Geological / environmental event
The Great Schism occurred near the end of the Age of Dragons. The war between the scaled creatures had become so violent and catastrophic that Nunata, the land of dragons, was ripped apart to become the mysterious floating islands that it is known for today.
The Schism was the beginning of the end of the Great Dragon Wars. It resulted in many casualties on both sides, including the elves who were new to Eraba (The Material Plane). The force of several dragons hitting each other in a single attack was so great that it ripped apart the continent of Nunata. The residual magic from the attack was so strong that it caused the different pieces of the continent to float in the air, varying from barely out of the surface of the water to several hundred feet in the air. Even more than 10 000 years later, the residual magic is still strong enough to keep the islands floating. This could be in part to the fact that the local, scaly skins of Nunata are very hostile to outsiders preventing them from entering onto the floating islands and tapping into the raw magical energy surrounding the islands.