Manifest Zones

Certain locations on, within, and above Eberron share a particularly close connection to one of the planes. These locations are known as manifest zones. For example, the Gloaming, a region within the Eldeen Reaches, has a close connection to Mabar, the plane of Endless Night. This connection enhances the power of negative energy in that region. The Shadow Marches have a number of small magic zones tied to Xoriat, the Realm of Madness, which both enhance transmutation magic and occasionally trigger wild magic effects (see page 149 of the Dungeon Master’s Guide). Parts of Aerenal have close ties to either Irian or Mabar, which accounts (at least in part) for the prominent role of necromantic magic and the Undying Court on the elven continent.
To an extent, manifest zones defy the normal interrelationship among the planes. The effects of a zone may wane slightly when its connected plane is remote and wax equally slightly when the plane draws closer, but the connection never vanishes entirely. Manifest zones sometimes allow passage between the planes when another plane becomes coterminous to the Material Plane.
Specific, important manifest zones are detailed in Chapter 7 of Eberron Campaign Setting. These zones are permanent and, in most cases, have had a profound impact on the land around them and the people who live there. Smaller and less important manifest zones are located across Eberron, and it is possible that new ones appear even as old ones wink out of existence. The appearance and disappearance of these zones does not seem to have any connection to the linked plane’s cosmological position relative to the Material Plane.
No manifest zone linked to Dal Quor exists. Minor zones and occasionally major zones linked to every other plane exist somewhere on Eberron.