Magnensial Shift

The law of Magnensial shift happens whenever a magnetic force encounters a portal to another dimension. In such an event forces will create alternating fields of attraction and repulsion that will result in the creation of a porous landscape that will create smaller dimensional pockets within that will lead to the dimension from which caused this rift.
Also the attractive and repellant forces shall be eventually balanced by the alternate power.
 In the case of Arcadia colliding with the land mass of the originating continent. Given that Fae have existing ties to the elemental planes of existence portals shall be opened to these planes as well.
Dimensional travel and the creation of additional portals eats away at the consistency of the cohesion. Thus magical gateways, teleportation, are a force for erosion of the consistency of Jennara and threaten to unwind it.

Manifestation

One can see the law of magmensional shift happen whenever a magnet of very powerful force is laid in front of a portal. 
The walls of the portal will either spin inward or outward. Thus widening or decreasing the size of the portal. 
If one is careful this can have destructive consequences, particularly if a portal that is unwinding touches another portal and so forth perhaps creating a tumbling dominoes effect.

Localization

The strongest known application of this principle is of course the massive portal within the Tarinthean mountain beneath the city of Leathem.  Whereas Tarinthea mountain was once a very strong magnetic force the force of magnetism within it has been neutralized. Still the magnetism in the air present from so long ago does create problem for the many flying creatures that live and defend within that mountain.
The mountain of Tarinthea was caused from a recohesion of rocks spun off of Borea creating a solid house for the whirlpool of magic that led to the watery realms of Arcadia.

Type

Metaphysical, Arcane