  Buoyant plumes, evolving free of boundary constraints, may develop
well-defined mushroom shaped heads. In normal plumes, overturning flow in the
head entrains less buoyant fluid from the surroundings as the head rises,
robbing the plume of its driving force. We consider here a new type of plume in
which the source of buoyancy is an autocatalytic chemical reaction. The
reaction occurs at a sharp front which separates reactants from less dense
products. In this type of plume, entrainment assists the reaction, producing
new buoyancy which fuels an accelerating plume head. When the head has grown to
a critical size, it detaches from the upwelling conduit, forming an
accelerating, buoyant vortex ring. This vortex is analogous to a rising smoke
ring. A second-generation head then develops at the point of
detachment.Multiple generations of chemical vortex rings can detach from a
single triggering event.
