Defining 'the Great Cataclysm'

Michael O. Varhola
One of the defining events of the Swords of Kos Fantasy Campaign Setting is the Great Cataclysm, an event that took place a century before the action of the milieu and played a major role in creating it. In that we only look at the Great Cataclysm in hindsight in the Kos campaign setting, I thought it would be fair game to examine it as a prequel to the milieu for purposes of our DIY Apocalypse Challenge on “d-Infinity Live!”
∞ What is the name of your Apocalypse?
Everyone understands what is meant by “the Great Cataclysm,” and it is a relatively neutral label for the disastrous event of 100 years before, namely the eruption of the volcanic island of Thera in the center of the Aegean Sea. A number of other terms, however, are also used to refer to this event, and these generally reveal some sort of dogmatic bias. One of the most widespread of these is “Titanomachy,” a term for the war between the Olympian Gods and the Titans, which many religious people believe to be a spiritual event that caused or took place in conjunction with the eruption of Thera. Another term that has become increasing popular in the post-apocalyptic era is “Gigantomachy,” a term that has traditionally been used to refer to another great war, that between the Gods and the Giants.
∞ What forces are at work or play? 
On the most basic level, the Great Cataclysm was caused by the destructive eruption of the volcanic island of Thera, something that while terrible might have been a completely naturalistic event. As might be expected, however, in the post-apocalyptic era possible causes for the Great Cataclysm are a subject of ongoing inquiry and debate among many, from clear-eyed academics seeking the most probable explanations, to religious fanatics seeking to find or impose spiritual meaning upon the disaster. One of the most fevered explanations for the Great Cataclysm is proffered by adherents to the afore-mentioned term “Gigantomachy,” who subscribe to the belief that the Great Cataclysm was physically engineered by a powerful cabal of Giants, particularly volcano-dwelling Fire Giants, and specifically the Fire Giants who now rule the huge island of Trinacria (aka, Sicily).
∞ How does the world end? 
For the million or so people on or around Thera, the world ended when the core of the island was vaporized in the largest volcanic eruption in Human history before or since. For people in the thousands of cities, towns, and villages in a radius of about 100 miles, the world ended when a pyroclastic cloud of fire, burning ash, and molten sand swept across the seas in every direction, incinerating everything it touched and creating massive firestorms. For anyone still alive within a few miles of the shores of the Mediterranean or in low-lying areas along its coasts, it ended when gigantic tidal waves, raised up from the sea floor by the volcanic eruption, slammed into their communities, crushing and inundating them. For millions of people worldwide, it ended when ash from the eruption of Thera blotted out direct sun for several years, causing crops to fail and prompting widespread famine.
∞ Who and/or what, survives?
Within 100 miles of Thera, the only place where a significant number of people survived was the island of Kos, which was protected to a great extent by the pyroclastic cloud that came rolling across the sea by a headland that subsequently became known as the Aegis. Beyond the coastal areas of the Mediterranean, most people were not directly harmed by the Great Cataclysm and survived indefinitely in its wake (with many dying of famine, exposure, disease, and other conditions caused or exacerbated by the decade-long winter). Perhaps most significantly, however, many people and creatures that had retreated from the world of Humanity not just survived but were forced or prompted to venture out from their unseen realms. Subterranean folk like Dwarves and Goblinoids ventured up from caverns and underground halls devastated by earthquakes, Elves and Centaurs were forced out of forests ravaged by wildfires, and fell races like the ancient Titans reentered the world when the gates to Tartarus were broken open …