  I propose a scenario according to which the dense compact circumstellar
matter (CSM) that the ejecta of many core collapse supernovae (CCSNe) collide
with within several days after explosion results from a dense zone where in
addition to the stellar wind there is gas that does not reach the escape
velocity. In this effervescent zone around red supergiant (RSG) stars, there
are dense clumps that are ejected from the vicinity of the RSG surface, rise to
radii of tens of astronomical units, and then fall back. I consider two simple
velocity distributions of the ejected clumps. I find that the density of the
bound mass can be tens of times that of the escaping wind, and therefore can
mimic a very high mass loss rate. The dense effervescent compact CSM zone can
(1) explain the collision of the ejecta of many CCSNe with a dense compact CSM
days after explosion, (2) facilitate very high mass loss rate if the star
experiences powerful pre-explosion activity, (3) form dust that obscures the
progenitor in the visible band, and (4) lead to an efficient mass transfer to a
stellar companion at separations of tens of astronomical units, if exists. The
effervescent zone might exist for thousands of years and more, and therefore
the effervescent CSM model removes the requirement from many type II CCSN
progenitors to experience a very strong outburst just years to months before
explosion.
