  Water vapor geysers on Europa have been inferred from observations made by
the Galileo spacecraft, the Hubble Space Telescope, and the Keck Observatory.
Unlike the water-rich geysers observed on Enceladus, Europa's geysers appear to
be an intermittent phenomenon, and the dynamical mechanism permitting water to
sporadically erupt through a kilometers-thick ice sheet is not well understood.
Here we outline and explore the hypothesis that the Europan geysers are driven
by CO$_2$ gas released by dissociation and depressurization of CO$_2$ clathrate
hydrates initially sourced from the subsurface ocean. We show that CO$_2$
hydrates can become buoyant to the upper ice-water interface under plausible
oceanic conditions, namely, if the temperature or salinity conditions of a
density-stratified two-layer water column evolve to permit the onset of
convection that generates a single mixed layer. To quantitatively describe the
eruptions once the CO$_2$ has been released from the hydrate state, we extend a
one-dimensional hydrodynamical model that draws from the literature on volcanic
magma explosions on Earth. Our results indicate that for a sufficiently high
concentration of exsolved CO$_2$, these eruptions develop vertical velocities
of $\sim$700 m s$^{-1}$. These high velocities permit the ejecta to reach
heights of $\sim$200 km above the Europan surface, thereby explaining the
intermittent presence of water vapor at these high altitudes. Molecules ejected
via this process will persist in the Europan atmosphere for a duration of about
10 minutes, limiting the timescale over which geyser activity above the Europan
surface may be observable. Our proposed mechanism requires Europa's ice shell
thickness to be d$\lesssim$ 10 km.
