  The Dominion Radio Astrophysical Observatory's Synthesis Telescope provides
the highest resolution data (1 arcmin and 0.82 km/s) to date of an HI worm
candidate. Observed as part of the Canadian Galactic Plane Survey,
mushroom-shaped GW 123.4-1.5 extends only a few hundred parsecs, contains ~10^5
solar masses of neutral hydrogen, and appears unrelated to a conventional shell
or chimney structure. Our preliminary Zeus-2d models use a single off-plane
explosion with a modest (~10^{51} ergs) energy input. These generic simulations
generate, interior to an expanding outer blast wave, a buoyant cloud whose
structure resembles the morphology of the observed feature. Unlike typical
model superbubbles, the stem can be narrow because its width is not governed by
the pressure behind the blast wave nor the disk scale height. Using this type
of approach it should be possible to more accurately model the thin stem and
other details of GW 123.4-1.5 in the future.
