All of Cosmos (all the worlds of mortals and immortals), is balanced in the continuum of Chaos and Void, and the forces of entrophy gnaw at Cosmos at every turn, labouring blindly to return it to its primeval state. The workings of Chaos are most easy to perceive and understand, for they take the form of outright breaking of the laws of Cosmos, disruption of nature and tearing of the fabric of the world.
The fabric of the world was refined from primeval chaos, but the agency and method of this transformation is fiercely debated and fought over by almost all religions.
Occasionally, and usually as the result of magic use, quantities of Chaos slip through the fabric of reality into Cosmos, or pieces of Cosmos revert to its original chaotic plasm. Even worse, gates may open to create direct conduits between Chaos and Cosmos. All such areas are continually warping, growing or shrinking, but fortunately, Cosmos eventually repairs itself, like a living body throwing off a disease. To come into contact with zones of Chaos means death or worse.