Final answer:
The invalid method to terminate an appurtenant easement among the given options is Revocation by the servient owner, as easements cannot typically be ended unilaterally by the servient tenement. Valid methods include expiration, release by the dominant tenement, and merger of the involved parcels.
Step-by-step explanation:
The termination of an appurtenant easement may occur in several ways, but not all of these options are valid. If we consider the options given, the correct answer is Revocation by the servient owner, as this is typically not a means of legally terminating an easement unless such a power has been explicitly granted in the easement agreement. Appurtenant easements are intended to benefit the dominant tenement, which is why they usually cannot be unilaterally terminated by the servient tenement owner.
A valid termination can take place through the expiration of the easement if it was created for a specific period. Another valid method is the release by the dominant tenement owner, whereby they can give up their rights granted by the easement. Last but not least, a merger of both the servient and dominant parcels, where ownership of both parcels becomes vested in one person, also effectively terminates the easement because an individual cannot have an easement on their own property.