Geological / environmental event
The area around what were the Golia Islands get sealed off, and then replaced with a haze of fog that later dissipates to reveal Breaksky Island
No matter the date of the first tears in the sky, the year’s conclusion would be as solid a calendar point as anyone could ask. At dawn on the 12th of Harvest Moon, the rifts above the Golia Islands joined as one, and expanded to a disk of stormy, swirling purple blackness some 750 miles in diameter in the middle of the Magarene Ocean. They remained in this state over the course of the morning. At noon, a magical wall of some kind extended down from the sky into the ocean. And around 2pm, before any scholar could investigate its properties (though many would later claim to have done so), the wall vanished and emitted a pulse of sound and force outwards that was, quite literally, heard around the entire world. When the few nearby sailors lucky enough to avoid being thrown into the sea by this outburst looked back towards the Golia Islands, they saw nothing but a thick fog rolling outwards across the sea. Within seven days, the fog had cleared enough for navigation. It was enough time for every enterprising monarch, demagogue, zealot, kingpin, and warchief to put canvas into the wind and mark a course for the Golia Islands. But by the 19th of Harvest Moon , the Golia Islands were no more. Instead, explorers found a new landmass at the back end of their spyglasses. This island would come to be known as Breaksky Island.