  It is known that there is a quantum mechanical tunneling process which,
through nucleation of a membrane, induces a transition between two de Sitter
spaces, lowering the cosmological constant. It is shown in this paper that a
different, new, membrane nucleation process exists, which, in addition to
lowering the cosmological constant, leaves a black hole behind. Once a black
hole is present, the relaxation of the cosmological constant may proceed via an
analog of the old process, which decreases the black hole horizon area, or via
the new process, which increases it.
