The Elemental Planes & Shar

The Prime Material isn't the only plane that overlaps Shar. It's multiversal membrane warps and bucks in chaotic ways and sometimes aligns with areas of the Inner Planes, most commonly the Elemental Planes. When a cosmic collision like this occurs, it allows creatures and forces to enter Shar for a time, shaping it's landscapes. These events are called warps.

Forces from the Elemental Plane of Fire might cause the land to become hotter and more desolate while forces from the Plane of Water might drown the surrounding area, leaving bodies of water long after the Planes go their separate ways. Forces from the Plane of Air may cause severe windstorms, displacing and destroying anything in the region. Mountains could spring up seemingly overnight due to an overlap with the Plane of Earth. It is in these ways that the landscapes of Shar remain malleable and everchanging.

Warps vary in frequency, duration, and intensity. A warp may only last a day or two but have cataclysmic ramifications, such as the hypothesized events that paved the way for the Deadlands to become as they are. Conversely, the Planes may align so closely that the warp is almost not noticeable. Such regions are prone to certain unusual weather patterns or features such as the massive lake existing in the Eastern side of the Deadlands.

Sometimes creatures native to the Inner Planes traverse a warp into Shar. Mindless elementals traverse the regions surrounding the warp the came from, meandering slowly outward to continue to spread the influence of their native plane. However, these elementals rarely interact with settlements unless disturbed. More sapient folk such as genies might conversely seek out civilized society for entertainment. Their devious natures seldom end well for the natives, though, so more densely populated areas tend to learn to distrust these intruders.