  We report new observations of the H_2O megamaser in the Seyfert 2 galaxy
Mrk348. The line is redshifted by about 130 km s^-1 with respect to the
systemic velocity, is extremely broad, with a FWHM of 130 km s^-1, and has no
detectable high velocity components within 1500 km s^-1 on either side of the
observed line. The unusual line profile led us to suspect that this source,
might belong to a class of megamaser galaxies in which the amplified emission
is the result of an interaction between the radio jet and an encroaching
molecular cloud, rather than occurring in a circumnuclear disk. Our initial
VLBA observations show that the maser emission emanates entirely from a region
<0.25 pc in extent, located toward a continuum component thought to be
associated with the receding jet. The very high linewidth occurring on such
small spatial scales and the rapid variability indicate that the H_2O emission
is likely to arise from a shocked region at the interface between the energetic
jet material and the molecular gas in the cloud where the jet is boring
through. The orientation of the radio jets close to the plane of the sky also
results in shocks with the preferred orientation for strong masers from our
vantage point. Single-dish monitoring with the Effelsberg 100m telescope showed
that the line and continuum emission "flared" on very similar timescales. The
close temporal correlation between this activity in the maser emission and the
continuum flare further suggest that the masing region and the continuum
hotspots are nearly equidistant from the central engine and may be different
manifestations of the same dynamical events.
  (abridged abstract)
