahold of the Wings of Light and used it to destroy half of that continent. This is a bit of an odd example in that none of the gameplay even takes place on the continent in question.
Similarly, Final Fantasy V has a single planet which is magically separated into two worlds in the backstory, and then fused back together by Exdeath mid-game.
The cataclysmic destruction brought about by Kefka in Final Fantasy VI.
In Chrono Trigger, there were two world-altering cataclysms: the Fall of Zeal, in which an awakened Lavos annihilated the Magic Kingdom and flooded 90% of the world; and the Day of Lavos in 1999 AD, which razed the entire planet. Lavos' arrival in 65,000,000 BC didn't change the face of the planet per se (it only created an impact crater and killed off the dinosaurs) but the subsequent Ice Age and millions of years of tectonic shift did.
Frequently happened on Graal Classic pretty much whenever the admins got bored - a cataclysm and an island appears, a cataclysm and it merges with the continent, a cataclysm and it gets invaded and burned down, a volcano erupts and another island sinks...
Golden Sun had a ~~minor~~ version of this in the events between the first game and the second, caused by the activation of Venus Lighthouse. At first, it seems that its greatest effect was to break an island off of one continent and drift it across the ocean (with some important characters brought along for the ride). During the opening of the second game, though, it's revealed that it also caused a massive tsunami that (as you find out later in the game) awoke an ancient monster from slumber and moved one continent for miles until it slammed into another.
- Another case seems to have occurred since the release of Alchemy at the end of the second game, judging by the map for Dark Dawn. Particularly noticeable are the apparent sinking of Tolbi, the expanded mountain range near where Altin should be, the fact that Kolima Forest is on a completely different part of the continent it's on (and also more confusing), and the waterfalls between different levels of ocean.
This arguably describes the most devastating event in the Mega Man series: the Elf Wars, a time period between Mega Man X and Zero. The world is completely devastated, with ~~possibly~~ only one bastion of civilization left. Also, there's a radical decrease in the population (60% humans, 90% Reploids wiped out). It's all the cause of Energy Beings with the power of Mind Control and Rewriting Reality, which are in the hands of a Omnicidal Maniac Complete Monster. The war, which spanned only 4 years, was thankfully ended by the duo of the series' heroes before things got much, much worse.
A staple of the Ultima series, and even key to multiple servers in Ultima Online.
In Xenogears (at least in the Perfect Works), the global thermonuclear war that wipes out nearly all of humanity 6000 years prior, actually causes cataclysmic movement of the planet's tectonic plates.
Happens to the titular age of Riven at the end of the game.
In The Tone Rebellion, the intro shows an enormous continent in space populated by peaceful Floaters. Then The Corruption appears and spreads throughout the land. The war with it results in the continent being split into dozens of smaller islands, all orbiting a central one - the heart of the corruption. Four of these islands have the remains of the Floater race. Over the next millennia, the four tribes evolve into distinct subspecies, each in alignment with one of the four elements (Natural, Supernatural, Physical, and Ethereal). After activating all the ancient bridges between the islands and defeating the corruption, the player witnesses the islands drifting towards each other and re-merging into the original continent.
Averted/subverted/played straight in STALKER where after the second Chernobyl disaster radiation, psy waves, mutants, gravitational anomalies, and more spill out into the Zone. Enormous radiation emissions happen daily which kills anything that hasn't taken cover. But despite all the catastrophic results, the geography of the area remains more or less the same. However in the sequel, Call of Pripyat, you see that the anomalies have started to warp the terrain. Gravity anomalies are creating bizarre rock formations, burner anomalies are causing areas that were formerly stone or concrete to melt, acidic anomalies are causing strange plant growths all over, and generally the anomalies are twisting around the landscape.

Web Comics

Parodied in Penny Arcade's The Elemenstor Saga, in which there are several of these. Usually one every few thousand years. One was caused by a giant cow falling from outer space.
Happened four times in the backstory of "The Dragon Doctors". One was a magical civil war, one was a nuclear war, one was a meteor impact, and the most recent was the most devastating; "The Dimension Fusion," combining bits and pieces of other worlds into this one.