  We discuss the role plasma injection plays in the formation of outflows in
Kerr spacetime. Using a model for the double flow established in the polar
region of a rotating black hole, we study the interplay between the different
processes that can power the outflow. In particular, we find two types of flows
with distinct properties that depend on the rate at which energy is deposited
in the magnetosphere. We discuss the implications of this result for gamma ray
bursts outflows.
